Document the new from usage

diff --git a/lib/DBIx/Class/ResultSet.pm b/lib/DBIx/Class/ResultSet.pm
index ed08ef1..17d05f5 100644 (file)
--- a/lib/DBIx/Class/ResultSet.pm
+++ b/lib/DBIx/Class/ResultSet.pm
@@ -2798,6 +2798,58 @@ with a father in the person table, we could explicitly use C<INNER JOIN>:
     # SELECT child.* FROM person child
     # INNER JOIN person father ON child.father_id = father.id
 
+If you need to express really complex joins or you need a subselect, you
+can supply literal SQL to C<from> via a scalar reference. In this case
+the contents of the scalar will replace the table name asscoiated with the
+resultsource.
+
+WARNING: This technique might very well not work as expected on chained
+searches - you have been warned.
+
+    # Assuming the Event resultsource is defined as:
+
+        MySchema::Event->add_columns (
+            sequence => {
+                data_type => 'INT',
+                is_auto_increment => 1,
+            },
+            location => {
+                data_type => 'INT',
+            },
+            type => {
+                data_type => 'INT',
+            },
+        );
+        MySchema::Event->set_primary_key ('sequence');
+
+    # This will get back the latest event for every location. The column
+    # selector is still provided by DBIC, all we do is add a JOIN/WHERE
+    # combo to limit the resultset
+
+    $rs = $schema->resultset('Event');
+    $table = $rs->result_source->name;
+    $latest = $rs->search (
+        undef,
+        { from => \ " 
+            (SELECT e1.* FROM $table e1 
+                JOIN $table e2 
+                    ON e1.location = e2.location 
+                    AND e1.sequence < e2.sequence 
+                WHERE e2.sequence is NULL 
+            ) me",
+        },
+    );
+
+    # Equivalent SQL (with the DBIC chunks added):
+
+    SELECT me.sequence, me.location, me.type FROM
+       (SELECT e1.* FROM events e1
+           JOIN events e2
+               ON e1.location = e2.location
+               AND e1.sequence < e2.sequence
+           WHERE e2.sequence is NULL
+       ) me;
+
 =head2 for
 
 =over 4