Does adding [NotMapped] to a partial class avoid mapping the entire class?

Question

I have set up my EF code-first database but want to add additional derived properties. (Yes, it should be in a view model, we can discuss another time why it is this way.) I have created a partial class extending the actual table class. If I add a [NotMapped] to the new partial, will it avoid mapping the additional properties I add there or will it apply to the entire class?

Answer 1

It will apply to the entire class. Remember that a partial class is simply a way of splitting a class into multiple files. From the official docs:

At compile time, attributes of partial-type definitions are merged.

So this:

[SomeAttribute]
partial class PartialEntity
{
    public string Title { get; set; }
}

[AnotherAttribute]
partial class PartialEntity 
{
    public string Name { get; set; }
}

Is equivalent to writing:

[SomeAttribute]
[AnotherAttribute]
partial class PartialEntity
{
    public string Title { get; set; }
    public string Name { get; set; }
}

If you want to add a partial class without having the properties included in the model, you will need to add the NotMapped attribute to the individual items:

partial class PartialEntity
{
    public string Title { get; set; }
}

partial class PartialEntity 
{
    [NotMapped]
    public string Name { get; set; }
}