使用 EF Core 3.1 通过不可翻译的方法进行过滤

Question

In a web application with a SQL Server database, I have implemented the data access layer using the "Repository Pattern". For filtering a User based on its email, I'm using an expression like this:

var emailFilter = "user@example.com";
var query = _dbContext.Set<User>().Where(x => x.Email.Normalize() == emailFilter.Normalize());
var result = query.ToListAsync(); 

But EF Core throws an exception which says:

... could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync()

I have more than 200k users in the users' table and I don't want to filter data on the client-side.

The mentioned code is only an example but I mean other use cases with more complex methods.

Now, how can I use complex functions to filter data on the server-side?

Answer 1

I suggest to you, first normalize your email in db by bulk update:

by Z.EntityFramework.Plus.EFCore

_dbContext.Set<User>().update(x => new User {Email =  x.Email.Normalize()}  ;

then

emailFilter = ("user@example.com").Normalize();
var query = _dbContext.Set<User>().Where(x => x.Email  == emailFilter);
var result = query.ToListAsync(); 

it's an instance solution

Answer 2

For non standard go with plain sql queries...

var emailFilter = "user@example.com";
var result = await _dbContext.Users.FromSqlRaw($"SELECT * FROM dbo.Users WHERE LOWER(Email) = {emailFilter}").ToListAsync(); 

Or use Functions

var emailFilter = "user@example.com";
var result = await _dbContext.Users.Where(x => EF.Functions.Like(x.Email, $"%{emailFilter}%")).ToListAsync(); 

With the penalty of the performance...