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drupal/core/modules/system/database.api.php

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<?php
/**
* @file
* Hooks related to the Database system and the Schema API.
*/
/**
* @defgroup database Database abstraction layer
* @{
* Allow the use of different database servers using the same code base.
*
* @section sec_intro Overview
* Drupal's database abstraction layer provides a unified database query API
* that can query different underlying databases. It is built upon PHP's
* PDO (PHP Data Objects) database API, and inherits much of its syntax and
* semantics. Besides providing a unified API for database queries, the
* database abstraction layer also provides a structured way to construct
* complex queries, and it protects the database by using good security
* practices.
*
* For more detailed information on the database abstraction layer, see
* https://drupal.org/developing/api/database
*
* @section sec_entity Querying entities
* Any query on Drupal entities or fields should use the Entity Query API. See
* the @link entity_api entity API topic @endlink for more information.
*
* @section sec_simple Simple SELECT database queries
* For simple SELECT queries that do not involve entities, the Drupal database
* abstraction layer provides the functions db_query() and db_query_range(),
* which execute SELECT queries (optionally with range limits) and return result
* sets that you can iterate over using foreach loops. (The result sets are
* objects implementing the \Drupal\Core\Database\StatementInterface interface.)
* You can use the simple query functions for query strings that are not
* dynamic (except for placeholders, see below), and that you are certain will
* work in any database engine. See @ref sec_dynamic below if you have a more
* complex query, or a query whose syntax would be different in some databases.
*
* As a note, db_query() and similar functions are wrappers on connection object
* methods. In most classes, you should use dependency injection and the
* database connection object instead of these wrappers; See @ref sec_connection
* below for details.
*
* To use the simple database query functions, you will need to make a couple of
* modifications to your bare SQL query:
* - Enclose your table name in {}. Drupal allows site builders to use
* database table name prefixes, so you cannot be sure what the actual
* name of the table will be. So, use the name that is in the hook_schema(),
* enclosed in {}, and Drupal will calculate the right name.
* - Instead of putting values for conditions into the query, use placeholders.
* The placeholders are named and start with :, and they take the place of
* putting variables directly into the query, to protect against SQL
* injection attacks.
* - LIMIT syntax differs between databases, so if you have a ranged query,
* use db_query_range() instead of db_query().
*
* For example, if the query you want to run is:
* @code
* SELECT e.id, e.title, e.created FROM example e WHERE e.uid = $uid
* ORDER BY e.created DESC LIMIT 0, 10;
* @endcode
* you would do it like this:
* @code
* $result = db_query_range('SELECT e.id, e.title, e.created
* FROM {example} e
* WHERE e.uid = :uid
* ORDER BY e.created DESC',
* 0, 10, array(':uid' => $uid));
* foreach ($result as $record) {
* // Perform operations on $record->title, etc. here.
* }
* @endcode
*
* Note that if your query has a string condition, like:
* @code
* WHERE e.my_field = 'foo'
* @endcode
* when you convert it to placeholders, omit the quotes:
* @code
* WHERE e.my_field = :my_field
* ... array(':my_field' => 'foo') ...
* @endcode
*
* @section sec_dynamic Dynamic SELECT queries
* For SELECT queries where the simple query API described in @ref sec_simple
* will not work well, you need to use the dynamic query API. However, you
* should still use the Entity Query API if your query involves entities or
* fields (see the @link entity_api Entity API topic @endlink for more on
* entity queries).
*
* As a note, db_select() and similar functions are wrappers on connection
* object methods. In most classes, you should use dependency injection and the
* database connection object instead of these wrappers; See @ref sec_connection
* below for details.
*
* The dynamic query API lets you build up a query dynamically using method
* calls. As an illustration, the query example from @ref sec_simple above
* would be:
* @code
* $result = db_select('example', 'e')
* ->fields('e', array('id', 'title', 'created'))
* ->condition('e.uid', $uid)
* ->orderBy('e.created', 'DESC')
* ->range(0, 10)
* ->execute();
* @endcode
*
* There are also methods to join to other tables, add fields with aliases,
* isNull() to have a @code WHERE e.foo IS NULL @endcode condition, etc. See
* https://drupal.org/developing/api/database for many more details.
