# Zend_Db_Adapter

Zend_Db y sus clases relacionadas proporcionan una interfaz simple de base de datos SQL para Zend Framework. El Zend_Db_Adapter es la clase base que se utiliza para conectar su aplicación PHP A una base de datos ( RDBMS ). Existen diferentes clases Adapters(Adaptador) para cada tipo de base de datos ( RDBMS ).

Las clases Adapters de Zend_Db crean un puente entre las extensiones de base de datos de PHP hacia una interfaz común, para ayudarle a escribir aplicaciones PHP una sola vez y poder desplegar múltiples tipos de base de datos ( RDBMS ) con muy poco esfuerzo.

La Interfaz de la clase adaptador (adapter) es similar a la intefaz de la extensión PHP Data Objects . Zend_Db proporciona clases Adaptadoras para los drivers PDO de los siguientes tipos de RDBMS :

- IBM DB2 e Informix Dynamic Server (IDS), usando la extensión PHP pdo_ibm

- MySQL, usando la extensión PHP pdo_mysql

- Microsoft SQL Server, usando la extensión PHP pdo_mssql

- Oracle, usando la extensión PHP pdo_oci

- PostgreSQL, usando la extensión PHP pdo_pgsql

- SQLite, usando la extensión PHP pdo_sqlite

Ademas, Zend_Db proporciona clases Adaptadoras que utilizan las extensiones de base de datos de PHP de los siguientes tipos:

- MySQL, usando la extensión PHP mysqli

- Oracle, usando la extensión PHP oci8

- IBM DB2, usando la extensión PHP ibm_db2

- Firebird/Interbase, usando la extensión PHP php_interbase

Cada Zend_Db_Adaptador utiliza una extensión PHP . Se debe de tener habilitada la respectiva extensión en su entorno PHP para utilizar un Zend_Db_Adapter . Por ejemplo, si se utiliza una clase Zend_Db_Adapter basada en PDO , tiene que habilitar tanto la extensión PDO como el driver PDO del tipo de base de datos que se utiliza.

## Conexión a una Base de Datos utilizando un Adaptador

Esta sección describe cómo crear una instancia de un Adaptador de base de datos. Esto corresponde a establecer una conexión a un servidor de Base de Datos ( RDBMS ) desde su aplicación PHP .

### Usando un Constructor de Zend_Db Adapter

Se puede crear una instancia de un Adaptador utilizando su constructor. Un constructor de adaptador toma un argumento, que es un conjunto de parámetros utilizados para declarar la conexión.

Usando el Constructor de un Adaptador

    $db = new Zend_Db_Adapter_Pdo_Mysql(array(
        'host'     => '127.0.0.1',
        'username' => 'webuser',
        'password' => 'xxxxxxxx',
        'dbname'   => 'test'
    ));

### Usando el Zend_Db Factory

Como alternativa a la utilización directa del constructor de un adaptador, se puede crear una instancia del adaptador que use el método estático Zend_Db::factory() . Este método carga dinámicamente el archivo de clase Adaptador bajo demanda, usando Zend_Loader::loadClass() .

El primer argumento es una cadena que nombra al nombre base de la clase Adaptador. Por ejemplo, la cadena ' Pdo_Mysql ' corresponde a la clase Zend_Db_Adapter_Pdo_Mysql . El segundo argumento es el mismo array de parámetros que hubiera enviado al constructor del adaptador.

Usando el Adaptador del método factory

    // No necesitamos la siguiente declaración, porque
    // el archivo Zend_Db_Adapter_Pdo_Mysql será cargado para nosotros por el método
    // factory de Zend_Db.

    // require_once 'Zend/Db/Adapter/Pdo/Mysql.php';

    // carga automaticamente la clase Zend_Db_Adapter_Pdo_Mysql
    // y crea una instancia de la misma
    $db = Zend_Db::factory('Pdo_Mysql', array(
        'host'     => '127.0.0.1',
        'username' => 'webuser',
        'password' => 'xxxxxxxx',
        'dbname'   => 'test'
    ));

Si crea su propia clase que extiende a Zend_Db_Adapter_Abstract , pero no nombra su clase con el prefijo de paquete " Zend_Db_Adapter ", se puede utilizar el método factory() para cargar su adaptador si se especifica la parte principal de la clase del adaptador con la clave "adapterNamespace" en el conjunto de parámetros

Usando el método factory para una clase Adaptador personalizada

    // No tenemos que cargar el archivo de clase Adaptador
    // porque será cargado para nosotros por el método factory de Zend_Db.

    // Automáticamente carga la clase MyProject_Db_Adapter_Pdo_Mysql
    // y crea una instancia de ella.

    $db = Zend_Db::factory('Pdo_Mysql', array(
        'host'             => '127.0.0.1',
        'username'         => 'webuser',
        'password'         => 'xxxxxxxx',
        'dbname'           => 'test',
        'adapterNamespace' => 'MyProject_Db_Adapter'
    ));

### Uso de Zend_Config con Zend_Db Factory

Opcionalmente, se puede especificar cualquier argumento del método factory() como un objeto de tipo Zend_Config .

Si el primer argumento es un objeto de configuración, se espera que contenga una propiedad llamada adapter , conteniendo la cadena que da nombre al nombre base de la clase de adaptador. Opcionalmente, el objeto puede contener una propiedad llamada params , con subpropiedades correspondientes a nombres de parámetros del adaptador. Esto es usado sólo si el segundo argumento del método factory() se ha omitido.

Uso del método factory del Adaptador con un objeto Zend_Config

En el siguiente ejemplo, un objeto Zend_Config es creado usando un array. También puedes cargar los datos de un archivo externo, por ejemplo con Zend_Config_Ini o Zend_Config_Xml .

