Filtering

This page covers how to apply filters to subscriptions in the Neo4j GraphQL Library. Note, however, that:

  • Filtering can only be applied at the root of the subscription operation.

  • Aggregations are not supported on subscription types and there is currently no available method.

A subscription can be created to target the changes to a node (create/update/delete) or to a relationship (`create/`delete).

While the format slightly differs depending on whether the subscription targets a node or a relationship, providing a where argument allows for filtering on the events that are returned to the subscription.

Operators

When creating a subscription, a number of operators are available for different types in the where argument.

Equality operators

All types can be tested for either equality or non-equality. For the Boolean type, these are the only available comparison operators.

Numerical operators

The following comparison operators are available for numeric types (Int, Float, BigInt):

  • _LT

  • _LTE

  • _GTE

  • _GT

Filtering on Temporal types and Spatial types is not currently supported.

String comparison

The following case-sensitive comparison operators are only available for use on String and ID types:

  • _STARTS_WITH

  • _ENDS_WITH

  • _CONTAINS

Array comparison

The following operator is available on non-array fields, and accepts an array argument:

  • _IN

Conversely, the following operator is available on array fields, and accepts a single argument:

  • _INCLUDES

These operators are available for all types apart from Boolean.

AND/OR operators

Complex combinations of operators are possible using the AND/ OR operators. They accept as argument an array of items of the same format as the where argument.

Check Combining operators for an example.

Subscribing to node events

The where argument allows specifying filters on top-level properties of the targeted nodes. Only events matching these properties and type are returned to the subscription.

As an example, consider the following type definitions:

type Movie {
    title: String
    genre: String
    averageRating: Float
    releasedIn: Int
}

Now, here is how filtering can be applied when creating a subscription:

CREATE

To filter subscriptions to create operations for movies by their genre, here is how to do it:

subscription {
    movieCreated(where: {genre: "Drama"}) {
        createdMovie {
            title
        }
    }
}

This way, only newly created movies with the genre "Drama" trigger events to this subscription.

The where argument only filters by properties set at the moment of creation.

UPDATE

Here is how to filter subscription to update operations in movies with average rating bigger than 8:

subscription {
    movieUpdate(where: {averageRating_GT: 8}) {
        updatedMovie {
            title
        }
    }
}

This way, you should only receive events triggered by movies with the average rating bigger than 8 when they are modified.

The where argument only filters properties that already existed before the update.

This is how these events may look like:

mutation {
    makeTheMatrix: createMovies(input: {title: "The Matrix", averageRating: 8.7}) {
        title
        averageRating
    },
    makeResurrections: createMovies(input: {title: "The Matrix Resurrections", averageRating: 5.7}) {
        title
        averageRating
    },
}

mutation {
    updateTheMatrix: updateMovie(
        where: {title: "The Matrix"}
        update: {averageRating: 7.9}
    ) {
        title
    },
    updateResurrections: updateMovie(
        where: {title: "The Matrix Resurrections"}
        update: {averageRating: 8.9}
    ) {
        title
    }
}

Therefore, given the previously described subscription, these GraphQL operations should only triggered for "The Matrix" movie.

DELETE

Here is how to filter subscription to delete operations in movies by their genre, using the NOT filter:

subscription {
    movieDeleted(where: { NOT: { genre: "Comedy" } }) {
        deletedMovie {
            title
        }
    }
}

This way, only deleted movies of all genres except for "Comedy" should trigger events to this subscription.

The where argument only filters properties that already existed before the deletion process.

Combining operators

All previously mentioned operators can be combined using the AND, OR, and NOT operators. They accept an array argument with items of the same format as the where argument, which means they can also be nested to form complex combinations.

