我可以在 Entity Framework Code First 中使用来自我的域模型的谓词吗？

Question

I've got a class with a bool method, eg:

public bool IsInFuture()
{ return this.Date > DateTime.Now; }

And I store it in a database using EF Code First. If I'll try to use that predicate in Linq operations, I'll get an exception, as it can not be translated into SQL:

await context.Where(order => order.IsInFuture()).ToListAsync();

That predicate's logic can be rather complicated and I wouldn't like to duplicate it in my code. It there any way I can "inline" it's code into Linq operations? I'm pretty sure, this problem has a solution.

Thanks in advance!

Answer 1

You can't use the predicate directly. How should EF know how to convert it into an SQL WHERE statement?

You have a few alternatives:

• Rephrase the query to use standard operations, eg smaller-than. This will duplicate the logic from the predicate, though.
• Use a raw SQL query. This will also duplicate the logic, but in SQL.
• Load the entire list of entities and then filter in-memory (ie Where() after ToList() ). Like this, you can reuse the predicate. Note that this only a good idea for very small data sets.