MongoDB Many-to-Many Association

Question

How would you do a many-to-many association with MongoDB?

For example; let's say you have a Users table and a Roles table. Users have many roles, and roles have many users. In SQL land you would create a UserRoles table.

Users:
    Id
    Name

Roles:
    Id
    Name

UserRoles:
    UserId
    RoleId

How is same sort of relationship handled in MongoDB?

Answer 1

Depending on your query needs you can put everything in the user document:

{name:"Joe"
,roles:["Admin","User","Engineer"]
}

To get all the Engineers, use:

db.things.find( { roles : "Engineer" } );

If you want to maintain the roles in separate documents then you can include the document's _id in the roles array instead of the name:

{name:"Joe"
,roles:["4b5783300334000000000aa9","5783300334000000000aa943","6c6793300334001000000006"]
}

and set up the roles like:

{_id:"6c6793300334001000000006"
,rolename:"Engineer"
}