As an example, consider a user who likes comedy movies, but not romantic comedies from early 2000, and who has the Matrix Trilogy as their favorite titles. They could subscribe to any updates that cover this particular set of interests as follows:

subscription {
    movieUpdated(where: {
        OR: [
            { title_CONTAINS: "Matrix" },
            { genre: "comedy" },
            { AND: [
                { NOT: { genre: "romantic comedy" } },
                { releasedIn_GT: 2000 },
                { releasedIn_LTE: 2005 }
            ] },
        ]
    }) {
        updatedMovie {
            title
        }
    }
}

Subscribing to relationship events

When subscribing to relationship events, the where argument still allows specifying filters on the top-level properties of the targeted nodes. It also supports specifying filters on the relationship properties (edge) and on the top-level properties (node) of the nodes at the other end of the relationship. This is done by using the operators previously described, and the usage is very similar to subscribing to node events.

However, filtering by relationship events is an even more powerful logic. This is because these filters can also express the expected relationship field, or the expected concrete type at the other end of the relationship, provided that they are connected to abstract types.

Note that each relationship field specified is combined with the others using a logical OR. Only events matching these relationship field names are returned in the subscription.

You can further filter each relationship field by node and relationship properties. These fields are combined in the resulting filter with a logical AND.

As an example, in the following type definitions:

type Movie {
    title: String
    genre: String
    actors: [Actor!]! @relationship(type: "ACTED_IN", properties: "ActedIn", direction: IN)
}

type ActedIn @relationshipProperties {
    screenTime: Int!
}

type Actor {
    name: String
}

The format of the where argument is:

{
    movie: {
        # top-level properties of the node targeted for the subscription operation, supports operators
        title_IN: ["The Matrix", "Fight Club"]
    },
    createdRelationship: {
        actors: { # field name corresponding to a relationship in the type definition of the node targeted for the subscription operation
            edge: {
                 # properties of the relationship, supports operators
                screenTime_GT: 10,
            },
            node: {
                # top-level properties of the node on the other end of the relationship, supports operators
                name_STARTS_WITH: "Brad"
            }
        }
    }
}

The following sections feature examples of how filtering can be applied when creating a subscription to relationship events.

Newly created relationship

The following example filters the subscriptions to newly created relationships that are connecting a Movie from genres other than "Drama", and to an Actor with a screen time bigger than 10 minutes:

subscription {
    movieRelationshipCreated(where: { movie: { NOT: { genre: "Drama" } }, createdRelationship: { actors: { edge: { screenTime_GT: 10 } } } }) {
        movie {
            title
        }
        createdRelationship {
            actors {
                screenTime
                node {
                    name
                }
            }
        }
    }
}

The where argument only filters already existing properties at the moment of the relationship creation.

Newly deleted relationship

The following example filters the subscriptions to deleted relationships that were connecting a Movie of the genre "Comedy" or "Adventure" to an Actor named "Jim Carrey":

subscription {
    movieRelationshipDeleted(where: { movie: { genre_IN: ["Comedy", "Adventure"] }, createdRelationship: { actors: { node: { name: "Jim Carrey" } } } }) {
        movie {
            title
        }
        deletedRelationship {
            actors {
                screenTime
                node {
                    name
                }
            }
        }
    }
}

The where argument only filters properties that already existed before the relationship deletion.

Relationship-related filters

In addition to filtering node or relationship properties, the relationship-related filtering logic is even more powerful. This is because these filters can also express the expected relationship field, or the expected concrete type at the other end of the relationship, provided that they are connected to abstract types.

The following examples are valid for both CREATE_RELATIONSHIP and DELETE_RELATIONSHIP events. Their purpose is to illustrate the various ways in which a subscription to a relationship event can be filtered.

Considering the following type definitions:

type Movie {
    title: String
    genre: String
    actors: [Actor!]! @relationship(type: "ACTED_IN", properties: "ActedIn", direction: IN)
    directors: [Director!]! @relationship(type: "DIRECTED", properties: "Directed", direction: IN)
    reviewers: [Reviewer!]! @relationship(type: "REVIEWED", properties: "Review", direction: IN)
}