    $config = new Zend_Config(
        array(
            'database' => array(
                'adapter' => 'Mysqli',
                'params' => array(
                    'dbname' => 'test',
                    'username' => 'webuser',
                    'password' => 'secret',
                )
            )
        )
    );

    $db = Zend_Db::factory($config->database);

El segundo argumento del método factory() puede ser un array asociativo con entradas correspondientes a los parámetros del adaptador. Este argumento es opcional. Si el primer argumento es de tipo Zend_Config , se asume que tiene todos los parametros, y el segundo argumento es ignorado.

### Parámetros del Adaptador

El siguiente listado explica parámetros comunes reconocidos por Adaptador de clases Zend_Db .

- host : una string conteniendo un nombre de host o dirección IP del servidor de base de datos. Si la base de datos está corriendo sobre el mismo host que la aplicación PHP , usted puede utilizar 'localhost' o '127.0.0.1'.

- username : identificador de cuenta para autenticar una conexión al servidor RDBMS .

- password : la contraseña de la cuenta para la autenticación de credenciales de conexión con el servidor RDBMS

- dbname : nombre de la base de datos en el servidor RDBMS .

- port : algunos servidores RDBMS pueden aceptar conexiones de red sobre un número de puerto específico. El parámetro del puerto le permite especificar el puerto al que su aplicación PHP se conecta, para que concuerde el puerto configurado en el servidor RDBMS .

- charset : specify the charset used for the connection.

- options : : este parámetro es un array asociativo de opciones que son genéricas a todas las clases Zend_Db_Adapter .

- driver_options : este parámetro es un array asociativo de opciones adicionales para una extensión de base de datos dada. un uso típico de este parámetro es establecer atributos de un driver PDO .

- adapterNamespace : nombre de la parte inicial del nombre de las clase para el adaptador, en lugar de ' Zend_Db_Adapter '. Utilice esto si usted necesita usar el método factory() para cargar un adaptador de clase de base de datos que no sea de Zend.

Passing the case-folding option to the factory

Usted puede pasar esta opción específica por la constante `Zend_Db::CASE_FOLDING` . Este corresponde al atributo `ATTR_CASE` en los drivers de base de datos PDO e IBM DB2, ajustando la sensibilidad de las claves tipo cadena en los resultados de consultas. La opción toma los valores `Zend_Db::CASE_NATURAL` (el predeterminado), `Zend_Db::CASE_UPPER` , y `Zend_Db::CASE_LOWER` .

    $options = array(
        Zend_Db::CASE_FOLDING => Zend_Db::CASE_UPPER
    );

    $params = array(
        'host'           => '127.0.0.1',
        'username'       => 'webuser',
        'password'       => 'xxxxxxxx',
        'dbname'         => 'test',
        'options'        => $options
    );

    $db = Zend_Db::factory('Db2', $params);

Passing the auto-quoting option to the factory

Usted puede especificar esta opción por la constante `Zend_Db::AUTO_QUOTE_IDENTIFIERS` . Si el valor es `TRUE` (el predeterminado), los identificadores como nombres de tabla, nombres de columna, e incluso los alias son delimitados en la sintaxis SQL generada por el Adatador del objeto. Esto hace que sea sencillo utilizar identificadores que contengan palabras reservadas de SQL , o caracteres especiales. Si el valor es `FALSE` , los identificadores no son delimitados automáticamente. Si usted necesita delimitar identificadores, debe hacer usted mismo utilizando el método quoteIdentifier() .

    $options = array(
        Zend_Db::AUTO_QUOTE_IDENTIFIERS => false
    );

    $params = array(
        'host'           => '127.0.0.1',
        'username'       => 'webuser',
        'password'       => 'xxxxxxxx',
        'dbname'         => 'test',
        'options'        => $options
    );

    $db = Zend_Db::factory('Pdo_Mysql', $params);

Passing PDO driver options to the factory

    $pdoParams = array(
        PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => true
    );

    $params = array(
        'host'           => '127.0.0.1',
        'username'       => 'webuser',
        'password'       => 'xxxxxxxx',
        'dbname'         => 'test',
        'driver_options' => $pdoParams
    );

    $db = Zend_Db::factory('Pdo_Mysql', $params);

    echo $db->getConnection()
            ->getAttribute(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY);

Passing Serialization Options to the Factory

    $options = array(
        Zend_Db::ALLOW_SERIALIZATION => false
    );

    $params = array(
        'host'           => '127.0.0.1',
        'username'       => 'webuser',
        'password'       => 'xxxxxxxx',
        'dbname'         => 'test',
        'options'        => $options
    );

    $db = Zend_Db::factory('Pdo_Mysql', $params);

### Managing Lazy Connections

Creating an instance of an Adapter class does not immediately connect to the RDBMS server. The Adapter saves the connection parameters, and makes the actual connection on demand, the first time you need to execute a query. This ensures that creating an Adapter object is quick and inexpensive. You can create an instance of an Adapter even if you are not certain that you need to run any database queries during the current request your application is serving.

If you need to force the Adapter to connect to the RDBMS , use the getConnection() method. This method returns an object for the connection as represented by the respective PHP database extension. For example, if you use any of the Adapter classes for PDO drivers, then getConnection() returns the PDO object, after initiating it as a live connection to the specific database.

It can be useful to force the connection if you want to catch any exceptions it throws as a result of invalid account credentials, or other failure to connect to the RDBMS server. These exceptions are not thrown until the connection is made, so it can help simplify your application code if you handle the exceptions in one place, instead of at the time of the first query against the database.

Additionally, an adapter can get serialized to store it, for example, in a session variable. This can be very useful not only for the adapter itself, but for other objects that aggregate it, like a Zend_Db_Select object. By default, adapters are allowed to be serialized, if you don't want it, you should consider passing the `Zend_Db::ALLOW_SERIALIZATION` option with `FALSE` , see the example above. To respect lazy connections principle, the adapter won't reconnect itself after being unserialized. You must then call getConnection() yourself. You can make the adapter auto-reconnect by passing the `Zend_Db::AUTO_RECONNECT_ON_UNSERIALIZE` with `TRUE` as an adapter option.

