Update with AddToSet not updating null value with MongoDB C#

Question

Using MongoDB, I'm having trouble adding en element to an Array when the array is null. AddToSet works as expected if I add the item from the console. I am using the official C# driver from 10gen.

var query = Query.EQ("_id", objectId);          
var itemDoc = item.ToBsonDocument();

//items is an array but currently null
var update = MongoDB.Driver.Builders.Update.AddToSet("items", itemDoc); // YUNoWork?

//somefield doesn't exist
var workingUpdate = MongoDB.Driver.Builders.Update.AddToSet("somefield", itemDoc); //works fine

var collection = DataBase.GetCollection<MyObject>(CollectionName);

collection.Update(query, update); // doesn't work
collection.Update(query, workingUpdate); // works

Is this expected behavior? If so, is there a more general way to add items to an array?

HatAndBeard · Accepted Answer · 2012-03-30 16:44:49Z

14

Did some digging, according to some other comments - like you say, if the element doesn't exist, it works, but if it's null - it doesn't work. Apparently this is by design.

One suggestion was to add the BsonIgnoreIfNull attribute to arrays, which will mean your AddToSet will then work.

edited Mar 30, 2012 at 16:44

HatAndBeard

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answered Mar 29, 2012 at 1:32

user111013

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2 Comments

HatAndBeard Over a year ago

Using BsonIgnoreIfNull for lists resolves the impedance mismatch between the C# class definitions and MongoDB. Thanks!

adam0101 Over a year ago

Just to clarify for anyone else who sees this answer, you'll have to clean up your existing data for this to work. In other words, if you already have a document with a null property, you'll have to delete the property or the document. Then this will work the next time you use AddToSet. I had added the attribute, but it still didn't work because the data had already been saved with the null.

Tooraj Jam · Accepted Answer · 2020-12-02 20:01:46Z

1

Instead of null value, put an empty array.

answered Dec 2, 2020 at 20:01

Tooraj Jam

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