type ActedIn @relationshipProperties {
    screenTime: Int!
}

type Actor {
    name: String
}

type Person implements Reviewer {
    name: String
    reputation: Int
}

union Director = Person | Actor

type Directed @relationshipProperties {
    year: Int!
}

interface Reviewer {
    reputation: Int!
}

type Magazine implements Reviewer {
    title: String
    reputation: Int!
}

type Review @relationshipProperties {
    score: Int!
}

And the base subscription operation:

subscription MovieRelationshipDeleted($where: MovieRelationshipDeletedSubscriptionWhere) {
    movieRelationshipDeleted(where: $where) {
        movie {
            title
        }
        deletedRelationship {
            actors {
                screenTime
                node {
                    name
                }
            }
            directors {
                year
                node {
                    ... on PersonEventPayload { # generated type
                        name
                        reputation
                    }
                    ... on ActorEventPayload { # generated type
                        name
                    }
                }
            }
            reviewers {
                score
                node {
                    reputation
                    ... on MagazineEventPayload { # generated type
                        title
                        reputation
                    }
                    ... on PersonEventPayload { # generated type
                        name
                        reputation
                    }
                }
            }
        }
    }
}

You can use the following where inputs in the GraphQL variable values to get different results:

Filtering via implicit/explicit declaration

Implicit or explicit declaration is used to filter specific relationship types that are expected to be returned to a subscription.

For example, when subscribing to created or deleted relationships to a Movie, a user might only be interested in the relationship of type ACTED_IN, but indifferent to the properties of the Actor node or the other relationships connected to it. In this case, the corresponding field name of this relationship is actors.

By explicitly specifying the actors field name, you can filter-out events to other relationship properties:

{
    where: {
        deletedRelationship: {
            actors: {} # no properties specified here, therefore all relationships to this field name will be returned
        }
    }
}

In case you are interested in Actor nodes conforming to some filters, for example with the name starting with the letter "A", the procedure is no different than subscribing to node events:

{
    where: {
        deletedRelationship: {
            actors: {
                node: { # use operations to specify filers on the top-level properties of the node at the other end of the relationship
                    name_STARTS_WITH: "A"
                }
            }
        }
    }
}

If you are also interested in the relationship itself conforming to some filters, such as the Actor having spent no more than 40 minutes in the Movie, this is how the query may look:

{
    where: {
        deletedRelationship: {
            actors: {
                edge: { # use operations to specify filers on the top-level properties of the relationship
                    screenTime_LT: 40,
                }
                node: {
                    name: "Alvin"
                }
            }
        }
    }
}

Multiple relationship types can also be included in the returned subscriptions by explicitly specifying the corresponding field names. For instance:

{
    where: {
        deletedRelationship: {
            actors: {}, # include all relationships corresponding of type `ACTED_IN`
            directors: {} # include all relationships corresponding of type `DIRECTED`
            # exclude relationships of type `REVIEWED`
        }
    }
}

Now, if you are interested in all relationship types, you can either express this implicitly by not specifying any:

{
    where: {
        deletedRelationship: {} # include all relationships of all types
    }
}

Or explicitly by specifying the field names of all the relationships connected to the type targeted for the subscription:

{
    where: {
        deletedRelationship: {
            # include all relationships of all types
            # subscription target type is `Movie`, which has the following relationship field names:
            actors: {},
            directors: {},
            reviewers: {}
        }
    }
}

Note, however, that as any filters are applied to any of the relationships, explicitly including those that you are interested in subscribing to is a mandatory step.

For example, if all relationships should be returned, but you want to filter-out the REVIEWED ones which have a score lower than 7, this is how your query may look like:

{
    where: {
        deletedRelationship: {
            actors: {}, # include all relationships of type `ACTED_IN`
            directors: {}, # include all relationships of type `DIRECTED`
            reviewers: { # include all relationships of type `REVIEWED`, with the score property greater than 7
                edge: {
                    score_GT: 7
                }
            }
        }
    }
}

Different filters can also be applied to different relationships without any constraints. For example:

{
    where: {
        deletedRelationship: {
            actors: { # include some relationships of type `ACTED_IN`, filtered by relationship property `screenTime` and node property `name`
                edge: {
                    screenTime_LT: 60,
                },
                node: {
                    name_IN: ["Tom Hardy", "George Clooney"]
                }
            },
            directors: {}, # include all relationships of type `DIRECTED`
            reviewers: { # include some relationships of type `REVIEWED`, filtered by relationship property `score` only
                edge: {
                    score_GT: 7
                }
            }
        }
    }
}

In the previous example, there is an implicit logical OR between the actors, directors, and reviewers relationship fields. This is to say that a relationship of either type ACTED_IN or of type DIRECTED or of type REVIEWED should trigger the previously described subscription.

