Support counting distinct values with aggregate by group

Author: GromNaN

src/Query/Builder.php

@@ -315,6 +315,7 @@ public function toMql(): array
         if ($this->groups || $this->aggregate) {
             $group   = [];
             $unwinds = [];
+            $set = [];
 
             // Add grouping columns to the $group part of the aggregation pipeline.
             if ($this->groups) {
@@ -352,15 +353,22 @@ public function toMql(): array
 
                     $aggregations = blank($this->aggregate['columns']) ? [] : $this->aggregate['columns'];
 
-                    if (in_array('*', $aggregations) && $function === 'count' && empty($group['_id'])) {
+                    if ($column === '*' && $function === 'count' && ! $this->groups) {
                         $options = $this->inheritConnectionOptions($this->options);
 
                         return ['countDocuments' => [$wheres, $options]];
                     }
 
+                    // "aggregate" is the name of the field that will hold the aggregated value.
                     if ($function === 'count') {
-                        // Translate count into sum.
-                        $group['aggregate'] = ['$sum' => 1];
+                        if ($column === '*' || $aggregations === []) {
+                            // Translate count into sum.
+                            $group['aggregate'] = ['$sum' => 1];
+                        } else {
+                            // Count the number of distinct values.
+                            $group['aggregate'] = ['$addToSet' => '$' . $column];
+                            $set['aggregate'] = ['$size' => '$aggregate'];
+                        }
                     } else {
                         $group['aggregate'] = ['$' . $function => '$' . $column];
                     }
@@ -387,6 +395,10 @@ public function toMql(): array
                 $pipeline[] = ['$group' => $group];
             }
 
+            if ($set) {
+                $pipeline[] = ['$set' => $set];
+            }
+
             // Apply order and limit
             if ($this->orders) {
                 $pipeline[] = ['$sort' => $this->aliasIdForQuery($this->orders)];
@@ -627,6 +639,10 @@ public function aggregate($function = null, $columns = ['*'])
      */
     public function aggregateByGroup(string $function, array $columns = ['*'])
     {
+        if (count($columns) > 1) {
+            throw new InvalidArgumentException('Aggregating by group requires zero or one columns.');
+        }
+
         return $this->aggregate($function, $columns);
     }
 

tests/QueryBuilderTest.php

@@ -622,17 +622,25 @@ public function testSubdocumentArrayAggregate()
     public function testAggregateGroupBy()
     {
         DB::table('users')->insert([
-            ['name' => 'John Doe', 'role' => 'admin', 'score' => 1],
-            ['name' => 'Jane Doe', 'role' => 'admin', 'score' => 2],
+            ['name' => 'John Doe', 'role' => 'admin', 'score' => 1, 'active' => true],
+            ['name' => 'Jane Doe', 'role' => 'admin', 'score' => 2, 'active' => true],
             ['name' => 'Robert Roe', 'role' => 'user', 'score' => 4],
         ]);
 
         $results = DB::table('users')->groupBy('role')->orderBy('role')->aggregateByGroup('count');
         $this->assertInstanceOf(LaravelCollection::class, $results);
         $this->assertEquals([(object) ['role' => 'admin', 'aggregate' => 2], (object) ['role' => 'user', 'aggregate' => 1]], $results->toArray());
 
+        $results = DB::table('users')->groupBy('role')->orderBy('role')->aggregateByGroup('count', ['active']);
+        $this->assertInstanceOf(LaravelCollection::class, $results);
+        $this->assertEquals([(object) ['role' => 'admin', 'aggregate' => 1], (object) ['role' => 'user', 'aggregate' => 0]], $results->toArray());
+
+        $results = DB::table('users')->groupBy('role')->orderBy('role')->aggregateByGroup('max', ['score']);
+        $this->assertInstanceOf(LaravelCollection::class, $results);
+        $this->assertEquals([(object) ['role' => 'admin', 'aggregate' => 2], (object) ['role' => 'user', 'aggregate' => 4]], $results->toArray());
+
         if (! method_exists(Builder::class, 'countByGroup')) {
-            $this->markTestSkipped('countBy* function require Laravel v11.38+');
+            $this->markTestSkipped('*byGroup functions require Laravel v11.38+');
         }
 
         $results = DB::table('users')->groupBy('role')->orderBy('role')->countByGroup();
@@ -656,6 +664,14 @@ public function testAggregateGroupBy()
         $this->assertEquals([(object) ['role' => 'admin', 'aggregate' => 1.5], (object) ['role' => 'user', 'aggregate' => 4]], $results->toArray());
     }
 
+    public function testAggregateByGroupException(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Aggregating by group requires zero or one columns.');
+
+        DB::table('users')->aggregateByGroup('max', ['foo', 'bar']);
+    }
+
     public function testUpdateWithUpsert()
     {
         DB::table('items')->where('name', 'knife')