在Linq和Entity Framework Core中使用内联表值函数 [英] Use a Inline Table-Valued Functions with Linq and Entity Framework Core

问题描述

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(出于讨论目的而简化查询):

I created an Inline Table-Valued Functions (ITVF) in SQL Server that returns a table of values (query simplified for discussion purposes):

CREATE FUNCTION dbo.VehicleRepairStatus()
RETURNS TABLE
AS
   RETURN
       SELECT VehicleID, CurrentStatus 
       FROM VehicleRepairHistory
       ...

我可以在查询中引用哪些内容

Which I can reference in a query:

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:

I'd like to be able to use it in Linq query:

var vehicles = await _databaseContext.Vehicles
    .Join() // join ITVF here?
    .Where(v => v.Type == 'Bus' )
    .OrderBy(v => v.Name)
    .ToAsyncList();

在某些时候，我可能会更改ITVF以包含一个参数:

At some point, I may change the ITVF to include a parameter:

CREATE FUNCTION dbo.VehicleRepairStatus(@id AS INT)
RETURNS TABLE
AS
RETURN

  SELECT VehicleID, CurrentStatus 
  FROM   VehicleRepairHistory
  ...
  WHERE  VehicleID = @id

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?

Is either approach possible?

推荐答案

是的，可以利用EF Core 2.1引入的

Yes, it's possible by utilizing the EF Core 2.1 introduced query types. Following are the required steps:

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):

First, create a class to hold the TVF record (update it with the correct data types):

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:

Then expose it from your db context using a combination of Query and FromSql methods:

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:

Now you can use it inside your LINQ queries like any other IQueryable<T> returning method, for instance:

from v in db.Vehicles
from r in db.VehicleRepairStatus(v.ID)
select new { v.ID, v.Name, r.CurrentStatus }

FromSql方法中的选择"使其成为可组合，因此整个查询都转换为SQL并在服务器端执行.

The "select" inside FromSql method makes it composable, so the whole query is translated to SQL and executed server side.

更新:实际上，如上例所示，当用作相关子查询时，这是行不通的(请参阅).仅当传递常量/变量参数(如

Update: Actually this doesn't work when used as correlated subquery like the above example (see Reference to an ITVF raises a "second operation started on this context before a previous operation completed" exception). It could be used only if passing constant/variable parameters like

from r in db.VehicleRepairStatus(123)
...

请参阅链接中后续帖子的答案，以正确执行相关查询方案.

See the answer to the follow up post from the link for correct implementation for correlated query scenarios.

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