ArangoDB AQL: Update single object in embedded array

Question

I am trying to update the attribute on a json document in an embedded array using AQL. How do i update the "addressline" for "home" type address using AQL below?

User:

{
name: "test",
address: [
      {"addressline": "1234 superway", type:"home"}, 
      {"addressline": "5678 superway", type:"work"}
     ]
}

AQL Attempt so far

for u in users
   for a in u.address
     FILTER a.type='home'
       UPDATE u WITH {<What goes here to update addressline?>} in users

Thank you for the help.

Regards, Anjan

Answer 1

To do this we have to work with temporary variables. We will collect the sublist in there and alter it. We choose a simple boolean filter condition to make the query better comprehensible.

First lets create a collection with a sample:

database = db._create('complexCollection')
database.save({ 
  "topLevelAttribute" : "a", 
  "subList" : [ 
    { 
      "attributeToAlter" : "oldValue", 
      "filterByMe" : true 
    }, 
    { 
      "attributeToAlter" : "moreOldValues", 
      "filterByMe" : true 
    }, 
    { 
      "attributeToAlter" : "unchangedValue", 
      "filterByMe" : false 
    } 
  ] 
})

Heres the Query which keeps the subList on alteredList to update it later:

FOR document in complexCollection
  LET alteredList = (
    FOR element IN document.subList 
       LET newItem = (! element.filterByMe ?
                      element :
                      MERGE(element, { attributeToAlter: "shiny New Value" }))
       RETURN newItem)
  UPDATE document WITH { subList:  alteredList } IN complexCollection

While the query as it is is now functional:

db.complexCollection.toArray()
[ 
  { 
    "_id" : "complexCollection/392671569467", 
    "_key" : "392671569467", 
    "_rev" : "392799430203", 
    "topLevelAttribute" : "a", 
    "subList" : [ 
      { 
        "filterByMe" : true, 
        "attributeToAlter" : "shiny New Value" 
      }, 
      { 
        "filterByMe" : true, 
        "attributeToAlter" : "shiny New Value" 
      }, 
      { 
        "filterByMe" : false, 
        "attributeToAlter" : "unchangedValue" 
      } 
    ] 
  } 
]

This query will probably be soonish a performance bottleneck, since it modifies all documents in the collection regardless whether the values change or not . Therefore we want to only UPDATE the documents if we really change their value. Therefore we employ a second FOR to test whether subList will be altered or not:

FOR document in complexCollection
  LET willUpdateDocument = (
    FOR element IN document.subList 
      FILTER element.filterByMe LIMIT 1 RETURN 1)

  FILTER LENGTH(willUpdateDocument) > 0

  LET alteredList = (
    FOR element IN document.subList 
       LET newItem = (! element.filterByMe ?
                      element :
                      MERGE(element, { attributeToAlter: "shiny New Value" }))
       RETURN newItem)

  UPDATE document WITH { subList:  alteredList } IN complexCollection

Answer 2

ArangoDB now supports subset indexes. The following query is based on dothebart s answer:

FOR document IN complexCollection
    FILTER document.subList[*].filterByMe == true LIMIT 1
    UPDATE document WITH {
        items: (
            FOR element IN document.subList
                RETURN element.filterByMe == true
                     ? MERGE(element, { attributeToAlter: "the shiniest value"})
                     : element
        )
    } IN complexCollection

Note : Don't forget to create a hash index on subList[*].filterByMe :

db._collection('complexCollection')
    .ensureIndex({type:'hash',fields:['subList[*].filterByMe']});