<?php
/**
 * DataTables PHP libraries.
 *
 * PHP libraries for DataTables and DataTables Editor, utilising PHP 5.3+.
 *
 *  @author    SpryMedia
 *  @copyright 2012 SpryMedia ( http://sprymedia.co.uk )
 *  @license   http://editor.datatables.net/license DataTables Editor
 *  @link      http://editor.datatables.net
 */

namespace DataTables\Editor;
if (!defined('DATATABLES')) exit();

use
	DataTables,
	DataTables\Editor,
	DataTables\Editor\Field;


/**
 * Join table class for DataTables Editor.
 *
 * The Join class can be used with {@see Editor->join()} to allow Editor to
 * obtain joined information from the database.
 *
 * For an overview of how Join tables work, please refer to the 
 * {@link https://editor.datatables.net/manual/php/ Editor manual} as it is
 * useful to understand how this class represents the links between tables, 
 * before fully getting to grips with it's API.
 *
 *  @example
 *    Join the parent table (the one specified in the {@see Editor->table()}
 *    method) with the table *access*, with a link table *user__access*, which
 *    allows multiple properties to be found for each row in the parent table.
 *    ```php
 *      Join::inst( 'access', 'array' )
 *          ->link( 'users.id', 'user_access.user_id' )
 *          ->link( 'access.id', 'user_access.access_id' )
 *          ->field(
 *              Field::inst( 'id' )->validator( 'Validate::required' ),
 *              Field::inst( 'name' )
 *          )
 *    ```
 *
 *  @example
 *    Single row join - here we join the parent table with a single row in
 *    the child table, without an intermediate link table. In this case the
 *    child table is called *extra* and the two fields give the columns that
 *    Editor will read from that table.
 *    ```php
 *        Join::inst( 'extra', 'object' )
 *            ->link( 'user.id', 'extra.user_id' )
 *            ->field(
 *                Field::inst( 'comments' ),
 *                Field::inst( 'review' )
 *            )
 *    ```
 */
class Join extends DataTables\Ext {
	/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
	 * Constructor
	 */

	/**
	 * Join instance constructor.
	 *  @param string $table Table name to get the joined data from.
	 *  @param string $type Work with a single result ('object') or an array of 
	 *    results ('array') for the join.
	 */
	function __construct( $table=null, $type='object' )
	{
		$this->table( $table );
		$this->type( $type );
	}


	/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
	 * Private properties
	 */

	/** @var DataTables\Editor\Field[] */
	private $_fields = array();

	/** @var array */
	private $_join = array(
		"parent" => null,
		"child" => null,
		"table" => null
	);

	/**	@var array */
	private $_leftJoin = array();

	/** @var string */
	private $_table = null;

	/** @var string */
	private $_type = null;

	/** @var string */
	private $_name = null;

	/** @var boolean */
	private $_get = true;

	/** @var boolean */
	private $_set = true;

	/** @var string */
	private $_aliasParentTable = null;

	/** @var array */
	private $_where = array();

	/** @var boolean */
	private $_whereSet = false;

	/** @var array */
	private $_links = array();

	/** @var string */
	private $_customOrder = null;

	/** @var callable[] */
	private $_validators = array();


	/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
	 * Public methods
	 */
	
	/**
	 * Get / set parent table alias.
	 * 
	 * When working with a self referencing table (i.e. a column in the table contains
	 * a primary key value from its own table) it can be useful to set an alias on the
	 * parent table's name, allowing a self referencing Join. For example:
	 *   ```
	 *   SELECT p2.publisher 
	 *   FROM   publisher as p2
	 *   JOIN   publisher on (publisher.idPublisher = p2.idPublisher)
	 *   ```
	 * Where, in this case, `publisher` is the table that is used by the Editor instance,
	 * and you want to use `Join` to link back to the table (resolving a name for example).
	 * This method allows that alias to be set. Fields can then use standard SQL notation
	 * to select a field, for example `p2.publisher` or `publisher.publisher`.
	 *  @param string $_ Table alias to use
	 *  @return string|self Table alias set (which is null by default), or self if used as
	 *    a setter.
	 */
	public function aliasParentTable ( $_=null )
	{
		return $this->_getSet( $this->_aliasParentTable, $_ );
	}


