$unwind

Unwinding arrays and document arrays expands them into individual documents so that aggregation can take place of the resulting output. For example, mapping the roles array of an account with 3 roles results in 3 output documents, each containing a roles ObjectId property.

{"$unwind": <property>}

Example

GET /accounts/?pipeline=[{"$project": {"roles": 1}}, {"$unwind": "roles"}]

{
    "data": [
        {
            "_id": "55ff9db67a00a89c14aa31a6",
            "object": "account",
            "roles": "000000000000000000000004"
        },
        {
            "_id": "55ff9db67a00a89c14aa31a6",
            "object": "account",
            "roles": "000000000000000000000005"
        },
        {
            "_id": "55ff9db67a00a89c14aa31a6",
            "object": "account",
            "roles": "000000000000000000000007"
        }
    ],
    "hasMore": false,
    "object": "list"
}