实体框架中的不同记录

Question

I want to Distinct List of Data

My Code:

PendingGRemsResult _Return = new PendingGRemsResult();

_Return.PendingGRemsResultRecord = Context.Where(a => a.Status == 0)
   .Select(s => new PendingGRemsResultRecord
     { GUID = s.GRemGUID.GUID,
       Count = App.GroupedRemittance
         .GetByFilter((gr => gr.GRemGUID.GUID == s.GRemGUID.GUID))
         .Count(),
       CreatorType = s.GRemGUID.CreatorType.Value})
  .Distinct()
  .ToList();

return _Return;

this code not working data sill duplicated

Answer 1

There are at least 3 solutions to this challenge:

1. Use DistinctBy() method with lambda expression, example:

   var query = someData.DistinctBy(x => x.PropertyYouWantToDistinquishBy) ;

2. Build an equalityComparer that will implement the interface IEqulityComparer<PendingGRemsResultRecord> and then use an instance of this class for the overload od Distinct() method.

3. Implement the IEquatable interface in your PendingGRemsResultRecord class (with Equals and GetHashCode methods).

Answer 2

_Return.PendingGRemsResultRecord = 
     Context.Where(a => a.Status == 0)
            .Select(a => new {
               a.GRemGUID.GUID, 
               CreatorType = a.s.GRemGUID.CreatorType.Value })
            .Distinct()
            .Select(x => new PendingGRemsResultRecord {
                  GUID = x.GUID,
                  Count = App.GroupedRemittance
                             .GetByFilter(gr => gr.GRemGUID.GUID == x.GUID)
                             .Count(),
                  CreatorType = x.CreatorType
              }).ToList();

UPDATE: How it works - thus you don't have Equals and GetHashCode specified on you PendingGRemsResultRecord class, then instances of this class will be compared by reference. And that will treat all instances to be different, even if they have same values of properties. You have several possibilities to teach Distinct() method to look on values instead of comparing references (override Equals and GetHasCode , create and pass custom comparer) but you also can use power of anonymous objects, which have default Equals and GetHashCode implementations that use values of properties to check if two anonymous objects are equal.

That's exactly what I use here - projecting source sequence objects into anonymous objects with GUID and CreatorType properties. Then with power of default comparison of anonymous objects you can use Distinct() to get only objects with different guid and creator type. Next is simple projecting of distinct results to your PendingGRemsResultRecord .