	/**
	 * Get / set field instances.
	 * 
	 * The list of fields designates which columns in the table that will be read
	 * from the joined table.
	 *  @param Field $_... Instances of the {@see Field} class, given as a single 
	 *    instance of {@see Field}, an array of {@see Field} instances, or multiple
	 *    {@see Field} instance parameters for the function.
	 *  @return Field[]|self Array of fields, or self if used as a setter.
	 *  @see {@see Field} for field documentation.
	 */
	public function field ( $_=null )
	{
		$args = func_get_args();

		if ( $_ !== null && !is_array($_) ) {
			$_ = $args;
		}
		return $this->_getSet( $this->_fields, $_, true );
	}


	/**
	 * Get / set field instances.
	 * 
	 * An alias of {@see field}, for convenience.
	 *  @param Field $_... Instances of the {@see Field} class, given as a single 
	 *    instance of {@see Field}, an array of {@see Field} instances, or multiple
	 *    {@see Field} instance parameters for the function.
	 *  @return Field[]|self Array of fields, or self if used as a setter.
	 *  @see {@see Field} for field documentation.
	 */
	public function fields ( $_=null )
	{
		$args = func_get_args();

		if ( $_ !== null && !is_array($_) ) {
			$_ = $args;
		}
		return $this->_getSet( $this->_fields, $_, true );
	}


	/**
	 * Get / set get attribute.
	 * 
	 * When set to false no read operations will occur on the join tables.
	 *  @param boolean $_ Value
	 *  @return boolean|self Name
	 */
	public function get ( $_=null )
	{
		return $this->_getSet( $this->_get, $_ );
	}


	/**
	 * Get / set join properties.
	 *
	 * Define how the SQL will be performed, on what columns. There are
	 * basically two types of join that are supported by Editor here, a direct
	 * foreign key reference in the join table to the parent table's primary
	 * key, or a link table that contains just primary keys for the parent and
	 * child tables (this approach is usually used with a {@see Join->type()} of
	 * 'array' since you can often have multiple links between the two tables,
	 * while a direct foreign key reference will typically use a type of
	 * 'object' (i.e. a single entry).
	 *
	 *  @param string|string[] $parent Parent table's primary key names. If used
	 *    with a link table (i.e. third parameter to this method is given, then
	 *    an array should be used, with the first element being the pkey's name
	 *    in the parent table, and the second element being the key's name in
	 *    the link table.
	 *  @param string|string[] $child Child table's primary key names. If used
	 *    with a link table (i.e. third parameter to this method is given, then
	 *    an array should be used, with the first element being the pkey's name
	 *    in the child table, and the second element being the key's name in the
	 *    link table.
	 *  @param string $table Join table name, if using a link table
	 *  @returns Join This for chaining
	 *  @deprecated 1.5 Please use the {@see Join->link()} method rather than this
	 *      method now.
	 */
	public function join ( $parent=null, $child=null, $table=null )
	{
		if ( $parent === null && $child === null ) {
			return $this->_join;
		}

		$this->_join['parent'] = $parent;
		$this->_join['child'] = $child;
		$this->_join['table'] = $table;
		return $this;
	}


	/**
	 * Set up a left join operation for the Mjoined data
	 *
	 * @param string $table to get the information from
	 * @param string $field1 the first field to get the information from
	 * @param string $operator the operation to perform on the two fields
	 * @param string $field2 the second field to get the information from
	 * @return self
	 */
	public function leftJoin ( $table, $field1, $operator, $field2 )
	{
		$this->_leftJoin[] = array(
			"table"    => $table,
			"field1"   => $field1,
			"field2"   => $field2,
			"operator" => $operator
		);

		return $this;
	}


	/**
	 * Create a join link between two tables. The order of the fields does not
	 * matter, but each field must contain the table name as well as the field
	 * name.
	 * 
	 * This method can be called a maximum of two times for an Mjoin instance:
	 * 
	 * * First time, creates a link between the Editor host table and a join
	 *   table
	 * * Second time creates the links required for a link table.
	 * 
	 * Please refer to the Editor Mjoin documentation for further details:
	 * https://editor.datatables.net/manual/php
     *
	 * @param  string $field1 Table and field name
	 * @param  string $field2 Table and field name
	 * @return Join Self for chaining
	 * @throws \Exception Link limitations
	 */
	public function link ( $field1, $field2 )
	{
		if ( strpos($field1, '.') === false || strpos($field2, '.') === false ) {
			throw new \Exception("Link fields must contain both the table name and the column name");
		}

		if ( count( $this->_links ) >= 4 ) {
			throw new \Exception("Link method cannot be called more than twice for a single instance");
		}

