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+<?php
+
+/**
+ * @file
+ * Generic Database schema code.
+ */
+
+require_once dirname(__FILE__) . '/query.inc';
+
+/**
+ * @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_revisions 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_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),
+ * 'tnid' => array('type' => 'int', 'unsigned' => TRUE, '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'),
+ * 'tnid' => array('tnid'),
+ * 'translate' => array('translate'),
+ * ),
+ * 'unique keys' => array(
+ * 'vid' => array('vid'),
+ * ),
+ * 'foreign keys' => array(
+ * 'node_revision' => array(
+ * 'table' => 'node_revision',
+ * 'columns' => array('vid' => 'vid'),
+ * ),
+ * 'node_author' => array(
+ * 'table' => 'users',
+ * 'columns' => array('uid' => 'uid'),
+ * ),
+ * ),
+ * 'primary key' => array('nid'),
+ * );
+ * @endcode
+ *
+ * @see drupal_install_schema()
+ */
+
+abstract class DatabaseSchema implements QueryPlaceholderInterface {
+
+ protected $connection;
+
+ /**
+ * The placeholder counter.
+ */
+ protected $placeholder = 0;
+
+ /**
+ * Definition of prefixInfo array structure.
+ *
+ * Rather than redefining DatabaseSchema::getPrefixInfo() for each driver,
+ * by defining the defaultSchema variable only MySQL has to re-write the
+ * method.
+ *
+ * @see DatabaseSchema::getPrefixInfo()
+ */
+ protected $defaultSchema = 'public';
+
+ /**
+ * A unique identifier for this query object.
+ */
+ protected $uniqueIdentifier;
+
+ public function __construct($connection) {
+ $this->uniqueIdentifier = uniqid('', TRUE);
+ $this->connection = $connection;
+ }
+
+ /**
+ * Implements the magic __clone function.
+ */
+ public function __clone() {
+ $this->uniqueIdentifier = uniqid('', TRUE);
+ }
+
+ /**
+ * Implements QueryPlaceHolderInterface::uniqueIdentifier().
+ */
+ public function uniqueIdentifier() {
+ return $this->uniqueIdentifier;
+ }
+
+ /**
+ * Implements QueryPlaceHolderInterface::nextPlaceholder().
+ */
+ public function nextPlaceholder() {
+ return $this->placeholder++;
+ }
+
+ /**
+ * Get information about the table name and schema from the prefix.
+ *
+ * @param
+ * Name of table to look prefix up for. Defaults to 'default' because thats
+ * default key for prefix.
+ * @param $add_prefix
+ * Boolean that indicates whether the given table name should be prefixed.
+ *
+ * @return
+ * A keyed array with information about the schema, table name and prefix.
+ */
+ protected function getPrefixInfo($table = 'default', $add_prefix = TRUE) {
+ $info = array(
+ 'schema' => $this->defaultSchema,
+ 'prefix' => $this->connection->tablePrefix($table),
+ );
+ if ($add_prefix) {
+ $table = $info['prefix'] . $table;
+ }
+ // If the prefix contains a period in it, then that means the prefix also
+ // contains a schema reference in which case we will change the schema key
+ // to the value before the period in the prefix. Everything after the dot
+ // will be prefixed onto the front of the table.
+ if (($pos = strpos($table, '.')) !== FALSE) {
+ // Grab everything before the period.
+ $info['schema'] = substr($table, 0, $pos);
+ // Grab everything after the dot.
+ $info['table'] = substr($table, ++$pos);
+ }
+ else {
+ $info['table'] = $table;
+ }
+ return $info;
+ }
+
+ /**
+ * Create names for indexes, primary keys and constraints.
+ *
+ * This prevents using {} around non-table names like indexes and keys.
+ */
+ function prefixNonTable($table) {
+ $args = func_get_args();
+ $info = $this->getPrefixInfo($table);
+ $args[0] = $info['table'];
+ return implode('_', $args);
+ }
+
+ /**
+ * Build a condition to match a table name against a standard information_schema.
+ *
+ * The information_schema is a SQL standard that provides information about the
+ * database server and the databases, schemas, tables, columns and users within
+ * it. This makes information_schema a useful tool to use across the drupal
+ * database drivers and is used by a few different functions. The function below
+ * describes the conditions to be meet when querying information_schema.tables
+ * for drupal tables or information associated with drupal tables. Even though
+ * this is the standard method, not all databases follow standards and so this
+ * method should be overwritten by a database driver if the database provider
+ * uses alternate methods. Because information_schema.tables is used in a few
+ * different functions, a database driver will only need to override this function
+ * to make all the others work. For example see includes/databases/mysql/schema.inc.
+ *
+ * @param $table_name
+ * The name of the table in question.
