Filtering on multi-relationship existence

[nmonterroso]

I'm trying to create a filter that says "where a list of relationships is non-empty". For example, loading a database with:

create(n1:Person {name:"foo"}),
    (n2:Person {name:"bar"}),
    (n3:Pet {name:"baz"}),
    (n1)-[:knows]->(n2),
    (n2)-[:knows]->(n3)

with the schema:

type Person {
	name: String!
	friends: [Person!]! @relation(name:"knows",direction:OUT)
	pets: [Pet!] @relation(name:"knows",direction:OUT)
}

type Pet {
	name: String!
}

I want a query that says "find me only the people that know a Person, regardless of whether or not they know any Pets". Based on the filter documentation I was hoping to use something like:

{
  person (filter: { friends_not: null }) {
    name
    friends {
      name
    }
    pets {
      name
    }
  }
}

but this produces the following error: Input for friends must be an filter-InputType. I also tried a few different queries:

• (filter: { friends: { name_not: null } }) - I was hoping this would work indirectly since it would match into the friend node and filter on the name, but that produced this cypher:
  • MATCH (person:Person) WHERE ALL(person_Person_Cond IN [(person)-[:knows]->(person_Person) | (NOT person_Person.name = $filterPerson_PersonName)] WHERE person_Person_Cond) RETURN person { .name,friends:[(person)-[:knows]->(personFriends:Person) | personFriends { .name }],pets:[(person)-[:knows]->(personPets:Pet) | personPets { .name }] } AS person
  • the NOT person_Person.name = $filterPerson_PersonName since $filterPerson_PersonName is null the query does not get the expected results, and when I manually change it to an is null, I also get the unexpected result of both Persons.
• (filter: { friends_not: [] }) - Input for friends must be an filter-InputType

I created nmonterroso/neo4j-graphql-java-filters to illustrate this issue.

Any help is greatly appreciated!

EDIT - This also affects the server plugin neo4j-graphql, and I've created neo4j-graphql#177 for that side of the equation.

[jexp]

Great question,

usually, it would be something like: friends_none: { name: "Joe" }

But I think we don't have an operator yet that check existence.
So it would be great to add.

I wonder if an empty friends_some: {} would work, but I think graphql doesn't allow empty input types.

[nmonterroso]

I added another test to my repo with (filter: { friends_some: {} }), and I'm getting the following cypher:

MATCH (person:Person) WHERE  ANY(person_Person_Cond IN [(person)-[:knows]->(person_Person) | ] WHERE person_Person_Cond) RETURN person { .name,friends:[(person)-[:knows]->(personFriends:Person) | personFriends { .name }],pets:[(person)-[:knows]->(personPets:Pet) | personPets { .name }] } AS person

which throws the following error:

Neo.ClientError.Statement.SyntaxError: Invalid input ']': expected whitespace, comment or an expression (line 1, column 94 (offset: 93))
"MATCH (person:Person) WHERE  ANY(person_Person_Cond IN [(person)-[:knows]->(person_Person) | ] WHERE person_Person_Cond) RETURN person { .name,friends:[(person)-[:knows]->(personFriends:Person) | personFriends { .name }],pets:[(person)-[:knows]->(personPets:Pet) | personPets { .name }] } AS person"

[johnymontana]

FYI - this use case is covered in neo4j-graphql.js

See an example in the tests

and some example use cases in this issue

[jexp]

Thanks @johnymontana

[rgruener]

I am needing this feature for an internal project. I might have some time to help out implementing it though obviously I am not familiar with the project at all so if I could be pointed in the right direction for fixing this maybe I can take a crack at it.

[Andy2003]

@nmonterroso / @rgruener Can you please take a look at PR #179. I would say that the requested queries can currently be handled with the current master version.