		$this->_links[] = $field1;
		$this->_links[] = $field2;

		return $this;
	}


	/**
	 * Specify the property that the data will be sorted by.
     *
	 * @param  string $order SQL column name to order the data by
	 * @return Join Self for chaining
	 */
	public function order ( $_=null )
	{
		// How this works is by setting the SQL order by clause, and since the
		// join that is done in PHP is always done sequentially, the order is
		// retained.
		return $this->_getSet( $this->_customOrder, $_ );
	}


	/**
	 * Get / set name.
	 * 
	 * The `name` of the Join is the JSON property key that is used when 
	 * 'getting' the data, and the HTTP property key (in a JSON style) when
	 * 'setting' data. Typically the name of the db table will be used here,
	 * but this method allows that to be overridden.
	 *  @param string $_ Field name
	 *  @return String|self Name
	 */
	public function name ( $_=null )
	{
		return $this->_getSet( $this->_name, $_ );
	}


	/**
	 * Get / set set attribute.
	 * 
	 * When set to false no write operations will occur on the join tables.
	 * This can be useful when you want to display information which is joined,
	 * but want to only perform write operations on the parent table.
	 *  @param boolean $_ Value
	 *  @return boolean|self Name
	 */
	public function set ( $_=null )
	{
		return $this->_getSet( $this->_set, $_ );
	}


	/**
	 * Get / set join table name.
	 *
	 * Please note that this will also set the {@see Join->name()} used by the Join
	 * as well. This is for convenience as the JSON output / HTTP input will
	 * typically use the same name as the database name. If you want to set a
	 * custom name, the {@see Join->name()} method must be called ***after*** this one.
	 *  @param string $_ Name of the table to read the join data from
	 *  @return String|self Name of the join table, or self if used as a setter.
	 */
	public function table ( $_=null )
	{
		if ( $_ !== null ) {
			$this->_name = $_;
		}
		return $this->_getSet( $this->_table, $_ );
	}


	/**
	 * Get / set the join type.
	 * 
	 * The join type allows the data that is returned from the join to be given
	 * as an array (i.e. working with multiple possibly results for each record from
	 * the parent table), or as an object (i.e. working which one and only one result
	 * for each record form the parent table).
	 *  @param string $_ Join type ('object') or an array of 
	 *    results ('array') for the join.
	 *  @return String|self Join type, or self if used as a setter.
	 */
	public function type ( $_=null )
	{
		return $this->_getSet( $this->_type, $_ );
	}


	/**
	 * Set a validator for the array of data (not on a field basis)
	 *
	 * @param string $fieldName Name of the field that any error should be shown
	 *   against on the client-side
	 * @param callable $fn Callback function for validation
	 * @return self Chainable
	 */
	public function validator ( $fieldName, $fn )
	{
		$this->_validators[] = array(
			'fieldName' => $fieldName,
			'fn' => $fn
		);

		return $this;
	}


	/**
	 * Where condition to add to the query used to get data from the database.
	 * Note that this is applied to the child table.
	 * 
	 * Can be used in two different ways:
	 * 
	 * * Simple case: `where( field, value, operator )`
	 * * Complex: `where( fn )`
	 *
	 *  @param string|callable $key   Single field name or a closure function
	 *  @param string|string[] $value Single field value, or an array of values.
	 *  @param string          $op    Condition operator: <, >, = etc
	 *  @return string[]|self Where condition array, or self if used as a setter.
	 */
	public function where ( $key=null, $value=null, $op='=' )
	{
		if ( $key === null ) {
			return $this->_where;
		}

		if ( is_callable($key) && is_object($key) ) {
			$this->_where[] = $key;
		}
		else {
			$this->_where[] = array(
				"key"   => $key,
				"value" => $value,
				"op"    => $op
			);
		}

		return $this;
	}


	/**
	 * Get / set if the WHERE conditions should be included in the create and
	 * edit actions.
	 * 
	 * This means that the fields which have been used as part of the 'get'
	 * WHERE condition (using the `where()` method) will be set as the values
	 * given.
	 *
	 * This is default false (i.e. they are not included).
	 *
	 *  @param boolean $_ Include (`true`), or not (`false`)
	 *  @return boolean Current value
	 */
	public function whereSet ( $_=null )
	{
		return $this->_getSet( $this->_whereSet, $_ );
	}



