如何在 ArangoDB 中找到名为 x 的所有后代属性的总和？

Question

As i have tree structure in my graph database ArangoDB like below

The node with id 2699394 is a parent node of this graph tree. and each node has attribute named X assigned to it. I want to know sum of x of all the descendants of parent node 2699394 exclusive of its own attribute x in sum. for example suppose if,

 2699399 x value is = 5,
 2699408 x value is = 3,
 2699428 x value is = 2,
 2699418 x value is = 5,

then parent node 2699394 sum of x should be = 5 + 3 + 2 + 5 
                                            = 15

so the answer is 15. So can anybody give me query for this calculation in ArangoDB AQL?

To find out no of descendants of particular node, i have used below query,

`FOR v, e, p   in 1..1000 OUTBOUND 'Person/1648954' 
GRAPH 'Appes'
RETURN v.id`

Thanks in Advance. Mayank

Answer 1

Assuming that children are linked to their parents, the data could be visualized like this:

nodes/2699394 SUM of children?
      ↑
nodes/2699399 {x: 5}
      ↑
nodes/2699408 {x: 3}
      ↑
nodes/2699428 {x: 2}
      ↑
nodes/2699418 {x: 5}

To walk the chain of children, we need to traverse in INBOUND direction (or OUTOBUND if parent nodes point to children):

FOR v IN 1..10 INBOUND "nodes/2699394" relations
  RETURN v

In this example, an anonymous graph is used by specifying an edge collection relations . You can also use a named graph, like GRAPH "yourGraph" .

Starting at nodes/2699394 , the edges down to nodes/2699418 are traversed and every node on the way is returned unchanged so far.

Since we are only interested in the x attribute, we can change that to only return that attribute: RETURN vx - which will return [ 5, 3, 2, 5 ] . Unless we say IN 0..10 , the start vertex will not be included.

Inside the FOR loop, we don't have access to all the x values, but only one at a time. We can't do something like RETURN SUM(vx) here. Instead, we need to assign the result of the traversal to a variable, which makes it a sub-query. We can then add up all the numbers and return the resulting value:

LET x = (
  FOR v IN 1..10 INBOUND "nodes/2699394" relations
    RETURN v.x
)
RETURN SUM(x) // [ 15 ]

If you want to return the start node with a computed x attribute, you may do the following:

LET doc = DOCUMENT("nodes/2699394")
LET x = (
  FOR v IN 1..10 INBOUND doc relations
    RETURN v.x
)
RETURN MERGE( doc, { x: SUM(x) } )

The result will be like:

[
  {
    "_id": "nodes/2699394",
    "_key": "2699394",
    "_rev": "2699394",
    "x": 15
  }
]