*
* One note on chaining: It is common in the dynamic database API to chain
* method calls (as illustrated here), because most of the query methods modify
* the query object and then return the modified query as their return
* value. However, there are some important exceptions; these methods (and some
* others) do not support chaining:
* - join(), innerJoin(), etc.: These methods return the joined table alias.
* - addField(): This method returns the field alias.
* Check the documentation for the query method you are using to see if it
* returns the query or something else, and only chain methods that return the
* query.
*
* @section_insert INSERT, UPDATE, and DELETE queries
* INSERT, UPDATE, and DELETE queries need special care in order to behave
* consistently across databases; you should never use db_query() to run
* an INSERT, UPDATE, or DELETE query. Instead, use functions db_insert(),
* db_update(), and db_delete() to obtain a base query on your table, and then
* add dynamic conditions (as illustrated in @ref sec_dynamic above).
*
* As a note, db_insert() and similar functions are wrappers on connection
* object methods. In most classes, you should use dependency injection and the
* database connection object instead of these wrappers; See @ref sec_connection
* below for details.
*
* For example, if your query is:
* @code
* INSERT INTO example (id, uid, path, name) VALUES (1, 2, 'path', 'Name');
* @endcode
* You can execute it via:
* @code
* $fields = array('id' => 1, 'uid' => 2, 'path' => 'path', 'name' => 'Name');
* db_insert('example')
* ->fields($fields)
* ->execute();
* @endcode
*
* @section sec_transaction Transactions
* Drupal supports transactions, including a transparent fallback for
* databases that do not support transactions. To start a new transaction,
* call @code $txn = db_transaction(); @endcode The transaction will
* remain open for as long as the variable $txn remains in scope; when $txn is
* destroyed, the transaction will be committed. If your transaction is nested
* inside of another then Drupal will track each transaction and only commit
* the outer-most transaction when the last transaction object goes out out of
* scope (when all relevant queries have completed successfully).
*
* Example:
* @code
* function my_transaction_function() {
* // The transaction opens here.
* $txn = db_transaction();
*
* try {
* $id = db_insert('example')
* ->fields(array(
* 'field1' => 'mystring',
* 'field2' => 5,
* ))
* ->execute();
*
* my_other_function($id);
*
* return $id;
* }
* catch (Exception $e) {
* // Something went wrong somewhere, so roll back now.
* $txn->rollback();
* // Log the exception to watchdog.
* watchdog_exception('type', $e);
* }
*
* // $txn goes out of scope here. Unless the transaction was rolled back, it
* // gets automatically committed here.
* }
*
* function my_other_function($id) {
* // The transaction is still open here.
*
* if ($id % 2 == 0) {
* db_update('example')
* ->condition('id', $id)
* ->fields(array('field2' => 10))
* ->execute();
* }
* }
* @endcode
*
* @section sec_connection Database connection objects
* The examples here all use functions like db_select() and db_query(), which
* can be called from any Drupal method or function code. In some classes, you
* may already have a database connection object in a member variable, or it may
* be passed into a class constructor via dependency injection. If that is the
* case, you can look at the code for db_select() and the other functions to see
* how to get a query object from your connection variable. For example:
* @code
* $query = $connection->select('example', 'e');
* @endcode
* would be the equivalent of
* @code
* $query = db_select('example', 'e');
* @endcode
* if you had a connection object variable $connection available to use. See
* also the @link container Services and Dependency Injection topic. @endlink
*
* @see http://drupal.org/developing/api/database
* @see entity_api
* @see schemaapi
*
* @}
*/
/**
* @defgroup schemaapi Schema API
* @{
* API to handle database schemas.
*
* A Drupal schema definition is an array structure representing one or
* more tables and their related keys and indexes. A schema is defined by
* hook_schema(), which usually lives in a modulename.install file.