	/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
	 * Internal methods
	 */

	/**
	 * Get data
	 *  @param Editor $editor Host Editor instance
	 *  @param string[] $data Data from the parent table's get and were we need
	 *    to add out output.
	 *  @param array $options options array for fields
	 *  @internal
	 */
	public function data( $editor, &$data, &$options )
	{
		if ( ! $this->_get ) {
			return;
		}

		$this->_prep( $editor );
		$db       = $editor->db();
		$dteTable = $editor->table();
		$pkey     = $editor->pkey();
		$idPrefix = $editor->idPrefix();

		$dteTable = $dteTable[0];
		if ( strpos($dteTable, ' as ') !== false ) {
			$arr = explode(' as ', $dteTable);
			$dteTable = $arr[0];
			$this->_aliasParentTable = $arr[1];
		}
		
		$dteTableLocal = $this->_aliasParentTable ? // Can be aliased to allow a self join
			$this->_aliasParentTable :
			$dteTable;
		$joinField = isset($this->_join['table']) ?
			$this->_join['parent'][0] :
			$this->_join['parent'];

		// This is something that will likely come in a future version, but it
		// is a relatively low use feature. Please get in touch if this is
		// something you require.
		if ( count( $pkey ) > 1 ) {
			throw new \Exception("MJoin is not currently supported with a compound primary key for the main table", 1);
		}

		if ( count($data) > 0 ) {
			$pkey = $pkey[0];
			$pkeyIsJoin = $pkey === $joinField || $pkey === $dteTableLocal.'.'.$joinField;

			// Set up the JOIN query
			$stmt = $db
				->query( 'select' )
				->distinct( true )
				->get( $dteTableLocal.'.'.$joinField.' as dteditor_pkey' )
				->get( $this->_fields('get') )
				->table( $dteTable .' as '. $dteTableLocal );

			if ( $this->order() ) {
				$stmt->order( $this->order() );
			}

			$stmt->left_join($this->_leftJoin);
			$this->_apply_where( $stmt );

			if ( isset($this->_join['table']) ) {
				// Working with a link table
				$stmt
					->join(
						$this->_join['table'],
						$dteTableLocal.'.'.$this->_join['parent'][0] .' = '. $this->_join['table'].'.'.$this->_join['parent'][1]
					)
					->join(
						$this->_table,
						$this->_table.'.'.$this->_join['child'][0] .' = '. $this->_join['table'].'.'.$this->_join['child'][1]
					);
			}
			else {
				// No link table in the middle
				$stmt
					->join(
						$this->_table,
						$this->_table.'.'.$this->_join['child'] .' = '. $dteTableLocal.'.'.$this->_join['parent']
					);
			}

			// Check that the joining field is available.  The joining key can
			// come from the Editor instance's primary key, or any other field,
			// including a nested value (from a left join). If the instance's 
			// pkey, then we've got that in the DT_RowId parameter, so we can
			// use that. Otherwise, the key must be in the field list.
			if ( $this->_propExists( $dteTable.'.'.$joinField, $data[0] ) ) {
				$readField = $dteTable.'.'.$joinField;
			}
			else if ( $this->_propExists( $joinField, $data[0] ) ) {
				$readField = $joinField;
			}
			else if ( ! $pkeyIsJoin ) {
				echo json_encode( array(
					"sError" => "Join was performed on the field '{$joinField}' which was not "
						."included in the Editor field list. The join field must be included "
						."as a regular field in the Editor instance."
				) );
				exit(0);
			}

			// Get list of pkey values and apply as a WHERE IN condition
			// This is primarily useful in server-side processing mode and when filtering
			// the table as it means only a sub-set will be selected
			// This is only applied for "sensible" data sets. It will just complicate
			// matters for really large data sets:
			// https://stackoverflow.com/questions/21178390/in-clause-limitation-in-sql-server
			if ( count($data) < 1000 ) {
				$whereIn = array();

				for ( $i=0 ; $i<count($data) ; $i++ ) {
					$whereIn[] = $pkeyIsJoin ? 
						str_replace( $idPrefix, '', $data[$i]['DT_RowId'] ) :
						$this->_readProp( $readField, $data[$i] );
				}