+ * @param $operator
+ * The operator to apply on the 'table' part of the condition.
+ * @param $add_prefix
+ * Boolean to indicate whether the table name needs to be prefixed.
+ *
+ * @return QueryConditionInterface
+ * A DatabaseCondition object.
+ */
+ protected function buildTableNameCondition($table_name, $operator = '=', $add_prefix = TRUE) {
+ $info = $this->connection->getConnectionOptions();
+
+ // Retrive the table name and schema
+ $table_info = $this->getPrefixInfo($table_name, $add_prefix);
+
+ $condition = new DatabaseCondition('AND');
+ $condition->condition('table_catalog', $info['database']);
+ $condition->condition('table_schema', $table_info['schema']);
+ $condition->condition('table_name', $table_info['table'], $operator);
+ return $condition;
+ }
+
+ /**
+ * Check if a table exists.
+ *
+ * @param $table
+ * The name of the table in drupal (no prefixing).
+ *
+ * @return
+ * TRUE if the given table exists, otherwise FALSE.
+ */
+ public function tableExists($table) {
+ $condition = $this->buildTableNameCondition($table);
+ $condition->compile($this->connection, $this);
+ // Normally, we would heartily discourage the use of string
+ // concatenation for conditionals like this however, we
+ // couldn't use db_select() here because it would prefix
+ // information_schema.tables and the query would fail.
+ // Don't use {} around information_schema.tables table.
+ return (bool) $this->connection->query("SELECT 1 FROM information_schema.tables WHERE " . (string) $condition, $condition->arguments())->fetchField();
+ }
+
+ /**
+ * Find all tables that are like the specified base table name.
+ *
+ * @param $table_expression
+ * An SQL expression, for example "simpletest%" (without the quotes).
+ * BEWARE: this is not prefixed, the caller should take care of that.
+ *
+ * @return
+ * Array, both the keys and the values are the matching tables.
+ */
+ public function findTables($table_expression) {
+ $condition = $this->buildTableNameCondition($table_expression, 'LIKE', FALSE);
+
+ $condition->compile($this->connection, $this);
+ // Normally, we would heartily discourage the use of string
+ // concatenation for conditionals like this however, we
+ // couldn't use db_select() here because it would prefix
+ // information_schema.tables and the query would fail.
+ // Don't use {} around information_schema.tables table.
+ return $this->connection->query("SELECT table_name FROM information_schema.tables WHERE " . (string) $condition, $condition->arguments())->fetchAllKeyed(0, 0);
+ }
+
+ /**
+ * Check if a column exists in the given table.
+ *
+ * @param $table
+ * The name of the table in drupal (no prefixing).
+ * @param $name
+ * The name of the column.
+ *
+ * @return
+ * TRUE if the given column exists, otherwise FALSE.
+ */
+ public function fieldExists($table, $column) {
+ $condition = $this->buildTableNameCondition($table);
+ $condition->condition('column_name', $column);
+ $condition->compile($this->connection, $this);
+ // Normally, we would heartily discourage the use of string
+ // concatenation for conditionals like this however, we
+ // couldn't use db_select() here because it would prefix
+ // information_schema.tables and the query would fail.
+ // Don't use {} around information_schema.columns table.
+ return (bool) $this->connection->query("SELECT 1 FROM information_schema.columns WHERE " . (string) $condition, $condition->arguments())->fetchField();
+ }
+
+ /**
+ * Returns a mapping of Drupal schema field names to DB-native field types.
+ *
+ * Because different field types do not map 1:1 between databases, Drupal has
+ * its own normalized field type names. This function returns a driver-specific
+ * mapping table from Drupal names to the native names for each database.
+ *
+ * @return array
+ * An array of Schema API field types to driver-specific field types.
+ */
+ abstract public function getFieldTypeMap();
+
+ /**
+ * Rename a table.
+ *
+ * @param $table
+ * The table to be renamed.
+ * @param $new_name
+ * The new name for the table.
+ *
+ * @throws DatabaseSchemaObjectDoesNotExistException
+ * If the specified table doesn't exist.
+ * @throws DatabaseSchemaObjectExistsException
+ * If a table with the specified new name already exists.
+ */
+ abstract public function renameTable($table, $new_name);
+
+ /**
+ * Drop a table.
+ *
+ * @param $table
+ * The table to be dropped.
+ *
+ * @return
+ * TRUE if the table was successfully dropped, FALSE if there was no table
+ * by that name to begin with.
+ */
+ abstract public function dropTable($table);
+
+ /**
+ * Add a new field to a table.
+ *
+ * @param $table
+ * Name of the table to be altered.
+ * @param $field
+ * Name of the field to be added.
+ * @param $spec
+ * The field specification array, as taken from a schema definition.
+ * The specification may also contain the key 'initial', the newly
+ * created field will be set to the value of the key in all rows.
