Functional tests for $first and $last.

1 files changed, 110 insertions, 0 deletions

diff --git a/jstests/aggregation/bugs/firstlast.js b/jstests/aggregation/bugs/firstlast.js
new file mode 100644
index 00000000000..f0398aaa74f
--- /dev/null
+++ b/jstests/aggregation/bugs/firstlast.js
@@ -0,0 +1,110 @@
+// Check $first/$last group accumulators.  SERVER-3862
+// $first/$last select first/last value for a group key from the previous pipeline.
+
+t = db.jstests_aggregation_firstlast;
+t.drop();
+
+/** Check expected $first and $last result values. */
+function assertFirstLast( expectedFirst, expectedLast, pipeline, expression ) {
+    pipeline = pipeline || [];
+    expression = expression || '$b'
+    pipeline.push( { $group:{ _id:'$a',
+                              first:{ $first:expression },
+                              last:{ $last:expression } } } );
+    result = t.aggregate( pipeline ).result;
+    for( var i = 0; i < result.length; ++i ) {
+        if ( result[ i ]._id == 1 ) {
+            // Check results for group _id 1.
+            assert.eq( expectedFirst, result[ i ].first );
+            assert.eq( expectedLast, result[ i ].last );
+            return;
+        }
+    }
+    assert( false, "Expected group _id '1' missing." );
+}
+
+// One document.
+t.save( { a:1, b:1 } );
+assertFirstLast( 1, 1 );
+
+// Two documents.
+t.save( { a:1, b:2 } );
+assertFirstLast( 1, 2 );
+
+// Three documents.
+t.save( { a:1, b:3 } );
+assertFirstLast( 1, 3 );
+
+// Another 'a' key value does not affect outcome.
+t.drop();
+t.save( { a:3, b:0 } );
+t.save( { a:1, b:1 } );
+t.save( { a:1, b:2 } );
+t.save( { a:1, b:3 } );
+t.save( { a:2, b:0 } );
+assertFirstLast( 1, 3 );
+
+// Additional pipeline stages do not affect outcome if order is maintained.
+assertFirstLast( 1, 3, [ { $project:{ x:'$a', y:'$b' } }, { $project:{ a:'$x', b:'$y' } } ] );
+
+// Additional pipeline stages affect outcome if order is modified.
+assertFirstLast( 3, 1, [ { $sort:{ b:-1 } } ] );
+
+// Skip and limit affect the results seen.
+t.drop();
+t.save( { a:1, b:1 } );
+t.save( { a:1, b:2 } );
+t.save( { a:1, b:3 } );
+assertFirstLast( 1, 2, [ { $limit:2 } ] );
+assertFirstLast( 2, 3, [ { $skip:1 }, { $limit:2 } ] );
+assertFirstLast( 2, 2, [ { $skip:1 }, { $limit:1 } ] );
+
+// Mixed type values.
+t.save( { a:1, b:'foo' } );
+assertFirstLast( 1, 'foo' );
+
+t.drop();
+t.save( { a:1, b:'bar' } );
+t.save( { a:1, b:true } );
+assertFirstLast( 'bar', true );
+
+// Value null.
+t.drop();
+t.save( { a:1, b:null } );
+t.save( { a:1, b:2 } );
+assertFirstLast( null, 2 );
+t.drop();
+t.save( { a:1, b:2 } );
+t.save( { a:1, b:null } );
+assertFirstLast( 2, null );
+t.drop();
+t.save( { a:1, b:null } );
+t.save( { a:1, b:null } );
+assertFirstLast( null, null );
+
+// Value missing.
+t.drop();
+t.save( { a:1 } );
+t.save( { a:1, b:2 } );
+assertFirstLast( undefined, 2 );
+t.drop();
+t.save( { a:1, b:2 } );
+t.save( { a:1 } );
+assertFirstLast( 2, undefined );
+t.drop();
+t.save( { a:1 } );
+t.save( { a:1 } );
+assertFirstLast( undefined, undefined );
+
+// Dotted field.
+t.drop();
+t.save( { a:1, b:[ { c:1 }, { c:2 } ] } );
+t.save( { a:1, b:[ { c:6 }, {} ] } );
+assertFirstLast( [ 1, 2 ], [ 6, null ], [], '$b.c' );
+
+// Computed expressions.
+t.drop();
+t.save( { a:1, b:1 } );
+t.save( { a:1, b:2 } );
+assertFirstLast( 1, 0, [], { $mod:[ '$b', 2 ] } );
+assertFirstLast( 0, 1, [], { $mod:[ { $add:[ '$b', 1 ] }, 2 ] } );