从实体框架调用UDF时出错LINQ查询

Question

我遇到了LINQ查询调用用户定义函数的问题。我正在使用.NET 4.0框架和VS 2010.下面是edmx函数定义的XML快照。

<Schema Namespace="MystoreDWModel.Store" Alias="Self" Provider="System.Data.SqlClient" ProviderManifestToken="2008" xmlns:store="http://schemas.microsoft.com/ado/2007/12/edm/EntityStoreSchemaGenerator" xmlns="http://schemas.microsoft.com/ado/2009/02/edm/ssdl"> 
    <Function Name="RegularPrice" store:Name="RegularPrice" IsComposable="true" Schema ="MystoreDWExtension.mystore" Aggregate="false" BuiltIn="false" ReturnType="decimal" StoreFunctionName="fn_GetPrice"> 
     <Parameter Name="ProductID" Type="varchar" Scale="40" Mode="In"/> 
     <Parameter Name="PriceTypeID" Type="varchar" Scale="10" Mode="In"/> 
     <Parameter Name="GroupCode" Type="varchar" Scale="10" Mode="In"/> 
     <Parameter Name="GroupValue" Type="varchar" Scale="10" Mode="In"/> 
     <Parameter Name="EffectiveDate" Type="datetime" Mode="In"/> 
    </Function> 

我在代码中定义下面的函数存根...

[EdmFunction("MystoreDWModel.Store", "RegularPrice")] 
public decimal? RegularPrice(
    string ProductID, 
    string PriceTypeID, 
    string GroupCode, 
    string GroupValue, 
    DateTime EffectiveDate) 
{ 
    throw new NotImplementedException("You can only call this method as part of a LINQ expression"); 
} 

，我使用访问功能如下呼叫...

MystoreDWEntities4 test = new MystoreDWEntities4(); 

var prices = (from products in test.Products 
       select RegularPrice("PRODUCTID", "R", "D", "20", DateTime.Now)); 

当我尝试访问价格数据时，我收到以下错误...

The specified method 
'System.Nullable`1[System.Decimal] RegularPrice 
(System.String, System.String, System.String, System.String, System.DateTime)' 
on the type 'EntityFrameworkTest.Form1' cannot be translated 
into a LINQ to Entities store expression because the instance 
over which it is invoked is not the ObjectContext over which 
the query in which it is used is evaluated. 

我已经尝试了几种变体的配置，并且无济于事。以前有没有人跑过这个错误，我可以用什么步骤来修复它？

Answer 1

尝试放置RegularPrice方法进MystoreDWEntities4类定义（使用像在下面的示例部分声明）：

public partial class MystoreDWEntities4 { 
    [EdmFunction("MystoreDWModel.Store", "RegularPrice")] 
    public decimal? RegularPrice(
    string ProductID, 
    string PriceTypeID, 
    string GroupCode, 
    string GroupValue, 
    DateTime EffectiveDate) 
    { 
    throw new NotImplementedException("You can only call this method as part of a LINQ expression"); 
    } 
} 

然后调用它作为ObjectContext的实例方法，如这里：

ObjectSet<Products> products = test.Products; 
var prices = from prod in products 
      select new { Price = test.RegularPrice("PRODUCTID", "R", "D", "20", DateTime.Now)}; 

Answer 2

将该方法定义为扩展方法，而不是普通的普通方法。

http://jendaperl.blogspot.com/2010/11/specified-method-xxx-on-type-yyy-cannot.html