Handling connection exceptions

    try {
        $db = Zend_Db::factory('Pdo_Mysql', $parameters);
        $db->getConnection();
    } catch (Zend_Db_Adapter_Exception $e) {
        // perhaps a failed login credential, or perhaps the RDBMS is not running
    } catch (Zend_Exception $e) {
        // perhaps factory() failed to load the specified Adapter class
    }

## La base de datos de ejemplo

En la documentación de las clases Zend_Db , usamos un conjunto sencillo de tablas para ilustrar el uso de las clases y métodos. Estas tablas de ejemplo permiten almacenar información para localizar bugs en un proyecto de desarrollo de software. La base de datos contiene cuatro tablas:

- accounts almacena información sobre cada usuario que hace el seguimiento de bugs.

- products almacena información sobre cada producto para el que pueden registrarse bugs.

- bugs almacena información sobre bugs, incluyendo el estado actual del bug, la persona que informó sobre el bug, la persona que está asignada para corregir el bug, y la persona que está asignada para verificar la corrección.

- bugs_products stores a relationship between bugs and products. This implements a many-to-many relationship, because a given bug may be relevant to multiple products, and of course a given product can have multiple bugs.

La siguiente definición de datos SQL en lenguaje pseudocódigo describe las tablas de esta base de datos de ejemplo. Estas tablas de ejemplo son usadas ampliamente por los tests unitarios automatizados de Zend_Db .

    CREATE TABLE accounts (
      account_name      VARCHAR(100) NOT NULL PRIMARY KEY
    );

    CREATE TABLE products (
      product_id        INTEGER NOT NULL PRIMARY KEY,
      product_name      VARCHAR(100)
    );

    CREATE TABLE bugs (
      bug_id            INTEGER NOT NULL PRIMARY KEY,
      bug_description   VARCHAR(100),
      bug_status        VARCHAR(20),
      reported_by       VARCHAR(100) REFERENCES accounts(account_name),
      assigned_to       VARCHAR(100) REFERENCES accounts(account_name),
      verified_by       VARCHAR(100) REFERENCES accounts(account_name)
    );

    CREATE TABLE bugs_products (
      bug_id            INTEGER NOT NULL REFERENCES bugs,
      product_id        INTEGER NOT NULL REFERENCES products,
      PRIMARY KEY       (bug_id, product_id)
    );

Also notice that the `bugs` table contains multiple foreign key references to the `accounts` table. Each of these foreign keys may reference a different row in the `accounts` table for a given bug.

The diagram below illustrates the physical data model of the example database.

## Reading Query Results

This section describes methods of the Adapter class with which you can run SELECT queries and retrieve the query results.

### Fetching a Complete Result Set

You can run a SQL SELECT query and retrieve its results in one step using the fetchAll() method.

The first argument to this method is a string containing a SELECT statement. Alternatively, the first argument can be an object of class Zend_Db_Select . The Adapter automatically converts this object to a string representation of the SELECT statement.

The second argument to fetchAll() is an array of values to substitute for parameter placeholders in the SQL statement.

Using fetchAll()

    $sql = 'SELECT * FROM bugs WHERE bug_id = ?';

    $result = $db->fetchAll($sql, 2);

### Changing the Fetch Mode

By default, fetchAll() returns an array of rows, each of which is an associative array. The keys of the associative array are the columns or column aliases named in the select query.

You can specify a different style of fetching results using the setFetchMode() method. The modes supported are identified by constants:

- `Zend_Db::FETCH_ASSOC` : return data in an array of associative arrays. The array keys are column names, as strings. This is the default fetch mode for Zend_Db_Adapter classes.

  Note that if your select-list contains more than one column with the same name, for example if they are from two different tables in a JOIN, there can be only one entry in the associative array for a given name. If you use the FETCH_ASSOC mode, you should specify column aliases in your SELECT query to ensure that the names result in unique array keys.

  By default, these strings are returned as they are returned by the database driver. This is typically the spelling of the column in the RDBMS server. You can specify the case for these strings, using the `Zend_Db::CASE_FOLDING` option. Specify this when instantiating the Adapter. See .

- `Zend_Db::FETCH_NUM` : return data in an array of arrays. The arrays are indexed by integers, corresponding to the position of the respective field in the select-list of the query.

- `Zend_Db::FETCH_BOTH` : return data in an array of arrays. The array keys are both strings as used in the FETCH_ASSOC mode, and integers as used in the FETCH_NUM mode. Note that the number of elements in the array is double that which would be in the array if you used either FETCH_ASSOC or FETCH_NUM.

- `Zend_Db::FETCH_COLUMN` : return data in an array of values. The value in each array is the value returned by one column of the result set. By default, this is the first column, indexed by 0.

- `Zend_Db::FETCH_OBJ` : return data in an array of objects. The default class is the PHP built-in class stdClass. Columns of the result set are available as public properties of the object.

Using setFetchMode()

    $db->setFetchMode(Zend_Db::FETCH_OBJ);

    $result = $db->fetchAll('SELECT * FROM bugs WHERE bug_id = ?', 2);

    // $result is an array of objects
    echo $result[0]->bug_description;

### Fetching a Result Set as an Associative Array

The fetchAssoc() method returns data in an array of associative arrays, regardless of what value you have set for the fetch mode.

