Connecting to multiple nodes produces too many results

[darrellwarde]

Describe the bug
When connecting using a where clause which produces more than one node to connect to, the update Mutation returns an array entry for each node connected to, when it should only return the root node.

The data itself is in the correct shape, just the return value is off.

Type definitions

type Movie {
  title: String!
  owners: [User!]! @relationship(type: "OWNS", direction: IN)
}

type User {
  name: String!
  movies: [Movie!]! @relationship(type: "OWNS", direction: OUT)
}

To Reproduce
Steps to reproduce the behavior:

1. With an empty database, create some test data:

mutation {
  createUsers(input: [{ name: "darrell" }]) {
    users {
      name
    }
  }
}

mutation {
  createMovies(
    input: [
      { title: "Batman Begins" }
      { title: "The Dark Knight" }
      { title: "The Dark Knight Rises" }
    ]
  ) {
    movies {
      title
    }
  }
}

2. Execute the following Mutation:

mutation {
  updateUsers(
    where: { name: "darrell" }
    connect: { movies: [{ where: { title_CONTAINS: "The Dark Knight" } }] }
  ) {
    users {
      name
      movies {
        title
      }
    }
  }
}

3. You will see the following incorrect result:

{
  "data": {
    "updateUsers": {
      "users": [
        {
          "name": "darrell",
          "movies": [
            {
              "title": "The Dark Knight"
            }
          ]
        },
        {
          "name": "darrell",
          "movies": [
            {
              "title": "The Dark Knight"
            },
            {
              "title": "The Dark Knight Rises"
            }
          ]
        }
      ]
    }
  }
}

Expected behavior
The result to be:

{
  "data": {
    "updateUsers": {
      "users": [
        {
          "name": "darrell",
          "movies": [
            {
              "title": "The Dark Knight"
            },
            {
              "title": "The Dark Knight Rises"
            }
          ]
        }
      ]
    }
  }
}

System (please complete the following information):

• OS: macOS
• Version: @neo4j/[email protected]
• Node.js version: 14.16.0

[darrellwarde]

Initial investigation finds that the current Cypher is:

MATCH (this:User)
WHERE this.name = $this_name
WITH this
OPTIONAL MATCH (this_connect_movies0:Movie)
WHERE this_connect_movies0.title CONTAINS $this_connect_movies0_title_CONTAINS
FOREACH(_ IN CASE this_connect_movies0 WHEN NULL THEN [] ELSE [1] END | 
MERGE (this)-[:OWNS]->(this_connect_movies0)
)
RETURN this { .name, movies: [ (this)-[:OWNS]->(this_movies:Movie)   | this_movies { .title } ] } AS this

@danstarns has suggested that refactoring to the following could fix this issue:

MATCH (this:User)
WHERE this.name = $this_name
CALL {
    WITH this
    OPTIONAL MATCH (this_connect_movies0:Movie)
    WHERE this_connect_movies0.title CONTAINS $this_connect_movies0_title_CONTAINS
    FOREACH(_ IN CASE this_connect_movies0 WHEN NULL THEN [] ELSE [1] END | 
        MERGE (this)-[:OWNS]->(this_connect_movies0)
    )
    RETURN count(*)
}
RETURN this { .name, movies: [ (this)-[:OWNS]->(this_movies:Movie)   | this_movies { .title } ] } AS this

[jadafi]

Similar as #235 ?