Wrap delete operations in subqueries

[mathix420]

Description

Wrap delete operations in subqueries.

Issue

#440 (comment)

Checklist

The following requirements should have been met (depending on the changes in the branch):

• Documentation has been updated
• TCK tests have been updated
• Integration tests have been updated
• Example applications have been updated
• New files have copyright header
• CLA (https://neo4j.com/developer/cla/) has been signed

[darrellwarde]

Currently blocked by a potential Cypher bug - a dialogue has been opened with the Cypher team.

[darrellwarde]

Sadly we're not going to be able to get the Cypher bug fix for this ported back to 4.1/4.2, so we're going to have to use an alternative approach until 4.3 becomes our minimum supported version!

To get the information in the right place, we have been guided an example of the fix here with subqueries:

MATCH (this:Movie)
WHERE this.id = $this_id

WITH this
OPTIONAL MATCH (this)<-[this_actors0_delete0_relationship:ACTED_IN]-(this_actors0_delete0:Actor)
WHERE this_actors0_delete0.name = $updateMovies.args.update.actors[0].delete[0].where.node.name

WITH this, this_actors0_delete0
OPTIONAL MATCH (this_actors0_delete0)-[this_actors0_delete0_movies0_relationship:ACTED_IN]->(this_actors0_delete0_movies0:Movie)
WHERE this_actors0_delete0_movies0.id = $updateMovies.args.update.actors[0].delete[0].delete.movies[0].where.node.id

WITH this, this_actors0_delete0, this_actors0_delete0_movies0
CALL {
    WITH this_actors0_delete0_movies0
    FOREACH(_ IN CASE this_actors0_delete0_movies0 WHEN NULL THEN [] ELSE [1] END |
        DETACH DELETE this_actors0_delete0_movies0
    )
    RETURN count(*)
}

WITH this, this_actors0_delete0
CALL {
    WITH this_actors0_delete0
    FOREACH(_ IN CASE this_actors0_delete0 WHEN NULL THEN [] ELSE [1] END |
        DETACH DELETE this_actors0_delete0
    )
    RETURN count(*)
}

RETURN this { .id, actors: [ (this)<-[:ACTED_IN]-(this_actors:Actor)   | this_actors { .name } ] } AS this

Could have an alternative solution something along the lines of:

MATCH (this:Movie)
WHERE this.id = $this_id

WITH this
MATCH (this)<-[this_actors0_delete0_relationship:ACTED_IN]-(this_actors0_delete0:Actor)
WHERE this_actors0_delete0.name = $name

WITH this, this_actors0_delete0
MATCH (this_actors0_delete0)-[this_actors0_delete0_movies0_relationship:ACTED_IN]->(this_actors0_delete0_movies0:Movie)
WHERE this_actors0_delete0_movies0.id = $id

WITH this, this_actors0_delete0, this_actors0_delete0_movies0

WITH this, collect(DISTINCT this_actors0_delete0) AS actorsToDelete, collect(DISTINCT this_actors0_delete0_movies0) AS moviesToDelete 
FOREACH (x in moviesToDelete | DETACH DELETE x)
FOREACH (x in actorsToDelete | DETACH DELETE x)

RETURN this { .id, actors: [ (this)<-[:ACTED_IN]-(this_actors:Actor)   | this_actors { .name } ] } AS this

@mathix420, if you'd like to continue with this work then please feel free to experiment in this space and see if a solution similar to the above still gets the tests you've written here passing. Otherwise, we'll likely continue where this PR left off as one of our next bug fixes. Cheers!

[darrellwarde]

Superseded by #537, thanks for the work here @mathix420!