Using fetchAssoc()

    $db->setFetchMode(Zend_Db::FETCH_OBJ);

    $result = $db->fetchAssoc('SELECT * FROM bugs WHERE bug_id = ?', 2);

    // $result is an array of associative arrays, in spite of the fetch mode
    echo $result[0]['bug_description'];

### Fetching a Single Column from a Result Set

The fetchCol() method returns data in an array of values, regardless of the value you have set for the fetch mode. This only returns the first column returned by the query. Any other columns returned by the query are discarded. If you need to return a column other than the first, see .

Using fetchCol()

    $db->setFetchMode(Zend_Db::FETCH_OBJ);

    $result = $db->fetchCol(
        'SELECT bug_description, bug_id FROM bugs WHERE bug_id = ?', 2);

    // contains bug_description; bug_id is not returned
    echo $result[0];

### Fetching Key-Value Pairs from a Result Set

The fetchPairs() method returns data in an array of key-value pairs, as an associative array with a single entry per row. The key of this associative array is taken from the first column returned by the SELECT query. The value is taken from the second column returned by the SELECT query. Any other columns returned by the query are discarded.

You should design the SELECT query so that the first column returned has unique values. If there are duplicates values in the first column, entries in the associative array will be overwritten.

Using fetchPairs()

    $db->setFetchMode(Zend_Db::FETCH_OBJ);

    $result = $db->fetchPairs('SELECT bug_id, bug_status FROM bugs');

    echo $result[2];

### Fetching a Single Row from a Result Set

The fetchRow() method returns data using the current fetch mode, but it returns only the first row fetched from the result set.

Using fetchRow()

    $db->setFetchMode(Zend_Db::FETCH_OBJ);

    $result = $db->fetchRow('SELECT * FROM bugs WHERE bug_id = 2');

    // note that $result is a single object, not an array of objects
    echo $result->bug_description;

### Fetching a Single Scalar from a Result Set

The fetchOne() method is like a combination of fetchRow() with fetchCol() , in that it returns data only for the first row fetched from the result set, and it returns only the value of the first column in that row. Therefore it returns only a single scalar value, not an array or an object.

Using fetchOne()

    $result = $db->fetchOne('SELECT bug_status FROM bugs WHERE bug_id = 2');

    // this is a single string value
    echo $result;

## Writing Changes to the Database

You can use the Adapter class to write new data or change existing data in your database. This section describes methods to do these operations.

### Inserting Data

You can add new rows to a table in your database using the insert() method. The first argument is a string that names the table, and the second argument is an associative array, mapping column names to data values.

Inserting in a Table

    $data = array(
        'created_on'      => '2007-03-22',
        'bug_description' => 'Something wrong',
        'bug_status'      => 'NEW'
    );

    $db->insert('bugs', $data);

Columns you exclude from the array of data are not specified to the database. Therefore, they follow the same rules that an SQL INSERT statement follows: if the column has a DEFAULT clause, the column takes that value in the row created, otherwise the column is left in a NULL state.

By default, the values in your data array are inserted using parameters. This reduces risk of some types of security issues. You don't need to apply escaping or quoting to values in the data array.

You might need values in the data array to be treated as SQL expressions, in which case they should not be quoted. By default, all data values passed as strings are treated as string literals. To specify that the value is an SQL expression and therefore should not be quoted, pass the value in the data array as an object of type Zend_Db_Expr instead of a plain string.

Inserting Expressions in a Table

    $data = array(
        'created_on'      => new Zend_Db_Expr('CURDATE()'),
        'bug_description' => 'Something wrong',
        'bug_status'      => 'NEW'
    );

    $db->insert('bugs', $data);

### Retrieving a Generated Value

Some RDBMS brands support auto-incrementing primary keys. A table defined this way generates a primary key value automatically during an INSERT of a new row. The return value of the insert() method is not the last inserted ID, because the table might not have an auto-incremented column. Instead, the return value is the number of rows affected (usually 1).

If your table is defined with an auto-incrementing primary key, you can call the lastInsertId() method after the insert. This method returns the last value generated in the scope of the current database connection.

Using lastInsertId() for an Auto-Increment Key

    $db->insert('bugs', $data);

    // return the last value generated by an auto-increment column
    $id = $db->lastInsertId();

Some RDBMS brands support a sequence object, which generates unique values to serve as primary key values. To support sequences, the lastInsertId() method accepts two optional string arguments. These arguments name the table and the column, assuming you have followed the convention that a sequence is named using the table and column names for which the sequence generates values, and a suffix "_seq". This is based on the convention used by PostgreSQL when naming sequences for SERIAL columns. For example, a table "bugs" with primary key column "bug_id" would use a sequence named "bugs_bug_id_seq".

Using lastInsertId() for a Sequence

    $db->insert('bugs', $data);

    // return the last value generated by sequence 'bugs_bug_id_seq'.
    $id = $db->lastInsertId('bugs', 'bug_id');

    // alternatively, return the last value generated by sequence 'bugs_seq'.
    $id = $db->lastInsertId('bugs');

If the name of your sequence object does not follow this naming convention, use the lastSequenceId() method instead. This method takes a single string argument, naming the sequence literally.

Using lastSequenceId()

    $db->insert('bugs', $data);

    // return the last value generated by sequence 'bugs_id_gen'.
    $id = $db->lastSequenceId('bugs_id_gen');

For RDBMS brands that don't support sequences, including MySQL, Microsoft SQL Server, and SQLite, the arguments to the lastInsertId() method are ignored, and the value returned is the most recent value generated for any table by INSERT operations during the current connection. For these RDBMS brands, the lastSequenceId() method always returns `NULL` .

Why Not Use "SELECT MAX(id) FROM table"?

Sometimes this query returns the most recent primary key value inserted into the table. However, this technique is not safe to use in an environment where multiple clients are inserting records to the database. It is possible, and therefore is bound to happen eventually, that another client inserts another row in the instant between the insert performed by your client application and your query for the MAX(id) value. Thus the value returned does not identify the row you inserted, it identifies the row inserted by some other client. There is no way to know when this has happened.

