when delete document in another collection How to delete edge collection document together?

Question

I am practicing arangodb in company. When I want to express the following relation between the user and the user, I want to delete the data of the corresponding following relation when one user is deleted.

user collection

{
    "_key": "test4",
    "_id": "users/test4",
    "_rev": "_V8yGRra---"
  },
  {
    "_key": "test2",
    "_id": "users/test2",
    "_rev": "_V8whISG---"
  },
  {
    "_key": "test1",
    "_id": "users/test1",
    "_rev": "_V8whFQa---"
  },
  {
    "_key": "test3",
    "_id": "users/test3",
    "_rev": "_V8yoFWO---",
    "userKey": "test3"
  }

follow collection[edge]

{
    "_key": "48754",
    "_id": "follow/48754",
    "_from": "users/test1",
    "_to": "users/test2",
    "_rev": "_V8wh4Xe---"
  }
  {
    "_key": "57447",
    "_id": "follow/57447",
    "_from": "users/test2",
    "_to": "users/test3",
    "_rev": "_V8yHGQq---"
  }

Please add code or effort which you have tried so for? – Oomph Fortuity Nov 27 '17 at 06:53 — Oomph Fortuity, Nov 27 '17 at 06:53

peak · Answer 1 · 2017-12-01T04:24:33.980

1

If used properly, the ArangoDB system ensures the integrity of named graphs (GRAPHs).

To delete a specific user (say "users/test4") and the corresponding edges in follow manually, an AQL query along the following lines should suffice to delete the edges:

for v,e IN 1..1 ANY "users/test4" follow
  REMOVE e IN follow
  COLLECT WITH COUNT INTO counter
  RETURN counter

Assuming "users/test4" is not referenced elsewhere, the node can then safely be deleted, e.g. by

 REMOVE "test4" in users

The important point here is that when manually deleting nodes, all the relevant edge collections must be identified and managed explicitly.

edited Dec 01 '17 at 04:24

answered Nov 27 '17 at 19:01

peak

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To add a bit of rewording to the last part: if you use a NAMED GRAPH explicitly, Arango will make sure that the appropriate edges get deleted. – Virmundi Dec 01 '17 at 03:23

score 0 · Answer 2 · answered Nov 27 '17 at 14:38

First you should create a graph with your vertex and edge collection. Working with graphs you can use the REST API to remove a vertex. This way all edges pointing to this vertex and the vertex itself get removed.

DELETE /_api/gharial/{graph-name}/vertex/{collection-name}/{vertex-key}

You can find the documentation including an example under https://docs.arangodb.com/3.2/HTTP/Gharial/Vertices.html#remove-a-vertex.

It is also possible to achieve this with an AQL query, for example deleting test1 from the users collection:

LET keys = (
  FOR v, e IN 1..1 ANY 'users/test1' GRAPH 'your-graph-name' RETURN e._key)
    LET r = (FOR key IN keys REMOVE key IN follow) REMOVE 'test1' IN users

A graph traversal is used to get _key attributes of all edges pointing to test1, then these edges are removed from the follow collection and test1 is removed from the users collection.

ArongoDB purports to ensure the integrity of every GRAPH, whichever interface is used. So for a GRAPH, the required AQL is trivial. It's only for non-GRAPH graphs that the explicit removal of edges is required. — peak, Nov 27 '17 at 18:45

when delete document in another collection How to delete edge collection document together?

2 Answers2