Neo4j Cypher：如何通过条件查询获取节点

Question

I have two Neo4j Nodes and one relation:

class StayPal
  include Neo4j::ActiveNode

  has_many :in, :places, origin: :owner
  has_many :in, :shared_places, rel_class: 'HouseMate'
end

class Place
  include Neo4j::ActiveNode

  has_one :out, :owner, type: :owner_of, model_class: 'StayPal'
  has_many :out, :house_mates, rel_class: 'HouseMate'
end

class HouseMate
  include Neo4j::ActiveRel
  include Enumable

  creates_unique

  from_class 'Place'
  to_class 'StayPal'
  type 'shared_with'

  property :status, default: 0

  enum_attr status: [:pending, :approved, :declined, :cancelled]
end

Objective: My objective is get places & shared_places of staypal together but the shared places included if they are status == approved

Query:

Neo4j::Session.current.query
  .match(n: { StayPal: { user_id: 1 } })
  .match('n<-[rel1:`owner_of`]-(result_places:`Place`)')
  .match('n<-[rel2:`shared_with`]-(result_places1:`Place`)')
  .pluck(:result_places1, :result_places)

With this I am getting the places and shared places of staypal

But I want shared places where status = 1

Modified Query

Neo4j::Session.current.query
  .match(n: { StayPal: { user_id: 1 } })
  .match('n<-[rel1:`owner_of`]-(result_places:`Place`)')
  .match('n<-[rel2:`shared_with`]-result_places1:`Place`)')
  .where('result_places1.status = 1')
  .pluck(:result_places1, :result_places)

But with this I am getting no records

Some other helping queries

Neo4j::Session.current.query
  .match(n: { StayPal: { user_id: 1 } })
  .match('n<-[rel1:`owner_of`]-(result_places:`Place`)')
  .match('n<-[rel2:`shared_with`]-result_places1:`Place`)')
  .where('result_places1.status = 1')
  .pluck(:result_places1)

Output:

[CypherRelationship 1239]

Answer 1

You are using the neo4j-core Query API, which you can do and which should allow you to get ActiveNode and ActiveRel objects, but there is a higher level API which is easier:

StayPal.where(user_id: 1).places(:place1).shared_places(:places2).pluck(:place1, place2)

To do this I assumed that you add this association to Place :

has_many :both, :shared_places, type: :shared_with

Note that I used the singular form for variables. It's important to remember that when you are matching that it does one match at a time. Singular variables help us to keep that in context.

Aside from that, though, I think you have a deeper issue that your HouseMate relationship is going from a Place to a StayPal . What is your model? If you want to record two people staying in the same house, you might want to have a new node with a label like HouseMateGroup and that node could point to the Place as well as two (or more) StayPals.

EDIT:

I think I'm understanding your use case more. I would probably make the model (:StayPal)-[:LIVES_IN]->(:Place)<-[:LIVES_IN]-(:StayPal)

Any given step in that doesn't map to the idea of a "house mate", but you can easily get the housemates by following relationships/associations. So if you wanted to get housemates you might do:

pal = StayPal.find_by(user_id: 1)

pal.places.people

That would get you all of the people that are in the places which user_id: 1 is in.

If you wanted to find all places which have associated people:

Place.as(:place1).people.places(:place2).pluck(:place1, :place2)

You could even count the number of people that exist in that relationship between places:

Place.as(:place1).people(:person).places(:place2).pluck(:place1, :place2, 'count(person)')