There is an implicit logical AND between the edge and node fields inside of the actors relationship field. In other words, the relationship of type ACTED_IN with the property screenTime less than 60 and a target node with name in ["Tom Hardy", "George Clooney"] should trigger the subscription.

Abstract types

The following sections describe how to filter subscriptions using abstract types.

Union type

This example illustrates how to filter the node at the other end of the relationship when it is of a union type:

{
    where: {
        deletedRelationship: {
            directors: { # relationship to a union type
                Person: { # concrete type that makes up the union type
                    edge: {
                        year_GT: 2010
                    },
                    node: {
                        name: "John Doe",
                        reputation: 10
                    }
                },
                Actor: { # concrete type that makes up the union type
                    edge: {
                        year_LT: 2005
                    },
                    node: {
                        name: "Tom Hardy"
                    }
                }
            },
        }
    }
}

The result is that only relationships of type DIRECTED are returned to the subscription, where the Director is a Person named "John Doe", who directed the movie after 2010, or where the Director is an Actor named "Tom Hardy" who directed the movie before 2005.

Note that the relationship field name is split into multiple sections, one for each of the concrete types that make up the union type. The relationship properties do not exist outside the confines of one of these sections, even though the properties are the same.

Now, take the other example that did not explicitly specify the concrete types:

{
    where: {
        deletedRelationship: {
            directors: {}, # include all relationships of type `DIRECTED`
        }
    }
}

Following the same logic as for the relationship field names: when nothing is explicitly provided, then all is accepted. Thus relationships of type DIRECTED, established between a Movie and any of the concrete types that make up the union type Director are returned to the subscription.

It is equivalent to the following:

{
    where: {
        deletedRelationship: {
            directors: { # include all relationships of type `DIRECTED`
                Actor: {},
                Person: {}
            }
        }
    }
}

Note that explicitly specifying a concrete type excludes the others from the returned events:

{
    where: {
        deletedRelationship: {
            directors: {
                Actor: {} # include all relationships of type `DIRECTED` to an `Actor` type
            }
        }
    }
}

In this case, only relationships of type DIRECTED between a Movie and an Actor are returned to the subscription. Those between a Movie and a Person are filtered out.

One reason why this might be done is to include some filters on the Actor type:

{
    where: {
        deletedRelationship: {
            directors: {
                Actor: { # include some relationships of type `DIRECTED` to an `Actor` type, that conform to the filters
                    node: {
                        NOT: { name: "Tom Hardy" }
                    }
                }
            }
        }
    }
}

To include filters on the Actor type, but also include the Person type in the result, you need to make the intent explicit:

{
    where: {
        deletedRelationship: {
            directors: {
                Actor: { # include some relationships of type `DIRECTED` to an `Actor` type, that conform to the filters
                    node: {
                        NOT: { name: "Tom Hardy" }
                    }
                },
                Person: {} # include all relationships of type `DIRECTED` to a `Person` type
            }
        }
    }
}

Interface type

The following example illustrates how to filter the node at the other end of the relationship when it is of an interface type:

{
    where: {
        deletedRelationship: {
            reviewers: { # relationship to an interface type
                edge: {
                    # relationship properties of a relationship of type `REVIEWED`
                    score_GT: 7
                },
                node: {
                    # common fields declared by the interface
                    reputation_GTE: 8
                }
            },
        }
    }
}

This example returns events for relationships between the type Movie and Reviewer, where the score is higher than 7, and the Reviewer has a reputation greater or equal to 7.