*
* By implementing hook_schema() and specifying the tables your module
* declares, you can easily create and drop these tables on all
* supported database engines. You don't have to deal with the
* different SQL dialects for table creation and alteration of the
* supported database engines.
*
* hook_schema() should return an array with a key for each table that
* the module defines.
*
* The following keys are defined:
* - 'description': A string in non-markup plain text describing this table
* and its purpose. References to other tables should be enclosed in
* curly-brackets. For example, the node_field_revision table
* description field might contain "Stores per-revision title and
* body data for each {node}."
* - 'fields': An associative array ('fieldname' => specification)
* that describes the table's database columns. The specification
* is also an array. The following specification parameters are defined:
* - 'description': A string in non-markup plain text describing this field
* and its purpose. References to other tables should be enclosed in
* curly-brackets. For example, the node table vid field
* description might contain "Always holds the largest (most
* recent) {node_field_revision}.vid value for this nid."
* - 'type': The generic datatype: 'char', 'varchar', 'text', 'blob', 'int',
* 'float', 'numeric', or 'serial'. Most types just map to the according
* database engine specific datatypes. Use 'serial' for auto incrementing
* fields. This will expand to 'INT auto_increment' on MySQL.
* - 'mysql_type', 'pgsql_type', 'sqlite_type', etc.: If you need to
* use a record type not included in the officially supported list
* of types above, you can specify a type for each database
* backend. In this case, you can leave out the type parameter,
* but be advised that your schema will fail to load on backends that
* do not have a type specified. A possible solution can be to
* use the "text" type as a fallback.
* - 'serialize': A boolean indicating whether the field will be stored as
* a serialized string.
* - 'size': The data size: 'tiny', 'small', 'medium', 'normal',
* 'big'. This is a hint about the largest value the field will
* store and determines which of the database engine specific
* datatypes will be used (e.g. on MySQL, TINYINT vs. INT vs. BIGINT).
* 'normal', the default, selects the base type (e.g. on MySQL,
* INT, VARCHAR, BLOB, etc.).
* Not all sizes are available for all data types. See
* DatabaseSchema::getFieldTypeMap() for possible combinations.
* - 'not null': If true, no NULL values will be allowed in this
* database column. Defaults to false.
* - 'default': The field's default value. The PHP type of the
* value matters: '', '0', and 0 are all different. If you
* specify '0' as the default value for a type 'int' field it
* will not work because '0' is a string containing the
* character "zero", not an integer.
* - 'length': The maximal length of a type 'char', 'varchar' or 'text'
* field. Ignored for other field types.
* - 'unsigned': A boolean indicating whether a type 'int', 'float'
* and 'numeric' only is signed or unsigned. Defaults to
* FALSE. Ignored for other field types.
* - 'precision', 'scale': For type 'numeric' fields, indicates
* the precision (total number of significant digits) and scale
* (decimal digits right of the decimal point). Both values are
* mandatory. Ignored for other field types.
* - 'binary': A boolean indicating that MySQL should force 'char',
* 'varchar' or 'text' fields to use case-sensitive binary collation.
* This has no effect on other database types for which case sensitivity
* is already the default behavior.
* All parameters apart from 'type' are optional except that type
* 'numeric' columns must specify 'precision' and 'scale', and type
* 'varchar' must specify the 'length' parameter.
* - 'primary key': An array of one or more key column specifiers (see below)
* that form the primary key.
* - 'unique keys': An associative array of unique keys ('keyname' =>
* specification). Each specification is an array of one or more
* key column specifiers (see below) that form a unique key on the table.
* - 'foreign keys': An associative array of relations ('my_relation' =>
* specification). Each specification is an array containing the name of
* the referenced table ('table'), and an array of column mappings
* ('columns'). Column mappings are defined by key pairs ('source_column' =>
* 'referenced_column').
* - 'indexes': An associative array of indexes ('indexname' =>
* specification). Each specification is an array of one or more
* key column specifiers (see below) that form an index on the
* table.
