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?

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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