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Consider this simple setup:

class Person
  include Neo4j::ActiveNode

  property :name, type: String

  has_many :out, :follows, model_class: Person, rel_class: Friendship
  has_many :in, :followed_by, model_class: Person, rel_class: Friendship
end

class Friendship
  include Neo4j::ActiveRel

  property :key, type: String

  type 'friendship'
  from_class Person
  to_class Person
end

How would I search through all Friendships for those matching a condition? (e.g. Friendships of a certain key).

In an email, Brian Underwood points me to this snippet:

ModelClass.association_name(:node_var, :rel_var).where("rel_var = 'some_condition'")

I've tried playing around with it, but don't understand. Is ModelClass an ActiveNode or ActiveRel instance? What is :node_var and :rel_var?

David Chouinard
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1 Answers1

2

If you want to search for every friendship that has a specific key property, you'd do that like this:

Person.all.follows.rel_where(key: your_key_var)
# OR
Person.all.follows(:f, :r).where('r.key = {key}').params(key: your_key_var)

These will both generate MATCH (p:Person)-[r:friends]->(f:Person), more or less, with the first example using auto-defined node identifiers and the second using f for the destination Friend node and r for the relationship, as given by the :f, :r arguments. After that, a to_a will return the friend at the END of the chain or you can call pluck with either :f or :r to return the given objects.

The model_class option always describes the NODE class on the other side of the association. In Brian's example, node_var and rel_var are generic names for the identifiers Cypher will use in the statement that it creates.

subvertallchris
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