How To Query A Dictionary on MongoDB

Question

I have the following class

public class Group {
  [BsonId]
  public ObjectID _id {get; set;}
  [BsonElement("Me")]
  public Members Dictionary<ObjectId, UserGroupProperties> Members {get; set;}
}

How Do I query on Members property? Where Memebres.ObjectId == objectid? Thanks!

Answer 1

MongoDB has a "dot notation" for reaching into sub-objects or arrays.

Normally, the query will look something like the following:

Query.EQ("Me._id", objectid)

And will find data of this structure:

{ 
  _id: ObjectId(),
  me: [
        { _id: ObjectId(): { UserGroupProperties } },
        { _id: ObjectId(): { other UserGroupProperties } }
      ]
}

However, it looks like your data structure is a little different. Is your data like the following?

{ 
  _id: ObjectId(),
  me: {
        ObjectId(): { UserGroupProperties },
        ObjectId(): { other UserGroupProperties }
      }
}

If so, then you're looking for the existence of "me.objectid". Which is different.

The big thing to note here is that MongoDB will return the entire matched document. So if you're looking for a single UserGroupProperties your query is going to return the entire Group.