如何使用 RIA 服务将 SQL 查询转换为 LINQ？

发布于 2024-11-25 01:14:07 字数 1063 浏览 2 评论 0原文

我从一个针对视图和视图进行选择的 SQL 查询开始。看起来像这样：

SET @id = ...
SET @variableDate = ...
SELECT Id,
        dbo.fnGreaterDateTime(ViewDate,@variableDate) AS GreaterDate,
    FROM vwExample
    WHERE Id = @id

SQL 函数 fnGreaterDateTime 按您的预期工作，返回传入的两个值中较大的一个。

在使用 EF & 时，我无法将其转换为 LINQ 查询。 RIA 服务。在我的域服务中，我希望能够执行如下操作：

public IQueryable<ExampleViewResult> GetExampleViewResults(int id, DateTime variableDate)
{

    var query = from r in this.ObjectContext.ExampleViewResults
        where r.Id == id
        select new ExampleViewResult
          { 
            Id = r.Id,
            ViewDate = (r.ViewDate > variableDate) ? r.ViewDate : variableDate
          }
    return query;
}

但是当我调用此方法时，我收到一条错误，指出“无法在 LINQ to Entities 查询中构造实体或复杂类型 ExampleViewResult”。

我尝试遵循this 线程，但是当我让域服务方法返回 DTO 列表时，自动代码生成不包括在我的域上下文中使用的方法。

有什么想法吗？

原文

I'm starting with a SQL query that selects against a view & looks like this:

SET @id = ...
SET @variableDate = ...
SELECT Id,
        dbo.fnGreaterDateTime(ViewDate,@variableDate) AS GreaterDate,
    FROM vwExample
    WHERE Id = @id

The SQL function fnGreaterDateTime works as you would expect, returning the greater of the two values passed in.

I'm having trouble converting this to a LINQ query when using EF & RIA services. In my Domain Service, I would like to be able to do something like the following:

public IQueryable<ExampleViewResult> GetExampleViewResults(int id, DateTime variableDate)
{

    var query = from r in this.ObjectContext.ExampleViewResults
        where r.Id == id
        select new ExampleViewResult
          { 
            Id = r.Id,
            ViewDate = (r.ViewDate > variableDate) ? r.ViewDate : variableDate
          }
    return query;
}

But when I call this method I receive an error that says "The entity or complex type ExampleViewResult cannot be constructed in a LINQ to Entities query".

I tried following some advice over in this thread, but when I have the domain service method return a list of DTOs instead, the auto-code generation doesn't include the method for use in my domain context.

Any ideas?

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