+ * This is most useful for creating NOT NULL columns with no default
+ * value in existing tables.
+ * @param $keys_new
+ * Optional keys and indexes specification to be created on the
+ * table along with adding the field. The format is the same as a
+ * table specification but without the 'fields' element. If you are
+ * adding a type 'serial' field, you MUST specify at least one key
+ * or index including it in this array. See db_change_field() for more
+ * explanation why.
+ *
+ * @throws DatabaseSchemaObjectDoesNotExistException
+ * If the specified table doesn't exist.
+ * @throws DatabaseSchemaObjectExistsException
+ * If the specified table already has a field by that name.
+ */
+ abstract public function addField($table, $field, $spec, $keys_new = array());
+
+ /**
+ * Drop a field.
+ *
+ * @param $table
+ * The table to be altered.
+ * @param $field
+ * The field to be dropped.
+ *
+ * @return
+ * TRUE if the field was successfully dropped, FALSE if there was no field
+ * by that name to begin with.
+ */
+ abstract public function dropField($table, $field);
+
+ /**
+ * Set the default value for a field.
+ *
+ * @param $table
+ * The table to be altered.
+ * @param $field
+ * The field to be altered.
+ * @param $default
+ * Default value to be set. NULL for 'default NULL'.
+ *
+ * @throws DatabaseSchemaObjectDoesNotExistException
+ * If the specified table or field doesn't exist.
+ */
+ abstract public function fieldSetDefault($table, $field, $default);
+
+ /**
+ * Set a field to have no default value.
+ *
+ * @param $table
+ * The table to be altered.
+ * @param $field
+ * The field to be altered.
+ *
+ * @throws DatabaseSchemaObjectDoesNotExistException
+ * If the specified table or field doesn't exist.
+ */
+ abstract public function fieldSetNoDefault($table, $field);
+
+ /**
+ * Checks if an index exists in the given table.
+ *
+ * @param $table
+ * The name of the table in drupal (no prefixing).
+ * @param $name
+ * The name of the index in drupal (no prefixing).
+ *
+ * @return
+ * TRUE if the given index exists, otherwise FALSE.
+ */
+ abstract public function indexExists($table, $name);
+
+ /**
+ * Add a primary key.
+ *
+ * @param $table
+ * The table to be altered.
+ * @param $fields
+ * Fields for the primary key.
+ *
+ * @throws DatabaseSchemaObjectDoesNotExistException
+ * If the specified table doesn't exist.
+ * @throws DatabaseSchemaObjectExistsException
+ * If the specified table already has a primary key.
+ */
+ abstract public function addPrimaryKey($table, $fields);
+
+ /**
+ * Drop the primary key.
+ *
+ * @param $table
+ * The table to be altered.
+ *
+ * @return
+ * TRUE if the primary key was successfully dropped, FALSE if there was no
+ * primary key on this table to begin with.
+ */
+ abstract public function dropPrimaryKey($table);
+
+ /**
+ * Add a unique key.
+ *
+ * @param $table
+ * The table to be altered.
+ * @param $name
+ * The name of the key.
+ * @param $fields
+ * An array of field names.
+ *
+ * @throws DatabaseSchemaObjectDoesNotExistException
+ * If the specified table doesn't exist.
+ * @throws DatabaseSchemaObjectExistsException
+ * If the specified table already has a key by that name.
+ */
+ abstract public function addUniqueKey($table, $name, $fields);
+
+ /**
+ * Drop a unique key.
+ *
+ * @param $table
+ * The table to be altered.
+ * @param $name
+ * The name of the key.
+ *
+ * @return
+ * TRUE if the key was successfully dropped, FALSE if there was no key by
+ * that name to begin with.
+ */
+ abstract public function dropUniqueKey($table, $name);
+
+ /**
+ * Add an index.
+ *
+ * @param $table
+ * The table to be altered.
+ * @param $name
+ * The name of the index.
+ * @param $fields
+ * An array of field names.
+ *
+ * @throws DatabaseSchemaObjectDoesNotExistException
+ * If the specified table doesn't exist.
+ * @throws DatabaseSchemaObjectExistsException
+ * If the specified table already has an index by that name.
+ */
+ abstract public function addIndex($table, $name, $fields);
+
+ /**
+ * Drop an index.
+ *
+ * @param $table
+ * The table to be altered.
+ * @param $name
+ * The name of the index.
+ *
+ * @return
+ * TRUE if the index was successfully dropped, FALSE if there was no index
+ * by that name to begin with.
+ */
+ abstract public function dropIndex($table, $name);
+
+ /**
+ * Change a field definition.
+ *
+ * IMPORTANT NOTE: To maintain database portability, you have to explicitly
+ * recreate all indices and primary keys that are using the changed field.