				$stmt->where_in( $dteTableLocal.'.'.$joinField, $whereIn );
			}

			// Go!
			$res = $stmt->exec();
			if ( ! $res ) {
				return;
			}

			// Map to primary key for fast lookup
			$join = array();
			while ( $row=$res->fetch() ) {
				$inner = array();

				for ( $j=0 ; $j<count($this->_fields) ; $j++ ) {
					$field = $this->_fields[$j];
					if ( $field->apply('get') ) {
						$field->write($inner, $row);
					}
				}

				if ( $this->_type === 'object' ) {
					$join[ $row['dteditor_pkey'] ] = $inner;
				}
				else {
					if ( !isset( $join[ $row['dteditor_pkey'] ] ) ) {
						$join[ $row['dteditor_pkey'] ] = array();
					}
					$join[ $row['dteditor_pkey'] ][] = $inner;
				}
			}

			// Loop over the data and do a join based on the data available
			for ( $i=0 ; $i<count($data) ; $i++ ) {
				$rowPKey = $pkeyIsJoin ? 
					str_replace( $idPrefix, '', $data[$i]['DT_RowId'] ) :
					$this->_readProp( $readField, $data[$i] );

				if ( isset( $join[$rowPKey] ) ) {
					$data[$i][ $this->_name ] = $join[$rowPKey];
				}
				else {
					$data[$i][ $this->_name ] = ($this->_type === 'object') ?
						(object)array() : array();
				}
			}
		}

		// Field options
		foreach ($this->_fields as $field) {
			$opts = $field->optionsExec( $db );

			if ( $opts !== false ) {
				$name = $this->name().
					($this->_type === 'object' ? '.' : '[].').
					$field->name();
				$options[ $name ] = $opts;
			}
		}
	}


	/**
	 * Create a row.
	 *  @param Editor $editor Host Editor instance
	 *  @param int $parentId Parent row's primary key value
	 *  @param string[] $data Data to be set for the join
	 *  @internal
	 */
	public function create ( $editor, $parentId, $data )
	{
		// If not settable, or the many count for the join was not submitted
		// there we do nothing
		if (
			! $this->_set ||
			! isset($data[$this->_name]) || 
			! isset($data[$this->_name.'-many-count'])
		) {
			return;
		}

		$this->_prep( $editor );
		$db = $editor->db();
		
		if ( $this->_type === 'object' ) {
			$this->_insert( $db, $parentId, $data[$this->_name] );
		}
		else {
			for ( $i=0 ; $i<count($data[$this->_name]) ; $i++ ) {
				$this->_insert( $db, $parentId, $data[$this->_name][$i] );
			}
		}
	}


	/**
	 * Update a row.
	 *  @param Editor $editor Host Editor instance
	 *  @param int $parentId Parent row's primary key value
	 *  @param string[] $data Data to be set for the join
	 *  @internal
	 */
	public function update ( $editor, $parentId, $data )
	{
		// If not settable, or the many count for the join was not submitted
		// there we do nothing
		if ( ! $this->_set || ! isset($data[$this->_name.'-many-count']) ) {
			return;
		}

		$this->_prep( $editor );
		$db = $editor->db();
		
		if ( $this->_type === 'object' ) {
			// update or insert
			$this->_update_row( $db, $parentId, $data[$this->_name] );
		}
		else {
			// WARNING - this will remove rows and then readd them. Any
			// data not in the field list WILL BE LOST
			// todo - is there a better way of doing this?
			$this->remove( $editor, array($parentId) );
			$this->create( $editor, $parentId, $data );
		}
	}


	/**
	 * Delete rows
	 *  @param Editor $editor Host Editor instance
	 *  @param int[] $ids Parent row IDs to delete
	 *  @internal
	 */
	public function remove ( $editor, $ids )
	{
		if ( ! $this->_set ) {
			return;
		}

		$that = $this;
		$this->_prep( $editor );
		$db = $editor->db();
		
		if ( isset($this->_join['table']) ) {
			$stmt = $db
				->query( 'delete' )
				->table( $this->_join['table'] )
				->or_where( $this->_join['parent'][1], $ids )
				->exec();
		}
		else {
			$stmt = $db
				->query( 'delete' )
				->table( $this->_table )
				->where_group( function ( $q ) use ( $that, $ids ) {
					$q->or_where( $that->_join['child'], $ids );
				} );

