在子文档数组中插入新字段

Question

I have the following schema:

{
   "name"    : "MyName",
   "actions" : [{
       "kind"   : "kind1",
       "result" : "result1"
   },
   {
       "kind":"kind1",
       "result":"result1"
   }
   ]
}

I want to insert a new field called 'expected' in different subdocument in actions. I tried the following command but I have an issue with it:

db.tasks.update({},{$push:{ "actions.expected" : "MyExpected" }},false,true)
can't append to array using string field name expected

Answer 1

You can use the $addToSet functionality:

http://docs.mongodb.org/manual/reference/operator/update/addToSet/

Try

db.tasks.update({}, {$addToSet: {'actions.expected': 'MyExpected'}})

Answer 2

You have json object inside array but in the query you are trying to add string. Thats why you got an exception. You can update your query as follows.

db.tasks.update({},{$push:{ "actions" : {"expected" : "MyExpected"} }},false,true)

Answer 3

Well, the problem is that you're trying to $push into an array, but the destination you're giving is not an array.

actions.expected is the expected field in the actions field, and you're pushing "MyExpected" into that array - but such an array does not exist.

Let's assume you had the following data, perhaps that explains it best. Your query would work on a data structure like this:

actions : { expected : [] } // actions is an object here
// ... {$push:{ "actions.expected" : "MyExpected" }}
actions : { expected : ["MyExpected"] }

Instead, you'll probably want to push an object into the actions array:

actions : []
$push : { "actions" : { "expected" : "MyExpected" } }
actions : [ { "expected" : "MyExpected" } ]