如何在AQL中使用NEIGHBORS？

Question

I'm new to ArangoDB and a growing fan already. Among many things we need to translate many-to-many relations into graphs, and query efficiently in there. However I can't seem to reproduce the behaviour in NEIGHBORS as described in the cookbook under "Using Edge Collections".

After I insert data and run:

FOR b IN books RETURN { book: b, authors: NEIGHBORS(books, written, b._id, 'inbound') }
[
  {
    "book" : {
      "_id" : "books/10519631898915",
      "_key" : "10519631898915",
      "_rev" : "10519631898915",
      "title" : "The beauty of JOINS"
    },
    "authors" : [ ]
  }
]

Empty authors list! I tried this instead:

FOR b IN books RETURN { book: b, authors: NEIGHBORS(authors, written, b._id, 'inbound') }
[
  {
    "book" : {
      "_id" : "books/10519631898915",
      "_key" : "10519631898915",
      "_rev" : "10519631898915",
      "title" : "The beauty of JOINS"
    },
    "authors" : [
      "authors/10519474612515",
      "authors/10519475792163"
    ]
  }
]

Which returns the _id list. None of those return what I need as in the cookbook, which is the expected edge/vertex structure. (All has been tested in 2.6.9)

How is the use of NEIGHBORS intended and how do I get to my goal in pure AQL? Is there a standard documentation of NEIGHBORS (and other graph AQL features) somewhere with description and type of each argument as well as return value?

Answer 1

Right, I found one solution:

FOR p IN PATHS(books, written, 'inbound') 
RETURN p.destination

Result:

Warnings:

[1577], 'collection 'books' used as expression operand'

Result:

[
  {
    "_id": "books/10519631898915",
    "_rev": "10519631898915",
    "_key": "10519631898915",
    "title": "The beauty of JOINS"
  },
  {
    "_id": "authors/10519474612515",
    "_rev": "10519474612515",
    "_key": "10519474612515",
    "name": {
      "first": "John",
      "last": "Doe"
    }
  },
  {
    "_id": "authors/10519475792163",
    "_rev": "10519475792163",
    "_key": "10519475792163",
    "name": {
      "first": "Maxima",
      "last": "Musterfrau"
    }
  }
]

It gets the destination vertices at least, but it doesn't seem right since I get a warning and the source vertex is included as a destination. Further elaboration and suggestions are very welcome.

Answer 2

Have you tried the includeData option for NEIGHBORS?

FOR b IN books RETURN { book: b, authors: NEIGHBORS(authors, written, b._id, 'inbound', [], {includeData: true}) }

That worked in my test. It will be way more performant then PATHS on large datasets (PATHS computes much more irrelevant information)

Note: The empty array [] is used to define edges that should be followed only. With an empty array we follow all edges, but you could also follow special edges fe {label: "written"} instead of [] .

Answer 3

UPDATE (2017): NEIGHBORS is no longer supported in AQL 3.x

Instead of

NEIGHBORS(books, written, b._id, 'inbound')

you could write a sub-query:

(FOR v IN 1..1 INBOUND b written RETURN v)