MongoDB – Query Array Property of Objects

Yesterday, I was having difficulty creating a MongoDB query for a group membership collection where I wanted to filter groups where the user belongs and having a specific role. Below is the similar data structure.

[
  {
    name: "Group name 1",
    members: [
      { id: "1001", roles: ["Owner"] },
      { id: "1002", roles: ["Member", "Editor"] },
      { id: "1003", roles: ["Member"] },
    ]
  },
  {
    name: "Group name 2",
    members: [
      { id: "1004", roles: ["Owner"] },
    ]
  },
  {
    name: "Group name 3",
    members: [
      { id: "1003", roles: ["Owner"] },
      { id: "1004", roles: ["Member"] },
    ]
  },
]

Let’s say I’m a user with ID 1003 and I wanted to filter groups where I belong to but only if I have the Owner role.

First Try

I tried this query filter first:

{
  "members.id": "1003",
  "members.roles": "Owner",
}

I’m expecting to get the Group name 3 result but I also got the Group name 1 as part of the result. It seems that it matches at least one members property to create a match instead of matching both. It makes sense because this property is an array object.

Solution

Today, I finally found the proper filter based on this guide:

https://docs.mongodb.com/manual/reference/operator/query/elemMatch/#mongodb-query-op.-elemMatch

Here is my new filter:

{
  members: {
    $elemMatch: {
      id: "1003",
      roles: "Owner"
    }
  }
}

The query will match the array property if both of the properties in the array of objects matches the specified filter. Looks good so far!

That’s it!