Can I use the Mongo Aggregation Framework via the ObjCMongoDB library?

Question

I am using the ObjCMongoDB library to back a simple iPad application. I understand the basic CRUD operations as well as use of -[MongoConnection runCommandWithDictionary:onDatabaseName:error:] to execute database commands such as findAndModify.

With respect to the Aggregation Framework or just aggregation in general, it looks like I can execute simple database commands like count in the following manner:

NSDictionary *commandDict = @{@"count": @"myCollection"}:
[myMongoConnection runCommandWithDictionary:commandDict onDatabaseName:@"myDB" error:&err];

Is it possible to execute more complex commands/queries like the examples here? I tried the following to no avail.

NSDictionary *commandDict = @{@"aggregate":@"myCollection", @"query": @{@"group":@"myDocType"}};

Am still learning both Obj-C as well as MongoDB so apologies if this is an uninformed question.

Answer 1

Your syntax for the aggregate command appears to be incorrect.

See this example from the docs for aggregate:

db.runCommand(
{ aggregate : "article", pipeline : [
  { $project : {
     author : 1,
     tags : 1,
  } },
  { $unwind : "$tags" },
  { $group : {
     _id : "$tags",
     authors : { $addToSet : "$author" }
  } }
 ] }
);

If you run the Mongo shell from the command line, you can test your command directly right there, before writing it in Objective-C.