Update field in exact element array in MongoDB

Question

I have a document structured like this:

{     _id:"43434",     heroes : [         { nickname : "test",  items : ["", "", ""] },         { nickname : "test2", items : ["", "", ""] },     ] } 

Can I $set the second element of the items array of the embedded object in array heros with nickname "test" ?

Result:

{     _id:"43434",     heroes : [         { nickname : "test",  items : ["", "new_value", ""] }, // modified here         { nickname : "test2", items : ["", "", ""] },     ] } 

Answer 1

You need to make use of 2 concepts: mongodb's positional operator and simply using the numeric index for the entry you want to update.

The positional operator allows you to use a condition like this:

{"heroes.nickname": "test"} 

and then reference the found array entry like so:

{"heroes.$  // <- the dollar represents the first matching array key index 

As you want to update the 2nd array entry in "items", and array keys are 0 indexed - that's the key 1.

So:

> db.denis.insert({_id:"43434", heroes : [{ nickname : "test",  items : ["", "", ""] }, { nickname : "test2", items : ["", "", ""] }]}); > db.denis.update(     {"heroes.nickname": "test"},      {$set: {         "heroes.$.items.1": "new_value"     }} ) > db.denis.find() {     "_id" : "43434",      "heroes" : [         {"nickname" : "test", "items" : ["", "new_value", "" ]},         {"nickname" : "test2", "items" : ["", "", "" ]}     ] } 

Answer 2

Try update document in array using positional $,

The positional $ operator facilitates updates to arrays that contain embedded documents. Use the positional $ operator to access the fields in the embedded documents with the dot notation on the $ operator.

db.collection.update(   { "heroes.nickname": "test" },   { $set: { "heroes.$.items.1": "new_value" } },   { multi: true } ); 

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