Using a strong transaction isolation mode such as "repeatable read" can mitigate this risk, but some RDBMS brands don't support the transaction isolation required for this, or else your application may use a lower transaction isolation mode by design.

Furthermore, using an expression like "MAX(id)+1" to generate a new value for a primary key is not safe, because two clients could do this query simultaneously, and then both use the same calculated value for their next INSERT operation.

All RDBMS brands provide mechanisms to generate unique values, and to return the last value generated. These mechanisms necessarily work outside of the scope of transaction isolation, so there is no chance of two clients generating the same value, and there is no chance that the value generated by another client could be reported to your client's connection as the last value generated.

### Updating Data

You can update rows in a database table using the update() method of an Adapter. This method takes three arguments: the first is the name of the table; the second is an associative array mapping columns to change to new values to assign to these columns.

The values in the data array are treated as string literals. See for information on using SQL expressions in the data array.

The third argument is a string containing an SQL expression that is used as criteria for the rows to change. The values and identifiers in this argument are not quoted or escaped. You are responsible for ensuring that any dynamic content is interpolated into this string safely. See for methods to help you do this.

The return value is the number of rows affected by the update operation.

Updating Rows

    $data = array(
        'updated_on'      => '2007-03-23',
        'bug_status'      => 'FIXED'
    );

    $n = $db->update('bugs', $data, 'bug_id = 2');

If you omit the third argument, then all rows in the database table are updated with the values specified in the data array.

If you provide an array of strings as the third argument, these strings are joined together as terms in an expression separated by `AND` operators.

Updating Rows Using an Array of Expressions

    $data = array(
        'updated_on'      => '2007-03-23',
        'bug_status'      => 'FIXED'
    );

    $where[] = "reported_by = 'goofy'";
    $where[] = "bug_status = 'OPEN'";

    $n = $db->update('bugs', $data, $where);

    // Resulting SQL is:
    //  UPDATE "bugs" SET "update_on" = '2007-03-23', "bug_status" = 'FIXED'
    //  WHERE ("reported_by" = 'goofy') AND ("bug_status" = 'OPEN')

### Deleting Data

You can delete rows from a database table using the delete() method. This method takes two arguments: the first is a string naming the table.

The second argument is a string containing an SQL expression that is used as criteria for the rows to delete. The values and identifiers in this argument are not quoted or escaped. You are responsible for ensuring that any dynamic content is interpolated into this string safely. See for methods to help you do this.

The return value is the number of rows affected by the delete operation.

Deleting Rows

    $n = $db->delete('bugs', 'bug_id = 3');

If you omit the second argument, the result is that all rows in the database table are deleted.

If you provide an array of strings as the second argument, these strings are joined together as terms in an expression separated by `AND` operators.

## Quoting Values and Identifiers

When you form SQL queries, often it is the case that you need to include the values of PHP variables in SQL expressions. This is risky, because if the value in a PHP string contains certain symbols, such as the quote symbol, it could result in invalid SQL . For example, notice the imbalanced quote characters in the following query:

    $name = "O'Reilly";
    $sql = "SELECT * FROM bugs WHERE reported_by = '$name'";

    echo $sql;
    // SELECT * FROM bugs WHERE reported_by = 'O'Reilly'

Even worse is the risk that such code mistakes might be exploited deliberately by a person who is trying to manipulate the function of your web application. If they can specify the value of a PHP variable through the use of an HTTP parameter or other mechanism, they might be able to make your SQL queries do things that you didn't intend them to do, such as return data to which the person should not have privilege to read. This is a serious and widespread technique for violating application security, known as "SQL Injection" (see http://en.wikipedia.org/wiki/SQL_Injection ).

The Zend_Db Adapter class provides convenient functions to help you reduce vulnerabilities to SQL Injection attacks in your PHP code. The solution is to escape special characters such as quotes in PHP values before they are interpolated into your SQL strings. This protects against both accidental and deliberate manipulation of SQL strings by PHP variables that contain special characters.

### Using quote()

The quote() method accepts a single argument, a scalar string value. It returns the value with special characters escaped in a manner appropriate for the RDBMS you are using, and surrounded by string value delimiters. The standard SQL string value delimiter is the single-quote ( `'` ).

Using quote()

    $name = $db->quote("O'Reilly");
    echo $name;
    // 'O\'Reilly'

    $sql = "SELECT * FROM bugs WHERE reported_by = $name";

    echo $sql;
    // SELECT * FROM bugs WHERE reported_by = 'O\'Reilly'

Note that the return value of quote() includes the quote delimiters around the string. This is different from some functions that escape special characters but do not add the quote delimiters, for example mysql_real_escape_string() .

Values may need to be quoted or not quoted according to the SQL datatype context in which they are used. For instance, in some RDBMS brands, an integer value must not be quoted as a string if it is compared to an integer-type column or expression. In other words, the following is an error in some SQL implementations, assuming `intColumn` has a SQL datatype of `INTEGER`

    SELECT * FROM atable WHERE intColumn = '123'

You can use the optional second argument to the quote() method to apply quoting selectively for the SQL datatype you specify.

Using quote() with a SQL Type

    $value = '1234';
    $sql = 'SELECT * FROM atable WHERE intColumn = '
         . $db->quote($value, 'INTEGER');

Each Zend_Db_Adapter class has encoded the names of numeric SQL datatypes for the respective brand of RDBMS . You can also use the constants `Zend_Db::INT_TYPE` , `Zend_Db::BIGINT_TYPE` , and `Zend_Db::FLOAT_TYPE` to write code in a more RDBMS -independent way.

Zend_Db_Table specifies SQL types to quote() automatically when generating SQL queries that reference a table's key columns.

