Update without retrieving

you can update a single or batch of entities on the mongodb server by supplying a filter criteria and a subset of properties and the data/ values to be set on them as shown below.

await DB.Update<Author>()
        .Match(a => a.Surname == "Stark")
        .Modify(a => a.Name, "Brandon")
        .Modify(a => a.Surname, "The Broken")
        .ExecuteAsync();

specify the filter criteria with a lambda expression using the .Match() method to indicate which entities/documents you want to target for the update. then use multiples of the .Modify() method to specify which properties you want updated with what data. finally call the .ExecuteAsync() method to run the update command which will take place remotely on the database server.

Update by ID

if you'd like to update a single entity, simply target it by ID like below:

await DB.Update<Author>()
        .MatchID("xxxxxxxxxxx")
        .Modify(a => a.Surname, "The Broken")
        .ExecuteAsync();

Update by matching with filters

you can use filter definition builder methods to match entities. all of the filters of the official driver are available for use as follows.

await DB.Update<Author>()
        .Match(f=> f.Eq(a=>a.Surname,"Stark") & f.Gt(a=>a.Age,35))
        .Modify(a => a.Name, "Brandon")
        .ExecuteAsync();

Update with builder methods

also you can use all the update definition builder methods supplied by the mongodb driver like so:

await DB.Update<Author>()
        .Match(a => a.ID == "xxxxxxx")
        .Modify(x => x.Inc(a => a.Age, 10))
        .Modify(x => x.Set(a => a.Name, "Brandon"))
        .Modify(x => x.CurrentDate(a => a.ModifiedOn))
        .ExecuteAsync();

Update all properties

instead of specifying each and every property with .Modify() you can simply supply a complete entity using .ModifyWith(). all properties of the matched documents will be updated with the corresponding property values of the supplied entity instance.

await DB.Update<Book>()
        .MatchID("xxxxxxxxxxxxx")
        .ModifyWith(book)
        .ExecuteAsync();

Update only a few specified properties

you can specify a couple of properties to be updated with the corresponding values from a supplied entity instance like below.

await DB.Update<Book>()
        .MatchID("xxxxxxxxxxxxx")
        .ModifyOnly(b => new { b.Title, b.Price }, book)
        .ExecuteAsync();

in the above example, only the Title and Price of the matched book will be updated in the database.

Update all others except for the specified properties

you can update all other properties than the specified properties with the corresponding values from the supplied entity instance like so:

await DB.Update<Book>()
        .MatchID("xxxxxxxxxxxxx")
        .ModifyExcept(b => new { b.Price, b.ISBN }, book)
        .ExecuteAsync();

in the above example, all other properties except the Price and ISBN are updated with the values from the book instance.

Bulk updates

var bulkUpdate = DB.Update<Author>();

bulkUpdate.Match(a => a.Age > 25)
          .Modify(a => a.Age, 35)
          .AddToQueue();

bulkUpdate.Match(a => a.Sex == "Male")
          .Modify(a => a.Sex, "Female")
          .AddToQueue();

await bulkUpdate.ExecuteAsync();

first get a reference to a Update<T> class. then specify matching criteria with Match() method and modifications with Modify() method just like you would with a regular update. then instead of calling ExecuteAsync(), simply call AddToQueue() in order to queue it up for batch execution. when you are ready to commit the updates, call ExecuteAsync() which will issue a single bulkWrite command to the database.

Update and retrieve

in order to update an entity and retrieve the updated enity, use the .UpdateAndGet<T>() method on the DB class like so:

var result = await DB.UpdateAndGet<Book>()
                     .Match(b => b.ID == "xxxxxxxxxxxxx")
                     .Modify(b => b.Title, "updated title")
                     .ExecuteAsync();

Update and retrieve with projection

projection of the returned entity is possible using the .Project() method before calling .ExecuteAsync().

var result = await DB.UpdateAndGet<Book>()
                     .Match(b => b.ID == "xxxxxxxxxxxxx")
                     .Modify(b => b.Title, "updated title")
                     .Project(b => new Book { Title = b.Title })
                     .ExecuteAsync();

you can also project the result to a completely different type using the generic overload like so:

var result = await DB.UpdateAndGet<Book, decimal>()
                     .Match(b => b.ID == "xxxxxxxxxxxxx")
                     .Modify(b => b.Title, "updated title")
                     .Project(b => b.Price)
                     .ExecuteAsync();

Aggregation pipeline updates

starting from mongodb sever v4.2, we can refer to existing fields of the documents when updating as described here.

the following example does 3 things.

creates a 'FullName' field by concatenating the values from 'FirstName' and 'LastName' fields.
creates a 'LowerCaseEmail' field by getting the value from 'Email' field and lower-casing it.
removes the Email field.

await DB.Update<Author>()
        .Match(_ => true)
        .WithPipelineStage("{ $set: { FullName: { $concat: ['$FirstName',' ','$LastName'] }}}")
        .WithPipelineStage("{ $set: { LowerCaseEmail: { $toLower: '$Email' } } }")
        .WithPipelineStage("{ $unset: 'Email'}")
        .ExecutePipelineAsync();

note: pipeline updates and regular updates cannot be used together in one command as it's not supported by the official c# driver.

Array filter updates

await DB.Update<Book>()
        .Match(_ => true)
        .WithArrayFilter("{ 'x.Age' : { $gte : 30 } }")
        .Modify("{ $set : { 'Authors.$[x].Age' : 25 } }")
        .ExecuteAsync();

the above update command will set the age of all authors of books where the age is 30 years or older to 25. refer to this document for more info on array filters.