C# MongoDB Driver - How to use UpdateDefinitionBuilder?

I looked up a way to work with mongodb's UpdateDefinitionBuilders but the documentation doesn't really show much...

I need to be able to dynamically build my update queries, so I thought about doing it like this:

var update = Builders<Product>.Update;

update.Set("add A update");

if ()
    update.Set("add X update");
else
    update.Set("add Y update");

update.Set("add B update");

if ()
    update.Set("add Z update");
else
    update.Set("add P update");

Collection.UpdateOneAsync(filter, update, updateOptions);

But it gives a compilation error:

cannot convert from UpdateDefinitionBuilder UpdateDefinition

I looked, but couldn't find, a solution how to works with this UpdateDefinitionBuilders

Can someone please give a code sample of how to use this class?

Solution

If you need to simply update multiple properties you can call Set on update builder and then make subsequent call to Set extension methods. You can either use lambda expression or property name.

var update = Builders<Product>.Update
    .Set(p => Name, "Name value")
    .Set(p => Description, "Description value");

collection.UpdateOneAsync(filter, update, updateOptions);

If you want conditionally update some properties you should create a collection of the updates and then combine them:

var update = Builders<Product>.Update;
var updates = new List<UpdateDefinition<Product>>();

updates.Add(update.Set("propertyA", "add A update"));

if (isX)
    updates.Add(update.Set("propertyX", "add X update"));
else
    updates.Add(update.Set("propertyY", "add Y update"));

updates.Add(update.Set(p => p.PropertyB, "add B update"));

if (isZ)
    updates.Add(update.Set(p => p.PropertyZ, "add Z update"));
else
    updates.Add(update.Set(p => p.PropertyP, "add P update"));

await Collection.UpdateOneAsync(filter, update.Combine(updates), updateOptions);