Enable filtering one-many related objects by number of related objects

[islamaliev]

At the moment it is possible to filter secondary objects by certain criteria in primary objects. Like so:

query {
    Author(filter: {published: {rating: {_gt: 4.8}}, age: {_gt: 63}}) {
        name
    }
}

But it is not possible to find secondary objects that have no related objects:

query {
    Author(filter: {published: {_eq: null}) {
        name
    }
}

Would be also great to be able to request objects by number of related objects

query {
    Author(filter: {published: {_len: 2}) {
        name
    }
}

But for this a new _len operator needs to be implemented.

Here is a full integration test:

var bookAuthorGQLSchema = (`
    type Book {
        name: String
        rating: Float
        author: Author
    }

    type Author {
        name: String
        age: Int
        verified: Boolean
        published: [Book]
    }
`)

func TestQueryOneToMany_IfFilteredByEmptyRelations_ShouldFind(t *testing.T) {
    test := testUtils.TestCase{
        Actions: []any{
            testUtils.SchemaUpdate{
                Schema: bookAuthorGQLSchema,
            },
            testUtils.CreateDoc{
                CollectionID: 0,
                Doc: `{
                    "name": "Painted House",
                    "rating": 4.9,
                    "author_id": "bae-e1ea288f-09fa-55fa-b0b5-0ac8941ea35b"
                }`,
            },
            testUtils.CreateDoc{
                CollectionID: 0,
                Doc: `{
                    "name": "A Time for Mercy",
                    "rating": 4.5,
                    "author_id": "bae-e1ea288f-09fa-55fa-b0b5-0ac8941ea35b"
                    }`,
            },
            testUtils.CreateDoc{
                CollectionID: 0,
                Doc: `{
                    "name": "Theif Lord",
                    "rating": 4.8,
                    "author_id": "bae-72e8c691-9f20-55e7-9228-8af1cf54cace"
                }`,
            },
            testUtils.CreateDoc{
                CollectionID: 1,
                // bae-e1ea288f-09fa-55fa-b0b5-0ac8941ea35b
                Doc: `{
                    "name": "John Grisham",
                    "age": 65,
                    "verified": true
                }`,
            },
            testUtils.CreateDoc{
                CollectionID: 1,
                // bae-72e8c691-9f20-55e7-9228-8af1cf54cace
                Doc: `{
                    "name": "Cornelia Funke",
                    "age": 62,
                    "verified": false
                }`,
            },
            testUtils.CreateDoc{
                CollectionID: 1,
                // bae-6bf29c1c-7112-5f4f-bfae-1c039479acf6
                Doc: `{
                    "name": "John Tolkien",
                    "age": 70,
                    "verified": true
                }`,
            },
            testUtils.Request{
                Request: `query {
                    Author(filter: {published: {_eq: null}) {
                        name
                    }
                }`,
                Results: []map[string]any{{
                    "name": "John Tolkien",
                }},
            },
            // would be nice to have this as well
            //testUtils.Request{
            //  Request: `query {
            //      Author(filter: {published: {_len: 2}) {
            //          name
            //      }
            //  }`,
            //  Results: []map[string]any{{
            //      "name": "John Grisham",
            //  }},
            //},
        },
    }
    testUtils.ExecuteTestCase(t, test)
}

[AndrewSisley]

Note: Author(filter: {published: {_len: 2}) { is just filtering by aggregate (_count), and so is already solved by views, long term this would be handled by alias targeting for those who don't want to bother creating views.

In a one-many this also applies to Author(filter: {published: {_eq: null}), which is just another way of wording Author(filter: {published: {_len: 0}) {

I suggest we close this ticket.