var query = db.Incidents
.Where(x => x.IsAttendanceIncident == "Y")
.GroupBy(x => new { x.EmployeeId, x.DateOfIncident, x.IsAttendanceIncident })
示例1:
.Select(x => x.FirstOrDefault()); // your original code which retrieves entities to not delete
var dupes = db.Incidents.Except( query ); // get entities to delete
示例2:
.SelectMany( x => x.OrderBy( y => y.Id ).Skip(1) ); // gets dupes directly
var dupes = query; // already have what we need
最后:
foreach( var dupe in dupes )
{
db.Incidents.Remove( dupe );
}
从我之前使用的测试上下文生成的示例 SQL,其中 Person 实体与手表具有 1:N 关系:
C#:
context.Persons.SelectMany(x => x.Watches.OrderBy(y => y.Id).Skip(1))
生成的SQL:
SELECT
1 AS [C1],
[Skip1].[Id] AS [Id],
[Skip1].[Brand] AS [Brand],
[Skip1].[Person_Id] AS [Person_Id]
FROM [dbo].[Persons] AS [Extent1]
CROSS APPLY (SELECT [Project1].[Id] AS [Id], [Project1].[Brand] AS [Brand], [Project1].[Person_Id] AS [Person_Id]
FROM ( SELECT [Project1].[Id] AS [Id], [Project1].[Brand] AS [Brand], [Project1].[Person_Id] AS [Person_Id], row_number() OVER (ORDER BY [Project1].[Id] ASC) AS [row_number]
FROM ( SELECT
[Extent2].[Id] AS [Id],
[Extent2].[Brand] AS [Brand],
[Extent2].[Person_Id] AS [Person_Id]
FROM [dbo].[Watches] AS [Extent2]
WHERE [Extent1].[Id] = [Extent2].[Person_Id]
) AS [Project1]
) AS [Project1]
WHERE [Project1].[row_number] > 1 ) AS [Skip1]