			$this->_apply_where( $stmt );

			$stmt->exec();
		}
	}


	/**
	 * Validate input data
	 *
	 * @param array $errors Errors array
	 * @param Editor $editor Editor instance
	 * @param string[] $data Data to validate
	 * @param string $action `create` or `edit`
	 * @internal
	 */
	public function validate ( &$errors, $editor, $data, $action )
	{
		if ( ! $this->_set && ! isset($data[$this->_name.'-many-count']) ) {
			return;
		}

		$this->_prep( $editor );

		$joinData = isset($data[$this->_name]) ?
			$data[$this->_name] :
			array();

		for ( $i=0 ; $i<count($this->_validators) ; $i++ ) {
			$validator = $this->_validators[$i];
			$fn = $validator['fn'];
			$res = $fn( $editor, $action, $joinData );

			if ( is_string($res) ) {
				$errors[] = array(
					"name" => $validator['fieldName'],
					"status" => $res
				);
			}
		}

		if ( $this->_type === 'object' ) {
			$this->_validateFields( $errors, $editor, $joinData, $this->_name.'.' );
		}
		else {
			for ( $i=0 ; $i<count($joinData) ; $i++ ) {
				$this->_validateFields( $errors, $editor, $joinData[$i], $this->_name.'[].' );
			}
		}
	}



	/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
	 * Private methods
	 */
	
	/**
	 * Add local WHERE condition to query
	 *  @param \DataTables\Database\Query $query Query instance to apply the WHERE conditions to
	 *  @private
	 */
	private function _apply_where ( $query )
	{
		for ( $i=0 ; $i<count($this->_where) ; $i++ ) {
			if ( is_callable( $this->_where[$i] ) ) {
				$this->_where[$i]( $query );
			}
			else {
				$query->where(
					$this->_where[$i]['key'],
					$this->_where[$i]['value'],
					$this->_where[$i]['op']
				);
			}
		}
	}


	/**
	 * Create a row.
	 *  @param \DataTables\Database $db Database reference to use
	 *  @param int $parentId Parent row's primary key value
	 *  @param string[] $data Data to be set for the join
	 *  @private
	 */
	private function _insert( $db, $parentId, $data )
	{
		if ( isset($this->_join['table']) ) {
			// Insert keys into the join table
			$stmt = $db
				->query('insert')
				->table( $this->_join['table'] )
				->set( $this->_join['parent'][1], $parentId )
				->set( $this->_join['child'][1], $data[$this->_join['child'][0]] )
				->exec();
		}
		else {
			// Insert values into the target table
			$stmt = $db
				->query('insert')
				->table( $this->_table )
				->set( $this->_join['child'], $parentId );

			for ( $i=0 ; $i<count($this->_fields) ; $i++ ) {
				$field = $this->_fields[$i];

				if ( $field->apply( 'set', $data ) ) { // TODO should be create or edit
					$stmt->set( $field->dbField(), $field->val('set', $data) );
				}
			}

			// If the where condition variables should also be added to the database
			// Note that `whereSet` is now deprecated
			if ( $this->_whereSet ) {
				for ( $i=0, $ien=count($this->_where) ; $i<$ien ; $i++ ) {
					if ( ! is_callable( $this->_where[$i] ) ) {
						$stmt->set( $this->_where[$i]['key'], $this->_where[$i]['value'] );
					}
				}
			}

			$stmt->exec(); 
		}
	}


	/**
	 * Prepare the instance to be run.
	 *
	 * @param  Editor $editor Editor instance
	 * @private
	 */
	private function _prep ( $editor )
	{
		$links = $this->_links;

		// Were links used to configure this instance - if so, we need to
		// back them onto the join array
		if ( $this->_join['parent'] === null && count($links) ) {
			$editorTable = $editor->table();
			$editorTable = $editorTable[0];
			$joinTable = $this->table();
			if ( strpos($editorTable, ' as ') !== false ) {
				$arr = explode(' as ', $editorTable);
				$editorTable = $arr[0];
				$this->_aliasParentTable = $arr[1];
			}

			if ( $this->_aliasParentTable ) {
				$editorTable = $this->_aliasParentTable;
			}

			if ( count( $links ) === 2 ) {
				// No link table
				$f1 = explode( '.', $links[0] );
				$f2 = explode( '.', $links[1] );

				if ( $f1[0] === $editorTable ) {
					$this->_join['parent'] = $f1[1];
					$this->_join['child'] = $f2[1];
				}
				else {
					$this->_join['parent'] = $f2[1];
					$this->_join['child'] = $f1[1];
				}
			}
			else {
				// Link table
				$f1 = explode( '.', $links[0] );
				$f2 = explode( '.', $links[1] );
				$f3 = explode( '.', $links[2] );
				$f4 = explode( '.', $links[3] );

