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从实体框架Linq查询调用UDF时出错

user-defined-functions entity-framework-4 linq

Scott Vercuski · 技术社区 · 14 年前

我遇到了一个从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Vs2010。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>

我在代码中定义了以下函数存根…

[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");
}

我用来访问函数的调用如下…

 MystoreDWEntities4 test = new MystoreDWEntities4();

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

当我试图访问价格数据时,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.

我尝试了几种不同的配置和调用,但都无效。以前有人遇到过这个错误吗?我可以使用什么步骤来修复它?

2 回复 | 直到 14 年前

Devart 14 年前

尝试将RegularPrice方法放入myStoredWentities4类定义中(使用部分声明,如下例所示):

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实例方法,如下所示:

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

Jenda 14 年前

将方法定义为扩展方法,而不是普通的老方法。

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