Question

I often see example repository patterns that look like this:

public interface IRepository<T>
{
    T GetById(int id);
    IEnumerable<T> GetAllByName(string name);
}

But how do you handle cases where you may need to do a complex search? I don’t think it would be a good idea to add many methods to the interface that would make it end up looking like:

IEnumerable<T> GetAllByFirstName(string name);
IEnumerable<T> GetAllByLastName(string name);
IEnumerable<T> GetAllByFirstAndLastName(string name);
IEnumerable<T> GetAllByAddress(string name);
...
...
...

Answer 1

Use the Predicate Builder to dynamically build the where condition

public interface IRepository<T>
{
    T GetById(int id);

    IEnumerable<T> GetAllBy(Expression<Func<T, bool>> predicate);
}

Then build the conditions

  var predicate = PredicateBuilder.True<Customer>();
  if (!string.IsNullOrEmpty(FirstName))
  {
       predicate = predicate.And(d => d.FirstName.Contains(FirstName));
  }

  if (!string.IsNullOrEmpty(LastName))
  {
       predicate = predicate.And(d => d.LastName.Contains(LastName));
  }

  var products = productRepo.GetAllBy(predicate);

Create a class to pass the search criteria

public class CustomerFilterCriteria
{
    public string FirstName { get; set; }

    public string LastName { get; set; }

    public string Address { get; set; }

}

public interface IRepository<T>
{
    T GetById(int id);
    IEnumerable<T> GetAllBy(CustomerFilterCriteria criteria);
}