I have below document in MongoDB(2.4.5)
{ "_id" : 235399, "casts" : { "crew" : [ { "_id" : 1186343, "withBase" : true, "department" : "Directing", "job" : "Director", "name" : "Connie Rasinski" }, { "_id" : 86342, "withBase" : true } ] }, "likes" : 0, "rating" : 0, "rating_count" : 0, "release_date" : "1955-11-11" }
I want to remove withBase filed from array elements inside casts.crew ..
I tried this
db.coll.update({_id:235399},{$unset: { "casts.crew.withBase" : 1 } },false,true)
nothing changed.
And tried this..
db.coll.update({_id:235399},{$unset: { "casts.crew" : { $elemMatch: { "withBase": 1 } } } },false,true)
it removed entire crew array from the document.
Can someone please provide me the right query?
To remove an element, update, and use $pull in MongoDB. The $pull operator removes from an existing array all instances of a value or values that match a specified condition.
We can remove duplicate element in an array by 2 ways: using temporary array or using separate index. To remove the duplicate element from array, the array must be in sorted order. If array is not sorted, you can sort it by calling Arrays. sort(arr) method.
General idea is to use findOne https://docs.mongodb.com/manual/reference/method/db.collection.findOne/ to retrieve one random id from the duplicate records in the collection. Delete all the records in the collection other than the random-id that we retrieved from findOne option.
To remove the duplicates from an array of objects:Use the Array. filter() method to filter the array of objects. Only include objects with unique IDs in the new array.
You can use the new positional identifier
to update multiple elements in array in 3.6.
Something like
db.coll.update( {_id:235399}, {$unset: {"casts.crew.$[].withBase":""}} )
$[] removes all the withBase
property from the crews
array. It acts as a placeholder for updating all elements in array.
Use multi true to affect multiple documents.
Sorry to disappoint you, but your answer
db.coll.update({ _id:235399, "casts.crew.withBase": {$exists: true} },{ $unset: { "casts.crew.$.withBase" : true } },false,true)
is not correct. Actually it will remove the value, BUT only from the first occurrence of the subdocument, because of the way positional operator works:
the positional $ operator acts as a placeholder for the first element that matches the query document
You also can not use $unset
(as you tried before) because it can not work on arrays (and are you basically trying to remove a key from a document from the array). You also can not remove it with $pull
, because pull removes all the array, not just a field of it.
Therefore as far as I know you can not do this with a simple operator. So the last resort is doing $find
and then forEach
with save. You can see how to do this in my answer here. In your case you need to have another loop in forEach
function to iterate through array and to delete a key. I hope that you will be able to modify it. If no, I will try to help you.
P.S. If someone looks a way to do this - here is Sandra's function
db.coll.find({_id:235399}).forEach( function(doc) { var arr = doc.casts.crew; var length = arr.length; for (var i = 0; i < length; i++) { delete arr[i]["withBase"]; } db.coll.save(doc); });
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