### Using quoteInto()

The most typical usage of quoting is to interpolate a PHP variable into a SQL expression or statement. You can use the quoteInto() method to do this in one step. This method takes two arguments: the first argument is a string containing a placeholder symbol ( `?` ), and the second argument is a value or PHP variable that should be substituted for that placeholder.

The placeholder symbol is the same symbol used by many RDBMS brands for positional parameters, but the quoteInto() method only emulates query parameters. The method simply interpolates the value into the string, escapes special characters, and applies quotes around it. True query parameters maintain the separation between the SQL string and the parameters as the statement is parsed in the RDBMS server.

Using quoteInto()

    $sql = $db->quoteInto("SELECT * FROM bugs WHERE reported_by = ?", "O'Reilly");

    echo $sql;
    // SELECT * FROM bugs WHERE reported_by = 'O\'Reilly'

You can use the optional third parameter of quoteInto() to specify the SQL datatype. Numeric datatypes are not quoted, and other types are quoted.

Using quoteInto() with a SQL Type

    $sql = $db
        ->quoteInto("SELECT * FROM bugs WHERE bug_id = ?", '1234', 'INTEGER');

    echo $sql;
    // SELECT * FROM bugs WHERE reported_by = 1234

### Using quoteIdentifier()

Values are not the only part of SQL syntax that might need to be variable. If you use PHP variables to name tables, columns, or other identifiers in your SQL statements, you might need to quote these strings too. By default, SQL identifiers have syntax rules like PHP and most other programming languages. For example, identifiers should not contain spaces, certain punctuation or special characters, or international characters. Also certain words are reserved for SQL syntax, and should not be used as identifiers.

However, SQL has a feature called delimited identifiers , which allows broader choices for the spelling of identifiers. If you enclose a SQL identifier in the proper types of quotes, you can use identifiers with spellings that would be invalid without the quotes. Delimited identifiers can contain spaces, punctuation, or international characters. You can also use SQL reserved words if you enclose them in identifier delimiters.

The quoteIdentifier() method works like quote() , but it applies the identifier delimiter characters to the string according to the type of Adapter you use. For example, standard SQL uses double-quotes ( `"` ) for identifier delimiters, and most RDBMS brands use that symbol. MySQL uses back-quotes ( ``` ) by default. The quoteIdentifier() method also escapes special characters within the string argument.

Using quoteIdentifier()

    // we might have a table name that is an SQL reserved word
    $tableName = $db->quoteIdentifier("order");

    $sql = "SELECT * FROM $tableName";

    echo $sql
    // SELECT * FROM "order"

SQL delimited identifiers are case-sensitive, unlike unquoted identifiers. Therefore, if you use delimited identifiers, you must use the spelling of the identifier exactly as it is stored in your schema, including the case of the letters.

In most cases where SQL is generated within Zend_Db classes, the default is that all identifiers are delimited automatically. You can change this behavior with the option `Zend_Db::AUTO_QUOTE_IDENTIFIERS` . Specify this when instantiating the Adapter. See .

## Controlling Database Transactions

Databases define transactions as logical units of work that can be committed or rolled back as a single change, even if they operate on multiple tables. All queries to a database are executed within the context of a transaction, even if the database driver manages them implicitly. This is called auto-commit mode, in which the database driver creates a transaction for every statement you execute, and commits that transaction after your SQL statement has been executed. By default, all Zend_Db Adapter classes operate in auto-commit mode.

Alternatively, you can specify the beginning and resolution of a transaction, and thus control how many SQL queries are included in a single group that is committed (or rolled back) as a single operation. Use the beginTransaction() method to initiate a transaction. Subsequent SQL statements are executed in the context of the same transaction until you resolve it explicitly.

To resolve the transaction, use either the commit() or rollBack() methods. The commit() method marks changes made during your transaction as committed, which means the effects of these changes are shown in queries run in other transactions.

The rollBack() method does the opposite: it discards the changes made during your transaction. The changes are effectively undone, and the state of the data returns to how it was before you began your transaction. However, rolling back your transaction has no effect on changes made by other transactions running concurrently.

After you resolve this transaction, Zend_Db_Adapter returns to auto-commit mode until you call beginTransaction() again.

Managing a Transaction to Ensure Consistency

    // Start a transaction explicitly.
    $db->beginTransaction();

    try {
        // Attempt to execute one or more queries:
        $db->query(...);
        $db->query(...);
        $db->query(...);

        // If all succeed, commit the transaction and all changes
        // are committed at once.
        $db->commit();

    } catch (Exception $e) {
        // If any of the queries failed and threw an exception,
        // we want to roll back the whole transaction, reversing
        // changes made in the transaction, even those that succeeded.
        // Thus all changes are committed together, or none are.
        $db->rollBack();
        echo $e->getMessage();
    }

## Listing and Describing Tables

The listTables() method returns an array of strings, naming all tables in the current database.

The describeTable() method returns an associative array of metadata about a table. Specify the name of the table as a string in the first argument to this method. The second argument is optional, and names the schema in which the table exists.

The keys of the associative array returned are the column names of the table. The value corresponding to each column is also an associative array, with the following keys and values:

Metadata Fields Returned by describeTable()

Key | Type | Description
--- | --- | ---
`SCHEMA_NAME` | (string) | Name of the database schema in which this table exists.
`TABLE_NAME` | (string) | Name of the table to which this column belongs.
`COLUMN_NAME` | (string) | Name of the column.
`COLUMN_POSITION` | (integer) | Ordinal position of the column in the table.
`DATA_TYPE` | (string) | RDBMS name of the datatype of the column.
`DEFAULT` | (string) | Default value for the column, if any.
`NULLABLE` | (boolean) | `TRUE` if the column accepts SQL `NULL`s, `FALSE` if the column has a `NOT` `NULL` constraint.
`LENGTH` | (integer) | Length or size of the column as reported by the RDBMS .
`SCALE` | (integer) | Scale of SQL NUMERIC or `DECIMAL` type.
`PRECISION` | (integer) | Precision of SQL NUMERIC or `DECIMAL` type.
`UNSIGNED` | (boolean) | `TRUE` if an integer-based type is reported as `UNSIGNED` .
`PRIMARY` | (boolean) | `TRUE` if the column is part of the primary key of this table.
`PRIMARY_POSITION` | (integer) | Ordinal position (1-based) of the column in the primary key.
`IDENTITY` | (boolean) | `TRUE` if the column uses an auto-generated value.