*
* A key column specifier is either a string naming a column or an
* array of two elements, column name and length, specifying a prefix
* of the named column.
*
* As an example, here is a SUBSET of the schema definition for
* Drupal's 'node' table. It show four fields (nid, vid, type, and
* title), the primary key on field 'nid', a unique key named 'vid' on
* field 'vid', and two indexes, one named 'nid' on field 'nid' and
* one named 'node_title_type' on the field 'title' and the first four
* bytes of the field 'type':
*
* @code
* $schema['node'] = array(
* 'description' => 'The base table for nodes.',
* 'fields' => array(
* 'nid' => array('type' => 'serial', 'unsigned' => TRUE, 'not null' => TRUE),
* 'vid' => array('type' => 'int', 'unsigned' => TRUE, 'not null' => TRUE,'default' => 0),
* 'type' => array('type' => 'varchar','length' => 32,'not null' => TRUE, 'default' => ''),
* 'language' => array('type' => 'varchar','length' => 12,'not null' => TRUE,'default' => ''),
* 'title' => array('type' => 'varchar','length' => 255,'not null' => TRUE, 'default' => ''),
* 'uid' => array('type' => 'int', 'not null' => TRUE, 'default' => 0),
* 'status' => array('type' => 'int', 'not null' => TRUE, 'default' => 1),
* 'created' => array('type' => 'int', 'not null' => TRUE, 'default' => 0),
* 'changed' => array('type' => 'int', 'not null' => TRUE, 'default' => 0),
* 'comment' => array('type' => 'int', 'not null' => TRUE, 'default' => 0),
* 'promote' => array('type' => 'int', 'not null' => TRUE, 'default' => 0),
* 'moderate' => array('type' => 'int', 'not null' => TRUE,'default' => 0),
* 'sticky' => array('type' => 'int', 'not null' => TRUE, 'default' => 0),
* 'translate' => array('type' => 'int', 'not null' => TRUE, 'default' => 0),
* ),
* 'indexes' => array(
* 'node_changed' => array('changed'),
* 'node_created' => array('created'),
* 'node_moderate' => array('moderate'),
* 'node_frontpage' => array('promote', 'status', 'sticky', 'created'),
* 'node_status_type' => array('status', 'type', 'nid'),
* 'node_title_type' => array('title', array('type', 4)),
* 'node_type' => array(array('type', 4)),
* 'uid' => array('uid'),
* 'translate' => array('translate'),
* ),
* 'unique keys' => array(
* 'vid' => array('vid'),
* ),
* 'foreign keys' => array(
* 'node_revision' => array(
* 'table' => 'node_field_revision',
* 'columns' => array('vid' => 'vid'),
* ),
* 'node_author' => array(
* 'table' => 'users',
* 'columns' => array('uid' => 'uid'),
* ),
* ),
* 'primary key' => array('nid'),
* );
* @endcode
*
* @see drupal_install_schema()
*
* @}
*/
/**
* @addtogroup hooks
* @{
*/
/**
* Perform alterations to a structured query.
*
* Structured (aka dynamic) queries that have tags associated may be altered by any module
* before the query is executed.
*
* @param $query
* A Query object describing the composite parts of a SQL query.
*
* @see hook_query_TAG_alter()
* @see node_query_node_access_alter()
* @see AlterableInterface
* @see SelectInterface
*
* @ingroup database
*/
function hook_query_alter(Drupal\Core\Database\Query\AlterableInterface $query) {
if ($query->hasTag('micro_limit')) {
$query->range(0, 2);
}
}
/**
* Perform alterations to a structured query for a given tag.
*
* @param $query
* An Query object describing the composite parts of a SQL query.
*
* @see hook_query_alter()
* @see node_query_node_access_alter()
* @see AlterableInterface
* @see SelectInterface
*
* @ingroup database
*/
function hook_query_TAG_alter(Drupal\Core\Database\Query\AlterableInterface $query) {
// Skip the extra expensive alterations if site has no node access control modules.
if (!node_access_view_all_nodes()) {
// Prevent duplicates records.