				// Discover the name of the link table
				if ( $f1[0] !== $editorTable && $f1[0] !== $joinTable ) {
					$this->_join['table'] = $f1[0];
				}
				else if ( $f2[0] !== $editorTable && $f2[0] !== $joinTable ) {
					$this->_join['table'] = $f2[0];
				}
				else if ( $f3[0] !== $editorTable && $f3[0] !== $joinTable ) {
					$this->_join['table'] = $f3[0];
				}
				else {
					$this->_join['table'] = $f4[0];
				}

				$this->_join['parent'] = array( $f1[1], $f2[1] );
				$this->_join['child'] = array( $f3[1], $f4[1] );
			}
		}
	}


	/**
	 * Update a row.
	 *  @param \DataTables\Database $db Database reference to use
	 *  @param int $parentId Parent row's primary key value
	 *  @param string[] $data Data to be set for the join
	 *  @private
	 */
	private function _update_row ( $db, $parentId, $data )
	{
		if ( isset($this->_join['table']) ) {
			// Got a link table, just insert the pkey references
			$db->push(
				$this->_join['table'],
				array(
					$this->_join['parent'][1] => $parentId,
					$this->_join['child'][1]  => $data[$this->_join['child'][0]]
				),
				array(
					$this->_join['parent'][1] => $parentId
				)
			);
		}
		else {
			// No link table, just a direct reference
			$set = array(
				$this->_join['child'] => $parentId
			);

			for ( $i=0 ; $i<count($this->_fields) ; $i++ ) {
				$field = $this->_fields[$i];

				if ( $field->apply( 'set', $data ) ) {
					$set[ $field->dbField() ] = $field->val('set', $data);
				}
			}

			// Add WHERE conditions
			$where = array($this->_join['child'] => $parentId);
			for ( $i=0, $ien=count($this->_where) ; $i<$ien ; $i++ ) {
				$where[ $this->_where[$i]['key'] ] = $this->_where[$i]['value'];

				// Is there any point in this? Is there any harm?
				// Note that `whereSet` is now deprecated
				if ( $this->_whereSet ) {
					if ( ! is_callable( $this->_where[$i] ) ) {
						$set[ $this->_where[$i]['key'] ] = $this->_where[$i]['value'];
					}
				}
			}

			$db->push( $this->_table, $set, $where );
		}
	}


	/**
	 * Create an SQL string from the fields that this instance knows about for
	 * using in queries
	 *  @param string $direction Direction: 'get' or 'set'.
	 *  @returns array Fields to include
	 *  @private
	 */
	private function _fields ( $direction )
	{
		$fields = array();

		for ( $i=0 ; $i<count($this->_fields) ; $i++ ) {
			$field = $this->_fields[$i];

			if ( $field->apply( $direction, null ) ) {
				if ( strpos( $field->dbField() , "." ) === false ) {
					$fields[] = $this->_table.'.'.$field->dbField() ." as ".$field->dbField();;
				}
				else {
					$fields[] = $field->dbField();// ." as ".$field->dbField();
				}
			}
		}

		return $fields;
	}


	/**
	 * Validate input data
	 *
	 * @param array $errors Errors array
	 * @param Editor $editor Editor instance
	 * @param string[] $data Data to validate
	 * @param string $prefix Field error prefix for client-side to show the
	 *   error message on the appropriate field
	 * @internal
	 */
	private function _validateFields ( &$errors, $editor, $data, $prefix )
	{
		for ( $i=0 ; $i<count($this->_fields) ; $i++ ) {
			$field = $this->_fields[$i];
			$validation = $field->validate( $data, $editor );

			if ( $validation !== true ) {
				$errors[] = array(
					"name" => $prefix.$field->name(),
					"status" => $validation
				);
			}
		}
	}
}