How the IDENTITY Metadata Field Relates to Specific RDBMSs

The IDENTITY metadata field was chosen as an 'idiomatic' term to represent a relation to surrogate keys. This field can be commonly known by the following values:-

- `IDENTITY` - DB2, MSSQL

- `AUTO_INCREMENT` - MySQL

- `SERIAL` - PostgreSQL

- `SEQUENCE` - Oracle

If no table exists matching the table name and optional schema name specified, then describeTable() returns an empty array.

## Closing a Connection

Normally it is not necessary to close a database connection. PHP automatically cleans up all resources and the end of a request. Database extensions are designed to close the connection as the reference to the resource object is cleaned up.

However, if you have a long-duration PHP script that initiates many database connections, you might need to close the connection, to avoid exhausting the capacity of your RDBMS server. You can use the Adapter's closeConnection() method to explicitly close the underlying database connection.

Since release 1.7.2, you could check you are currently connected to the RDBMS server with the method isConnected() . This means that a connection resource has been initiated and wasn't closed. This function is not currently able to test for example a server side closing of the connection. This is internally use to close the connection. It allow you to close the connection multiple times without errors. It was already the case before 1.7.2 for PDO adapters but not for the others.

Closing a Database Connection

    $db->closeConnection();

Does Zend_Db Support Persistent Connections?

Yes, persistence is supported through the addition of the persistent flag set to true in the configuration (not driver_configuration) of an adapter in Zend_Db .

Using the Persitence Flag with the Oracle Adapter

    $db = Zend_Db::factory('Oracle', array(
        'host'       => '127.0.0.1',
        'username'   => 'webuser',
        'password'   => 'xxxxxxxx',
        'dbname'     => 'test',
        'persistent' => true
    ));

Please note that using persistent connections can cause an excess of idle connections on the RDBMS server, which causes more problems than any performance gain you might achieve by reducing the overhead of making connections.

Database connections have state. That is, some objects in the RDBMS server exist in session scope. Examples are locks, user variables, temporary tables, and information about the most recently executed query, such as rows affected, and last generated id value. If you use persistent connections, your application could access invalid or privileged data that were created in a previous PHP request.

Currently, only Oracle, DB2, and the PDO adapters (where specified by PHP ) support persistence in Zend_Db .

## Running Other Database Statements

There might be cases in which you need to access the connection object directly, as provided by the PHP database extension. Some of these extensions may offer features that are not surfaced by methods of Zend_Db_Adapter_Abstract .

For example, all SQL statements run by Zend_Db are prepared, then executed. However, some database features are incompatible with prepared statements. DDL statements like CREATE and ALTER cannot be prepared in MySQL. Also, SQL statements don't benefit from the MySQL Query Cache , prior to MySQL 5.1.17.

Most PHP database extensions provide a method to execute SQL statements without preparing them. For example, in PDO , this method is exec() . You can access the connection object in the PHP extension directly using getConnection().

Running a Non-Prepared Statement in a PDO Adapter

    $result = $db->getConnection()->exec('DROP TABLE bugs');

Similarly, you can access other methods or properties that are specific to PHP database extensions. Be aware, though, that by doing this you might constrain your application to the interface provided by the extension for a specific brand of RDBMS .

In future versions of Zend_Db , there will be opportunities to add method entry points for functionality that is common to the supported PHP database extensions. This will not affect backward compatibility.

## Retrieving Server Version

Since release 1.7.2, you could retrieve the server version in PHP syntax style to be able to use version_compare() . If the information isn't available, you will receive `NULL` .

Verifying server version before running a query

    $version = $db->getServerVersion();
    if (!is_null($version)) {
        if (version_compare($version, '5.0.0', '>=')) {
            // do something
        } else {
            // do something else
        }
    } else {
        // impossible to read server version
    }

## Notes on Specific Adapters

This section lists differences between the Adapter classes of which you should be aware.

### IBM DB2

- Specify this Adapter to the factory() method with the name 'Db2'.

- This Adapter uses the PHP extension ibm_db2.

- IBM DB2 supports both sequences and auto-incrementing keys. Therefore the arguments to lastInsertId() are optional. If you give no arguments, the Adapter returns the last value generated for an auto-increment key. If you give arguments, the Adapter returns the last value generated by the sequence named according to the convention ' table _ column _seq'.

### MySQLi

- Specify this Adapter to the factory() method with the name 'Mysqli'.

- This Adapter utilizes the PHP extension mysqli.

- MySQL does not support sequences, so lastInsertId() ignores its arguments and always returns the last value generated for an auto-increment key. The lastSequenceId() method returns `NULL` .

### Oracle

- Specify this Adapter to the factory() method with the name 'Oracle'.

- This Adapter uses the PHP extension oci8.

- Oracle does not support auto-incrementing keys, so you should specify the name of a sequence to lastInsertId() or lastSequenceId() .

- The Oracle extension does not support positional parameters. You must use named parameters.

- Currently the `Zend_Db::CASE_FOLDING` option is not supported by the Oracle adapter. To use this option with Oracle, you must use the PDO OCI adapter.

- By default, LOB fields are returned as OCI-Lob objects. You could retrieve them as string for all requests by using driver options `'lob_as_string'` or for particular request by using setLobAsString(boolean) on adapter or on statement.

