revising query to "bind" property to dataset

extensions/datasource/classes/query.php

@@ -82,7 +82,7 @@ public function __construct( connection $connection, $table );
 	 * @return $this fluent interface
 	 */
 	public function distinct( $enabled = true );
-	
+
 	/**
 	 * Joins selected dataset to include (some of) its columns.
 	 *
@@ -105,12 +105,20 @@ public function addDataset( $dataset, $condition, $parameters = null );
 	 * Adds property to fetch of all matching records in (one of the joined)
 	 * dataset(s).
 	 *
-	 * This property may be using alias. $name may contain full term. In that
+	 * This property may be using alias. `$name` may contain full term. In that
 	 * case $parameters may include some parameters replacing markers in term.
-	 *
 	 * The number of parameters must match number of markers in term.
 	 *
-	 * @param string $name property to fetch or term to evaluate on all matches
+	 * `$name` may be array consisting of explicitly selected dataset and actual
+	 * name of property to fetch from selected dataset. Dataset may be selected
+	 * by name as used on adding dataset using @see addDataset() or by index.
+	 * On using index this is either 0-based index of dataset according to order
+	 * of adding datasets **previously**. Negative index is counting in reverse
+	 * order, thus `-1` is selecting most recently added dataset whereas `0` is
+	 * selecting initial dataset of query and `1` is selecting first actually
+	 * added dataset.
+	 *
+	 * @param string[]|string $name property to fetch or term to evaluate on all matches, array of dataset name (or index in current query) and name of dataset's property
 	 * @param string $alias alias to assign for addressing fetched value in filter
 	 * @param mixed $parameters array of parameters or first of additional arguments providing one parameter each
 	 * @return $this

extensions/datasource/classes/sql_query.php

@@ -363,6 +363,12 @@ public function addDataset( $dataset, $condition, $parameters = null )
 
 	public function addProperty( $name, $alias = null, $parameters = null )
 	{
+		if ( is_array( $name ) ) {
+			$bindToDataSet = array_shift( $name );
+			$name          = array_shift( $name );
+		} else
+			$bindToDataSet = null;
+
 		if ( !is_string( $name ) || !( $name = trim( $name ) ) )
 			throw new \InvalidArgumentException( 'bad column name' );
 
@@ -371,6 +377,20 @@ public function addProperty( $name, $alias = null, $parameters = null )
 		else if ( !is_string( $alias ) || !( $alias = trim( $alias ) ) )
 			throw new \InvalidArgumentException( 'bad column alias' );
 
+
+		if ( is_integer( $bindToDataSet ) ) {
+			$sets = array_keys( $this->tables );
+			$sets = array_slice( $sets, $bindToDataSet, 1 );
+
+			if ( !count( $sets ) )
+				throw new \OutOfRangeException( 'invalid index of data set to bind property' );
+
+			$bindToDataSet = array_shift( $sets );
+		}
+
+		if ( trim( $bindToDataSet ) )
+			$name = $this->datasource()->qualifyPropertyNames( $bindToDataSet, $name );
+
 		$this->columns[$alias] = $name;
 
 		$this->collectParameters( func_get_args(), $this->columnParameters, 2 );