feat: add support for the $lookup step in $aggregate

index.js

@@ -71,11 +71,24 @@ function extendMemoryDB(MemoryDB) {
   };
 
   ShareDBMingo.prototype._querySync = function(snapshots, query, _options) {
+    var db = this;
     if (Array.isArray(query.$aggregate)) {
       // sharedb-mongo passes the $aggregate pipeline straight to Mongo, so
       // convert Snapshot instances to Mongo doc format for Mingo to operate on.
       var mongoDocs = snapshots.map(castToMongoDoc);
-      var mingoAgg = new Mingo.Aggregator(query.$aggregate);
+      var aggregatorOptions = {
+        // support $lookup
+        collectionResolver: function(collection) {
+          var collectionDocs = db.docs[collection];
+          var collectionSnapshots = [];
+          for (var id in collectionDocs || {}) {
+            var snapshot = db._getSnapshotSync(collection, id, true);
+            collectionSnapshots.push(snapshot);
+          }
+          return collectionSnapshots.map(castToMongoDoc);
+        }
+      };
+      var mingoAgg = new Mingo.Aggregator(query.$aggregate, aggregatorOptions);
       var aggResult = mingoAgg.run(mongoDocs);
       return {snapshots: [], extra: aggResult};
     }
@@ -121,7 +134,8 @@ function extendMemoryDB(MemoryDB) {
         query.hasOwnProperty('$sort') ||
         query.hasOwnProperty('$limit') ||
         query.hasOwnProperty('$skip') ||
-        query.hasOwnProperty('$count')
+        query.hasOwnProperty('$count') ||
+        query.hasOwnProperty('$aggregate')
     );
   };
 

test/query.js

@@ -162,6 +162,62 @@ module.exports = function() {
         });
       });
     });
+
+    it('supports $lookup', function(done) {
+      var users = [
+        {type: 'json0', id: 'user1', v: 1, data: {name: 'Alice', age: 30}},
+        {type: 'json0', id: 'user2', v: 1, data: {name: 'Bob', age: 25}}
+      ];
+      var orders = [
+        {type: 'json0', id: 'order1', v: 1, data: {userId: 'user1', item: 'Book'}},
+        {type: 'json0', id: 'order2', v: 1, data: {userId: 'user2', item: 'Pen'}},
+        {type: 'json0', id: 'order3', v: 1, data: {userId: 'user1', item: 'Notebook'}}
+      ];
+      var query = {
+        $aggregate: [
+          {$lookup: {
+            from: 'users',
+            localField: 'userId',
+            foreignField: '_id',
+            as: 'userDetails'
+          }},
+          {$unwind: '$userDetails'},
+          {$project: {
+            _id: 1,
+            item: 1,
+            userName: '$userDetails.name',
+            userAge: '$userDetails.age'
+          }},
+          {$sort: {userName: 1, item: 1}}
+        ]
+      };
+
+      var db = this.db;
+      async.series([
+        function(cb) {
+          async.each(users, function(user, innerCb) {
+            db.commit('users', user.id, {v: 0, create: {}}, user, null, innerCb);
+          }, cb);
+        },
+        function(cb) {
+          async.each(orders, function(order, innerCb) {
+            db.commit('orders', order.id, {v: 0, create: {}}, order, null, innerCb);
+          }, cb);
+        },
+        function(cb) {
+          db.query('orders', query, null, null, function(err, results, extra) {
+            if (err) return cb(err);
+            expect(results).eql([]);
+            expect(extra).eql([
+              {_id: 'order1', item: 'Book', userName: 'Alice', userAge: 30},
+              {_id: 'order3', item: 'Notebook', userName: 'Alice', userAge: 30},
+              {_id: 'order2', item: 'Pen', userName: 'Bob', userAge: 25}
+            ]);
+            cb();
+          });
+        }
+      ], done);
+    });
   });
 
   describe('filtering on special Share properties', function() {