+ *
+ * That means that you have to drop all affected keys and indexes with
+ * db_drop_{primary_key,unique_key,index}() before calling db_change_field().
+ * To recreate the keys and indices, pass the key definitions as the
+ * optional $keys_new argument directly to db_change_field().
+ *
+ * For example, suppose you have:
+ * @code
+ * $schema['foo'] = array(
+ * 'fields' => array(
+ * 'bar' => array('type' => 'int', 'not null' => TRUE)
+ * ),
+ * 'primary key' => array('bar')
+ * );
+ * @endcode
+ * and you want to change foo.bar to be type serial, leaving it as the
+ * primary key. The correct sequence is:
+ * @code
+ * db_drop_primary_key('foo');
+ * db_change_field('foo', 'bar', 'bar',
+ * array('type' => 'serial', 'not null' => TRUE),
+ * array('primary key' => array('bar')));
+ * @endcode
+ *
+ * The reasons for this are due to the different database engines:
+ *
+ * On PostgreSQL, changing a field definition involves adding a new field
+ * and dropping an old one which* causes any indices, primary keys and
+ * sequences (from serial-type fields) that use the changed field to be dropped.
+ *
+ * On MySQL, all type 'serial' fields must be part of at least one key
+ * or index as soon as they are created. You cannot use
+ * db_add_{primary_key,unique_key,index}() for this purpose because
+ * the ALTER TABLE command will fail to add the column without a key
+ * or index specification. The solution is to use the optional
+ * $keys_new argument to create the key or index at the same time as
+ * field.
+ *
+ * You could use db_add_{primary_key,unique_key,index}() in all cases
+ * unless you are converting a field to be type serial. You can use
+ * the $keys_new argument in all cases.
+ *
+ * @param $table
+ * Name of the table.
+ * @param $field
+ * Name of the field to change.
+ * @param $field_new
+ * New name for the field (set to the same as $field if you don't want to change the name).
+ * @param $spec
+ * The field specification for the new field.
+ * @param $keys_new
+ * Optional keys and indexes specification to be created on the
+ * table along with changing the field. The format is the same as a
+ * table specification but without the 'fields' element.
+ *
+ * @throws DatabaseSchemaObjectDoesNotExistException
+ * If the specified table or source field doesn't exist.
+ * @throws DatabaseSchemaObjectExistsException
+ * If the specified destination field already exists.
+ */
+ abstract public function changeField($table, $field, $field_new, $spec, $keys_new = array());
+
+ /**
+ * Create a new table from a Drupal table definition.
+ *
+ * @param $name
+ * The name of the table to create.
+ * @param $table
+ * A Schema API table definition array.
+ *
+ * @throws DatabaseSchemaObjectExistsException
+ * If the specified table already exists.
+ */
+ public function createTable($name, $table) {
+ if ($this->tableExists($name)) {
+ throw new DatabaseSchemaObjectExistsException(t('Table %name already exists.', array('%name' => $name)));
+ }
+ $statements = $this->createTableSql($name, $table);
+ foreach ($statements as $statement) {
+ $this->connection->query($statement);
+ }
+ }
+
+ /**
+ * Return an array of field names from an array of key/index column specifiers.
+ *
+ * This is usually an identity function but if a key/index uses a column prefix
+ * specification, this function extracts just the name.
+ *
+ * @param $fields
+ * An array of key/index column specifiers.
+ *
+ * @return
+ * An array of field names.
+ */
+ public function fieldNames($fields) {
+ $return = array();
+ foreach ($fields as $field) {
+ if (is_array($field)) {
+ $return[] = $field[0];
+ }
+ else {
+ $return[] = $field;
+ }
+ }
+ return $return;
+ }
+
+ /**
+ * Prepare a table or column comment for database query.
+ *
+ * @param $comment
+ * The comment string to prepare.
+ * @param $length
+ * Optional upper limit on the returned string length.
+ *
+ * @return
+ * The prepared comment.
+ */
+ public function prepareComment($comment, $length = NULL) {
+ return $this->connection->quote($comment);
+ }
+}
+
+/**
+ * Exception thrown if an object being created already exists.
+ *
+ * For example, this exception should be thrown whenever there is an attempt to
+ * create a new database table, field, or index that already exists in the
+ * database schema.
+ */
+class DatabaseSchemaObjectExistsException extends Exception {}
+
+/**
+ * Exception thrown if an object being modified doesn't exist yet.
+ *
+ * For example, this exception should be thrown whenever there is an attempt to
+ * modify a database table, field, or index that does not currently exist in
+ * the database schema.
+ */
+class DatabaseSchemaObjectDoesNotExistException extends Exception {}
+
+/**
+ * @} End of "defgroup schemaapi".
+ */
+