[我在SQL Server中创建了一个内联表值函数(ITVF),该函数返回一个值表(出于讨论目的简化查询):
CREATE FUNCTION dbo.VehicleRepairStatus()
RETURNS TABLE
AS
RETURN
SELECT VehicleID, CurrentStatus
FROM VehicleRepairHistory
...
我可以在查询中引用:
SELECT
v.ID, v.Name,
r.CurrentStatus
FROM
Vehicle v
LEFT OUTER JOIN
dbo.VehicleRepairStatus() r on v.ID = r.VehicleID
我希望能够在Linq查询中使用它:
var vehicles = await _databaseContext.Vehicles
.Join() // join ITVF here?
.Where(v => v.Type == 'Bus' )
.OrderBy(v => v.Name)
.ToAsyncList();
[在某些时候,我可以更改ITVF以包括一个参数:
CREATE FUNCTION dbo.VehicleRepairStatus(@id AS INT)
RETURNS TABLE
AS
RETURN
SELECT VehicleID, CurrentStatus
FROM VehicleRepairHistory
...
WHERE VehicleID = @id
并且像标量一样调用:
SELECT v.ID, v.Name
,(SELECT val FROM dbo.VehicleRepairStatus(v.ID)) AS CurrentStatus
FROM Vehicle v
Linq查询:
var vehicles = await _databaseContext.Vehicles
.Select( ) // call ITVF here?
.Where(v => v.Type == 'Bus' )
.OrderBy(v => v.Name)
.ToAsyncList();
这两种方法都有可能吗?
首先,创建一个类来保存TVF记录(使用正确的数据类型对其进行更新:]
public class VehicleRepairStatus
{
public int VehicleID { get; set; }
public int CurrentStatus { get; set; }
}
然后将其注册到您的OnModelCreating
:
modelBuilder.Query<VehicleRepairStatus>();
然后使用Query
和FromSql
方法的组合从数据库上下文中公开它:
public IQueryable<VehicleRepairStatus> VehicleRepairStatus(int id) => Query<VehicleRepairStatus>().FromSql($"select * from VehicleRepairStatus({id})");
仅此而已。现在,您可以像其他任何
IQueryable<T>
返回方法一样在LINQ查询中使用它,例如:
from v in db.Vehicles from r in db.VehicleRepairStatus(v.ID) select new { v.ID, v.Name, r.CurrentStatus }
请参阅链接中后续帖子的答案,以获取相关查询方案的正确实现。FromSql
方法内部的“选择”使其变为“ [可组合,因此整个查询将转换为SQL并在服务器端执行。Update:实际上,如上例所示,当用作相关子查询时,这不起作用(请参见Reference to an ITVF raises a "second operation started on this context before a previous operation completed" exception)。仅当传递常量/变量参数,例如
时才可以使用它
from r in db.VehicleRepairStatus(123) ...