$query->distinct();
// The recognized operations are 'view', 'update', 'delete'.
if (!$op = $query->getMetaData('op')) {
$op = 'view';
}
// Skip the extra joins and conditions for node admins.
if (!\Drupal::currentUser()->hasPermission('bypass node access')) {
// The node_access table has the access grants for any given node.
$access_alias = $query->join('node_access', 'na', '%alias.nid = n.nid');
$or = db_or();
// If any grant exists for the specified user, then user has access to the node for the specified operation.
foreach (node_access_grants($op, $query->getMetaData('account')) as $realm => $gids) {
foreach ($gids as $gid) {
$or->condition(db_and()
->condition($access_alias . '.gid', $gid)
->condition($access_alias . '.realm', $realm)
);
}
}
if (count($or->conditions())) {
$query->condition($or);
}
$query->condition($access_alias . 'grant_' . $op, 1, '>=');
}
}
}
/**
* Define the current version of the database schema.
*
* A Drupal schema definition is an array structure representing one or more
* tables and their related keys and indexes. A schema is defined by
* hook_schema() which must live in your module's .install file.
*
* The tables declared by this hook will be automatically created when the
* module is installed, and removed when the module is uninstalled. This happens
* before hook_install() is invoked, and after hook_uninstall() is invoked,
* respectively.
*
* By declaring the tables used by your module via an implementation of
* hook_schema(), these tables will be available on all supported database
* engines. You don't have to deal with the different SQL dialects for table
* creation and alteration of the supported database engines.
*
* See the Schema API Handbook at http://drupal.org/node/146843 for details on
* schema definition structures.
*
* @return array
* A schema definition structure array. For each element of the
* array, the key is a table name and the value is a table structure
* definition.
*
* @see hook_schema_alter()
*
* @ingroup schemaapi
*/
function hook_schema() {
$schema['node'] = array(
// Example (partial) specification for table "node".
'description' => 'The base table for nodes.',
'fields' => array(
'nid' => array(
'description' => 'The primary identifier for a node.',
'type' => 'serial',
'unsigned' => TRUE,
'not null' => TRUE,
),
'vid' => array(
'description' => 'The current {node_field_revision}.vid version identifier.',
'type' => 'int',
'unsigned' => TRUE,
'not null' => TRUE,
'default' => 0,
),
'type' => array(
'description' => 'The type of this node.',
'type' => 'varchar',
'length' => 32,
'not null' => TRUE,
'default' => '',
),
'title' => array(
'description' => 'The node title.',
'type' => 'varchar',
'length' => 255,
'not null' => TRUE,
'default' => '',
),
),
'indexes' => array(
'node_changed' => array('changed'),
'node_created' => array('created'),
),
'unique keys' => array(
'nid_vid' => array('nid', 'vid'),
'vid' => array('vid'),
),
'foreign keys' => array(
'node_revision' => array(
'table' => 'node_field_revision',
'columns' => array('vid' => 'vid'),
),
'node_author' => array(
'table' => 'users',
'columns' => array('uid' => 'uid'),
),
),
'primary key' => array('nid'),
);
return $schema;
}
/**
* Perform alterations to existing database schemas.
*
* When a module modifies the database structure of another module (by
* changing, adding or removing fields, keys or indexes), it should
* implement hook_schema_alter() to update the default $schema to take its
* changes into account.
*
* See hook_schema() for details on the schema definition structure.
*
* @param $schema
* Nested array describing the schemas for all modules.
*
* @ingroup schemaapi
*/
function hook_schema_alter(&$schema) {
// Add field to existing schema.
$schema['users']['fields']['timezone_id'] = array(
'type' => 'int',
'not null' => TRUE,
'default' => 0,
'description' => 'Per-user timezone configuration.',
);
}
/**
* @} End of "addtogroup hooks".
*/
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