[melolife]

It's a hard problem, NHibernate actually came a little bit closer with it's QueryOver API. The most glaring problem with the LINQ API is there is no way to OR two reusable conditions together because the only tool you have is Where.

To be clear you can get a long way by abusing EF's willingness to try and interpret arbitrarily complex expressions - it just provides zero tooling or guidance on how to build those expressions.

Or projections. It's possible to write a reusable projection for EF like so:

    class MyTableProjection {
      public static Expression<Func<MyTable, MyTableProjection>> Expression =>
        t => new MyTableProjection {
       Id = t.Id,
       Str = t.Str,
       Flag = t.Flag
     };
    
      public int Id { get; init; }
      public string Str { get; init; }
      public bool Flag { get; init; }
    }
    
    dbContext.MyTable
    .Where(...)
    .Select(MyProjection.Expression)
    .ToListAsync()
    

But I have never seen anyone do this because it breaks the promise that you magically won't have to write any code or abstractions.

[nightski]

It's pretty easy using LinqKit [1]. Just PredicateBuilder.Or() [2]. If you were to try and implement PredicateBuilder yourself that requires a little more knowledge around expressions, but it's worth learning and opens up a lot more possibilities.

[1] https://github.com/scottksmith95/LINQKit [2] http://www.albahari.com/nutshell/predicatebuilder.aspx

[pacoWebConsult]

Automapper solves this. Composable projections to your DTOs/ endpoint return types. You can do some very powerful things with it. For example, in a past project I encrypted/unencrypted a property containing a secure message by defining a function to do so and setting up Automapper to automatically apply the function when mapping to/from the DTO that is sent/received by the API.