### Microsoft SQL Server

- Specify this Adapter to the factory() method with the name 'Sqlsrv'.

- This Adapter uses the PHP extension sqlsrv

- Microsoft SQL Server does not support sequences, so lastInsertId() ignores primary key argument and returns the last value generated for an auto-increment key if a table name is specified or a last insert query returned id. The lastSequenceId() method returns `NULL` .

- Zend_Db_Adapter_Sqlsrv sets `QUOTED_IDENTIFIER ON` immediately after connecting to a SQL Server database. This makes the driver use the standard SQL identifier delimiter symbol ( " ) instead of the proprietary square-brackets syntax SQL Server uses for delimiting identifiers.

- You can specify driver_options as a key in the options array. The value can be a anything from here http://msdn.microsoft.com/en-us/library/cc296161(SQL.90).aspx .

- You can use setTransactionIsolationLevel() to set isolation level for current connection. The value can be `SQLSRV_TXN_READ_UNCOMMITTED` , `SQLSRV_TXN_READ_COMMITTED` , `SQLSRV_TXN_REPEATABLE_READ` , `SQLSRV_TXN_SNAPSHOT` or `SQLSRV_TXN_SERIALIZABLE` .

- As of Zend Framework 1.9, the minimal supported build of the PHP SQL Server extension from Microsoft is 1.0.1924.0. and the MSSQL Server Native Client version 9.00.3042.00.

### PDO for IBM DB2 and Informix Dynamic Server (IDS)

- Specify this Adapter to the factory() method with the name 'Pdo_Ibm'.

- This Adapter uses the PHP extensions pdo and pdo_ibm.

- You must use at least PDO _IBM extension version 1.2.2. If you have an earlier version of this extension, you must upgrade the PDO _IBM extension from PECL .

### PDO Microsoft SQL Server

- Specify this Adapter to the factory() method with the name 'Pdo_Mssql'.

- This Adapter uses the PHP extensions pdo and pdo_mssql.

- Microsoft SQL Server does not support sequences, so lastInsertId() ignores its arguments and always returns the last value generated for an auto-increment key. The lastSequenceId() method returns `NULL` .

- If you are working with unicode strings in an encoding other than UCS-2 (such as UTF-8), you may have to perform a conversion in your application code or store the data in a binary column. Please refer to Microsoft's Knowledge Base for more information.

- Zend_Db_Adapter_Pdo_Mssql sets `QUOTED_IDENTIFIER ON` immediately after connecting to a SQL Server database. This makes the driver use the standard SQL identifier delimiter symbol ( `"` ) instead of the proprietary square-brackets syntax SQL Server uses for delimiting identifiers.

- You can specify `pdoType` as a key in the options array. The value can be "mssql" (the default), "dblib", "freetds", or "sybase". This option affects the DSN prefix the adapter uses when constructing the DSN string. Both "freetds" and "sybase" imply a prefix of "sybase:", which is used for the FreeTDS set of libraries. See also http://www.php.net/manual/en/ref.pdo-dblib.connection.php for more information on the DSN prefixes used in this driver.

### PDO MySQL

- Specify this Adapter to the factory() method with the name 'Pdo_Mysql'.

- This Adapter uses the PHP extensions pdo and pdo_mysql.

- MySQL does not support sequences, so lastInsertId() ignores its arguments and always returns the last value generated for an auto-increment key. The lastSequenceId() method returns `NULL` .

### PDO Oracle

- Specify this Adapter to the factory() method with the name 'Pdo_Oci'.

- This Adapter uses the PHP extensions pdo and pdo_oci.

- Oracle does not support auto-incrementing keys, so you should specify the name of a sequence to lastInsertId() or lastSequenceId() .

### PDO PostgreSQL

- Specify this Adapter to the factory() method with the name 'Pdo_Pgsql'.

- This Adapter uses the PHP extensions pdo and pdo_pgsql.

- PostgreSQL supports both sequences and auto-incrementing keys. Therefore the arguments to lastInsertId() are optional. If you give no arguments, the Adapter returns the last value generated for an auto-increment key. If you give arguments, the Adapter returns the last value generated by the sequence named according to the convention ' table _ column _seq'.

### PDO SQLite

- Specify this Adapter to the factory() method with the name 'Pdo_Sqlite'.

- This Adapter uses the PHP extensions pdo and pdo_sqlite.

- SQLite does not support sequences, so lastInsertId() ignores its arguments and always returns the last value generated for an auto-increment key. The lastSequenceId() method returns `NULL` .

- To connect to an SQLite2 database, specify `'sqlite2'=>true` in the array of parameters when creating an instance of the Pdo_Sqlite Adapter.

- To connect to an in-memory SQLite database, specify `'dbname'=>':memory:'` in the array of parameters when creating an instance of the Pdo_Sqlite Adapter.

- Older versions of the SQLite driver for PHP do not seem to support the PRAGMA commands necessary to ensure that short column names are used in result sets. If you have problems that your result sets are returned with keys of the form "tablename.columnname" when you do a join query, then you should upgrade to the current version of PHP .

### Firebird/Interbase

- This Adapter uses the PHP extension php_interbase.

- Firebird/interbase does not support auto-incrementing keys, so you should specify the name of a sequence to lastInsertId() or lastSequenceId() .

- Currently the `Zend_Db::CASE_FOLDING` option is not supported by the Firebird/interbase adapter. Unquoted identifiers are automatically returned in upper case.

- Adapter name is ZendX_Db_Adapter_Firebird .

  Remember to use the param adapterNamespace with value ZendX_Db_Adapter .

  We recommend to update the gds32.dll (or linux equivalent) bundled with php, to the same version of the server. For Firebird the equivalent gds32.dll is fbclient.dll.

  By default all identifiers (tables names, fields) are returned in upper case.