Linq Count() for IQueryable vs Linq Count() for IEnumerable-CodePudding

I am confused to understand the difference between Linq's Count() for IQueryable and Linq's Count() for IEnumerable.

I have the following method which has to return the same result of the counts, but enumerableCount equals 2 while queryableCount is 0:

public List<int> GetMembersCount() 
{
    var queryableQuery = MemberRepository.GetAll().Include(p => p.Message);
    var enumerableQuery = MemberRepository.GetAll().Include(p => p.Message).ToList();

    var queryableCount = queryableQuery.Count(m => m.Message.Deadline.Date == DateTime.Today);
    var enumerableCount = enumerableQuery.Count(m => m.Message.Deadline.Date == DateTime.Today);

    return new List<int>
        {
            enumerableCount,
            queryableCount
        };
}

Can anybody explain what is going on? I am using PostgreSQL and Entity Framework

CodePudding user response：

Try

var querableCount = querableQuery
    .Count(m => DbFunctions.TruncateTime(m.Message.Deadline) == DbFunctions.TruncateTime(DateTime.Now));

because DateTime.Date doesn't seem to be supported in EF if used in lambda expressions: https://stackoverflow.com/a/21825268/284240

CodePudding user response：

I don't use dates in filtering due to problems I've had in the past.

var dt = DateTime.Today;
var dt_ole = Convert.ToInt32(dt.ToOADate());
var queryableCount = queryableQuery.Count(m => SqlFunctions.DateDiff("DD", "1899-12-30", m.Message.Deadline) == dt_ole);