Updating Value of Array Element in MongoDB

Question

I'd like to know how to update the "value" field of one of the elements identified by the "name" field in the array "array_of_stuff". For example, I want to update the value for "name_of_thing_1" to "new_value_of_thing_1". How can I do this ONLY using the second parameter (i.e. the update parameter) to the update command. I am re-using a class library written in-house I don't have control over the first argument to the update command (i.e. the query parameter). Is this possible?

{
"array_of_stuff": [
 {
 "name": "name_of_thing_1",
 "value": "value_of_thing_1", 
 },
 {
 "name": "name_of_thing_2",
 "value": "value_of_thing_2",
 }
]
}

Thanks for your help!

Answer 1

You can update the value of a single item in an array (if you know its index) like this:

db.stuff.update(/* query ... */, {$set:{"arrayname.<index>":new_value}})

If your array contains documents, you can update a particular field of a document at that index like this:

db.stuff.update(/* query ... */, {$set:{"array_of_stuff.0.value":"new_value_of_thing_1"}})
// If you could use the query parameter and knew something
// about the value in the array you wanted to change:
db.stuff.update({"array_of_stuff.value":"value_of_thing_1"}, {$set:{"array_of_stuff.$.value":"new_value_of_thing_1"}})

Answer 2

See if this example help you:

db.bruno.insert({"array": [{"name": "Hello", "value": "World"}, {"name": "Joker", "value": "Batman"}]})
db.bruno.update({"array.name": "Hello"}, {$set: {"array.$.value": "Change"}})
db.bruno.find().pretty()

output:

db.bruno.find().pretty()
{
 "_id" : ObjectId("52389faaafd72821e7b25a73"),
 "array" : [
 {
 "name" : "Hello",
 "value" : "Change"
 },
 {
 "name" : "Joker",
 "value" : "Batman"
 }
 ]
}

Answer 3

I don't think it is possible. In order to update field of one of the elements in array, you should use positional $ operator, e.g.:

update({'array_of_stuff.name':'name_of_thing_1'}, 
 { $set: {'array_of_stuff.$.value':'new_value_of_thing_1'}})

But according to documentation: positional $ operator acts as a placeholder for the first element that matches query document, and the array field must appear as part of the query document.