如何确定 EF 核心中的自定义服务器评估？

Question

I have this entity

public class Foo
{
   public int Id{get; private set;}
   public DateTime CreatedOn {get; private set;}
   public bool IsActive {get; private set;}
   public bool CanBeDisplayed => IsActive  && CreatedOn > DateTime.Now.AddYear(-1);
}

I want to this dbcontext.Foos.Where(f=>f.CanBeDisplayed).ToArray(); could be evaluated on the sql server side. May there is an attribute or some binding in the DBContext class who can give me a work arround. My goal is to have a Rich Model, ef core compatible, am I missing something?

Answer 1

I see two possible workarounds:

1. Introducing Computed Column and providing sql for it.
2. Making expression tree

public class Foo
{
    public int Id { get; private set; }
    public DateTime CreatedOn { get; private set; }
    public bool IsActive { get; private set; }
    // mark ignored for EF?
    public bool CanBeDisplayed => _compiled(this);

    private static Func<Foo, bool> _compiled = CanBeDisplayedExp.Compile();
    public static Expression<Func<Foo, bool>> CanBeDisplayedExp = f => f.IsActive && f.CreatedOn > DateTime.Now.AddYears(-1);
}

With usage limited to dbcontext.Foos.Where(Foo.CanBeDisplayedExp).ToArray()

Also not sure that EF can translate DateTime.Now.AddYears .

PS

Just FYI Linq2Db has expression based calculated colums and Expression Methods support.