实体框架数据库查询结果为NULL值

Question

I am creating a WPF app using C#, Entity Framework and SQL Server 2008 R2. I am trying to fire the following query.

Select Convert(nvarchar(10),bk.BookingDate,103) as Date, Count(*) 
from Booking bk
where  
    Convert(date,bk.BookingDate) between '2014-10-01' and '2014-10-31'
    and bk.IsDeleted = 0
group by Convert(nvarchar(10),bk.BookingDate,103)
order by 1

This query works if directly fired on SQL Server prompt and fetches results. However when I am trying using Entity Framework I am getting NULL value.

var values = context.Database
    .SqlQuery<KeyValuePair<string, int>>(query)
    .ToList<KeyValuePair<string, int>>();

1. Is it because I am using a KeyValue pair in the method call?
2. Is there any alternative of doing this using Entity Framework?
3. Or should I use old style database connection and command to run this query?

Answer 1

I think this is because you're using the KeyValuePair<> , try creating a simple class like:

public class MyResult
{
    public DateTime Date { get; set; }
    public int TotalCount { get; set; }
}

And add count(*) as TotalCount to your query. And use that as the generic type parameter for your SqlQuery call. A key thing to remember is that EF will look for members on the result type with names that match the columns returned from the query. So as an example, if your query returned a column called "total_count", you would need a property on your class also called "total_count" (with the underscore).