# Db_RecordExists and Db_NoRecordExists

`Zend_Validate_Db_RecordExists` and `Zend_Validate_Db_NoRecordExists` provide a means to test whether a record exists in a given table of a database, with a given value.

## Basic usage

An example of basic usage of the validators:

    //Check that the email address exists in the database
    $validator = new Zend_Validate_Db_RecordExists(
        array(
            'table' => 'users',
            'field' => 'emailaddress'
        )
    );

    if ($validator->isValid($emailaddress)) {
        // email address appears to be valid
    } else {
        // email address is invalid; print the reasons
        foreach ($validator->getMessages() as $message) {
            echo "$message\n";
        }
    }

The above will test that a given email address is in the database table. If no record is found containing the value of `$emailaddress` in the specified column, then an error message is displayed.

    //Check that the username is not present in the database
    $validator = new Zend_Validate_Db_NoRecordExists(
        array(
            'table' => 'users',
            'field' => 'username'
        )
    );
    if ($validator->isValid($username)) {
        // username appears to be valid
    } else {
        // username is invalid; print the reason
        $messages = $validator->getMessages();
        foreach ($messages as $message) {
            echo "$message\n";
        }
    }

The above will test that a given username is not in the database table. If a record is found containing the value of `$username` in the specified column, then an error message is displayed.

## Excluding records

`Zend_Validate_Db_RecordExists` and `Zend_Validate_Db_NoRecordExists` also provide a means to test the database, excluding a part of the table, either by providing a where clause as a string, or an array with the keys "field" and "value".

When providing an array for the exclude clause, the `!=` operator is used, so you can check the rest of a table for a value before altering a record (for example on a user profile form)

    //Check no other users have the username
    $user_id   = $user->getId();
    $validator = new Zend_Validate_Db_NoRecordExists(
        array(
            'table' => 'users',
            'field' => 'username',
            'exclude' => array(
                'field' => 'id',
                'value' => $user_id
            )
        )
    );

    if ($validator->isValid($username)) {
        // username appears to be valid
    } else {
        // username is invalid; print the reason
        $messages = $validator->getMessages();
        foreach ($messages as $message) {
            echo "$message\n";
        }
    }

The above example will check the table to ensure no records other than the one where `id = $user_id` contains the value $username.

You can also provide a string to the exclude clause so you can use an operator other than `!=`. This can be useful for testing against composite keys.

    $post_id   = $post->getId();
    $clause    = $db->quoteInto('post_id = ?', $category_id);
    $validator = new Zend_Validate_Db_RecordExists(
        array(
            'table'   => 'posts_categories',
            'field'   => 'post_id',
            'exclude' => $clause
        )
    );

    if ($validator->isValid($username)) {
        // username appears to be valid
    } else {
        // username is invalid; print the reason
        $messages = $validator->getMessages();
        foreach ($messages as $message) {
            echo "$message\n";
        }
    }

The above example will check the `posts_categories` table to ensure that a record with the `post_id` has a value matching `$category_id`

## Database Adapters

You can also specify an adapter, as the fourth parameter when instantiating your validator, this will allow you to work with applications using multiple database adapters, or where you have not set a default adapter. As in the example below:

    $validator = new Zend_Validate_Db_RecordExists(
        array(
            'table' => 'users',
            'field' => 'id',
            'adapter' => $dbAdapter
        )
    );

## Database Schemas

You can specify a schema within your database for adapters such as PostgreSQL and DB/2 by simply supplying an array with `table` and `schema` keys. As in the example below:

    $validator = new Zend_Validate_Db_RecordExists(
        array(
            'table'  => 'users',
            'schema' => 'my',
            'field'  => 'id'
        )
    );