Question

I’m implementing the service \ repository pattern in a new project. I’ve got a base interface that looks like this. Everything works great until I need to use the GetMany method. I’m just not sure how to pass a LINQ expression into the GetMany method. For example how would I simply sort a list of objects of type name?

nameRepository.GetMany( ? )

public interface IRepository<T> where T : class
{
    void Add(T entity);
    void Update(T entity);
    void Delete(T entity);
    void Delete(Expression<Func<T, bool>> where);
    T GetById(long Id);
    T GetById(string Id);
    T Get(Expression<Func<T, bool>> where);
    IEnumerable<T> GetAll();
    IEnumerable<T> GetMany(Expression<Func<T, bool>> where);

}



 public virtual IEnumerable<T> GetMany(Expression<Func<T, bool>> where)
 {
    return dbset.Where(where).ToList();
 }

Answer 1

Assuming that you had an implementation of IRepository<MyClass>, you would make a call to GetMany like so:

IRepository<MyClass> repository = ...;

IEnumerable<MyClass> filtered = repository.GetMany(
    mc => true);

Note the mc => true lambda expression. mc in this case is the parameter (in this case, of type MyClass) passed to the Expression<Func<T, bool>> which will be evaluated (one would assume through an IQueryable<T>) and the mc.SomeProperty == someValue is an expression which returns true, which is the second type parameter of the Expression<Func<T, bool>>.

Once you have the filtered, you can use the order by clause (or the OrderBy extension method, they’re the same) to sort the results, like so:

var filteredAndOrdered = filtered.OrderBy(mc => mc.MyProperty);

Note that GetMany returns an IEnumerable<T>, not an IQueryable<T>; this is important if your result set is large, as the ordering will happen on the client, and not be sent to the server.

For an OrderBy operation, this can be expensive because it has to go through the entire sequence (to order) before returning the first result.