Difficult to delete a specific relationship

[maxdemarzi]

Difficult to delete a specific relationship

[pboling]

👍 I also need to know this.

[maxdemarzi]

Not sure what you are asking here actually. You can delete a relationship like so:

new_node1 = @neo.create_node
new_node2 = @neo.create_node
new_relationship = @neo.create_relationship("friends", new_node1, new_node2, {"since" => '10-1-2010', "met" => "college"})
@neo.delete_relationship(new_relationship)

new_relationship["end"]  points to the new_node2

You mean to delete all relationships of that node?

START max=node:node_auto_index(name="Max")
MATCH (max)-[r?]->()
DELETE r;

That would do it.

I guess we could add a delete relationships method to do this?

Is that what you are asking or something else?

[camertron]

Thanks for your response @maxdemarzi. In your example, you build the relationship and then delete it right away. In my case, I don't have a reference to the relationship yet. I need to be able to get a reference to that exact relationship, then pass it to delete_relationship. Here's the workaround we came up with:

relationship_ids = @neo.execute_script("g.v(#{parent_node.neo_id}).outE('#{relationship_name}').inV.filter { ... }.back(2).id")
relationship_ids.each { |rel_id| @neo.delete_relationship(rel_id) }

It would be great if Neography could encapsulate finding relationship ids as above.

[pboling]

This is my problem as well. I never want to create and then immediately delete a relationship. I create it, lose the reference, and then eons later need to delete it.

[maxdemarzi]

Ah ok.

node1_rels = @neo.get_node_relationships(1)
node1_rels.each { |rel_id| @neo.delete_relationship(rel_id) }

You can also get a specific type or direction for the relationships see:

    def get_node_relationships(id, dir = nil, types = nil)
      @node_relationships.get(id, dir, types)
    end

This is in https://github.com/maxdemarzi/neography/blob/master/lib/neography/rest.rb#L166

[pboling]

Awesome, thanks @maxdemarzi !

[camertron]

Right, that's pretty much exactly what I pointed to in my original post. The problem with using get_node_relationships, even with the direction and types options, is the number of potential matches returned. I want to get the specific relationship between node1 and node2 - I don't care about any of the other relationships between node1 and other nodes. Here's what I'm envisioning:

rels = @neo.get_node_relationships(node1, node2)  # there may be more than one, eg. multiple types
node1_rels.each { |rel_id| @neo.delete_relationship(rel_id) }

Is it really a problem to just be able to specify two nodes and get back the relationship(s) between them? I mean, create_relationship(node1, node2) creates a relationship between node1 and node2 - why isn't there a complementary function that takes the same arguments to get/delete the same relationship? I admit, I'm pretty new to the graph database world, maybe I'm just misunderstanding the fundamentals.

[maxdemarzi]

It would be nice if the REST API did that...

GET http://localhost:7474/db/data/node/362/relationships/363 <-- get em all.
GET http://localhost:7474/db/data/node/362/relationships/363/in <-- get all Incoming.
GET http://localhost:7474/db/data/node/362/relationships/363/all/LIKES&HATES   <-- for example would get both incoming and outgoing likes & hates rels between these two nodes (if any exist).

Maybe we can add it to Neo4j... or we can cheat and fake it with cypher.

[maxdemarzi]

Am I losing it or can't we just do this with the traversal part of the REST API?

[maxdemarzi]

Ok... so I added the ability to just get the relationships between two nodes.

See fd13a05

These should all be possible now. Try it, and let me know if you find something not working.

rels = @neo.get_node_relationships_to(node1, node2) 
rels = @neo.get_node_relationships_to(node1, node2, "in") 
rels = @neo.get_node_relationships_to(node1, node2, "in", "enemies") 
rels = @neo.get_node_relationships_to(node1, node2, "in", ["friends", "enemies"]) 
rels.each { |rel_id| @neo.delete_relationship(rel_id) }

[pboling]

Awesome! Thanks @maxdemarzi , I will test this out soon.

[camertron]

Cool, thanks @maxdemarzi!