Am I misunderstanding the usage?

[ByZhouhang]

public class User:
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }

     [Projectable] 
     public string FullName => LastName + " / " + FirstName;

    }

// want  wirte like this  
_userRepository.Where(t => t.FullName .Contains("CC")).First()    //Translation of member 'FullName' on entity type 'User' failed

_userRepository.Select(t => t.FullName).First()  //will cause  query for all fields  (not   LastName FirstName  two filed)

[koenbeuk]

You'll have to enable Projectables within your DbContext:

e.g. in case of DI:

services.AddDbContext<ApplicationDbContext>(options => {
      options
          .UseSqlite(dbConnection)
          .UseProjectables() // Add this line
  })

[ByZhouhang]

You'll have to enable Projectables within your DbContext:

e.g. in case of DI:

services.AddDbContext<ApplicationDbContext>(options => {
      options
          .UseSqlite(dbConnection)
          .UseProjectables() // Add this line
  })

thanks，The reason for the difference is ？
1、[Projectable] public string FullName => LastName + " / " + FirstName;
2、[Projectable] public string FullName => => $"{LastName} / {FirstName}"
_userRepository.Where(t => t.FullName .Contains("CC")).First() // 2. will error can not translate string.formate

[koenbeuk]

@ByZhouhang

EF Core does not support string interpolation (String.Format), this library does not change that fact, see: dotnet/efcore#6532 (comment)