I've done multiple projects using the Repository pattern(Interface=>Repository)but now, I'm facing a new challenge(not a big one) with one of my coworker's code. We are implementing a Generic service that contains all of the CRUD operations methods for all entity classes.
We are using Database first in this project, and have the following structure,
aspx.cs > entityclass(AppUser) > Generic Service > Entity model.
public class UserServices : GenericServices<User>
{ //Implemented methods }
And this as the Generic Service:
public class GenericServices<T> where T : class
{
App_dbEntities _db;
IDbSet<T> ent;
public GenericServices()
{
_db = new App_dbEntities();
ent = _db.Set<T>();
}
public IEnumerable<T> Select()
{
return ent;
}
public T Select(string id)
{
??
}
}
I'm trying to handle the entities's properties but since this is Generic, it doesn't know what entity am handling at the moment. I've seen some examples using predicate as a function parameter. Please give me a hand.
If you want flexibility and are willing to use expressions as your predicate
public virtual T Select(Expression<Func<T, bool>> predicate)
{
return _dbSet.FirstOrDefault(predicate);
}
Usage
var service = new AppUserServices();
var appUser = service.Select(s=> s.CompositeKey1 == "some_value" && s.CompositeKey2 == "some_other_value");
var appUser2 = service.Select(s=> s.IntProperty == 100 && s.AnotherStringProperty == "some_other_value");
Agreed with @Thomas, you can use Find
method as I show below:
public virtual T Select(params object[] keyValues)
{
return ent.Find(keyValues);
}
This way you can also find entities with composite primary keys. I suggest to take a look to this codeplex project, you will find an implementation of Repository, UnitOfWork, and also Service pattern. It's going to give you good ideas.