图形数据库-如何从关系中引用节点

Question

I'm preparing a graph database (using neo4j) to handle the kind of social network scenario:

• Users can Post to their walls, sharing the Posts with either specific users
• Users can send Messages to others
• A Message can either be a text or "link" to the Post

So I came up with the following idea:

Users and Posts are the Nodes of the graph. When the user A creates a post P sharing it with both B and C , the following relationships are created: A-[:posted]->p and p-[:shared_with]->B and p-[:shared_with]->C . The Post data (id, text, date) are stored as properties of the :posted relation.

For messages it's similar: A-[:messaged]->C for example.

Now, if I want to share the post in a message, I include the post_id in :messaged properties. It allows me to pull all the messages (together with the posts linked) with a single Cypher query:

match (a:User) match (b) where a.username = "C" match a-[m:messaged]-b 
optional match (x:User)-[p:posted]->(post:Post)
where post.id = m.post_id
return distinct
m.post_id,
  startnode(m).username as from, 
  endnode(m).username as to ,
  x.username as PostAuthor,
  case x when null then "Message" else "Pulled Post" end as Type,
  case x when null then m.text else post.text end as Text, 
  m.date
order by m.date asc

It doesn't look right to me though - since on the graph there's no visual connection between the Post and the message. But, I can't set a relation between Node and Relation, right? How should I do it in order to have it designed properly?

Answer 1

In a model where post and message are both a node, your query would look like this:

match (a:User)<-[:FROM]-(m:Message)-[:TO]->(b:User) 
where a.username = "C" 
match (m)<-[:COMMENT]-(post:Post)<-[:POSTED]-(x:User)
return distinct
  m.id,a as from, b as to,
  x.username as PostAuthor,
  case x when null then "Message" else "Pulled Post" end as Type,
  case x when null then m.text else post.text end as Text, 
  m.date
order by m.date asc