Updating an embedded document in MongoDB with official C# driver

.net, c#, mongodb, mongodb-.net-driver

Solution

You could use the positional array modification feature of MongoDB to update an entire division in the array at once as follows:

var division = GetDivisionById(1);
division.Name = "New Name";
// change any other properties of division you want
collection.Update(
    Query.EQ("Divisions._id", 1),
    Update.Set("Divisions.$", BsonDocumentWrapper.Create<IDivision>(division))
);

The key things going on here are:

- The use of the "$" in Update.Set

- Since Update.Set requires a BsonValue as its second argument we have to use a BsonDocumentWrapper to hold the division value (the IDivision type parameter to Create sets the nominalType at serialization to IDivision which results in the "_t" discriminator being written).

Problem

If I have a Company collection which contains embedded Divisions: ``` { "_id": 1 "_t": "Company", "Name": "Test Company" "Divisions": [ { "_id": 1 "_t": "Division", "Name": "Test Division 1" }, { "_id": 2 "_t": "Division", "Name": "Test Division 2" } ] } ``` What is the best way to save/update an entire Division when using the official 10gen C# driver? (The latest 0.9 release.) I'm using Update.AddToSetWrapped to add Divisions, and that works fine, but I'd also like to be able to update documents depending on their _id. For example, if I define the following Update method: ``` public void UpdateDivision(IDivision division) { var mongo = MongoServer.Create(_connectionString); var database = mongo.GetDatabase(_databaseName); var query = Query.EQ("_id", division.CompanyId); var update = Update.AddToSetWrapped("Divisions", division); database.GetCollection<Company>("Company") .Update(query, update, UpdateFlags.Upsert, SafeMode.True); } ``` and call it like so: ``` var division = GetDivisionById(1); division.Name = "New Name"; UpdateDivision(division); ``` Then a new instance of Division will be added to the set, because although the "_id" is still 1, the Name is different, and therefore it is a unique document. So what is there a good way to update a whole embedded document? Until I come up with a better solution I am going to first `$pull` the original Division and then `$addToSet` with the modified Division. That works but is obviously not ideal as it performs two separate updates.

Original source