title: Node.js Mongodb graphql
body: <p>I have started a project that in using node.js and express and it's connected to a mongodb, this database has three collections (Participants, Houses, and activities), one participant can have one house and any activities! I have already done the query in graphql for each one, but I don't know how I can do the query and retrieve the relations between them. For example how I can know with participants are on a determined house... </p>