如何将带有linq的标量值函数用于实体？

Question

我有一个标量函数，它获取两点之间的距离，我想用它来查询最接近点的记录。标量函数与linq to sql一起使用，但对EF失败

标量函数

USE [GeoData]
GO

/****** Object:  UserDefinedFunction [dbo].[DistanceBetween]    Script Date: 09/18/2012 19:40:44 ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO



CREATE FUNCTION [dbo].[DistanceBetween](@Lat1 as real,
@Long1 as real, @Lat2 as real, @Long2 as real)
RETURNS real
AS
BEGIN

DECLARE @dLat1InRad as float(53);
SET @dLat1InRad = @Lat1;
DECLARE @dLong1InRad as float(53);
SET @dLong1InRad = @Long1;
DECLARE @dLat2InRad as float(53);
SET @dLat2InRad = @Lat2;
DECLARE @dLong2InRad as float(53);
SET @dLong2InRad = @Long2 ;

DECLARE @dLongitude as float(53);
SET @dLongitude = @dLong2InRad - @dLong1InRad;
DECLARE @dLatitude as float(53);
SET @dLatitude = @dLat2InRad - @dLat1InRad;
/* Intermediate result a. */
DECLARE @a as float(53);
SET @a = SQUARE (SIN (@dLatitude / 2.0)) + COS (@dLat1InRad)
* COS (@dLat2InRad)
* SQUARE(SIN (@dLongitude / 2.0));
/* Intermediate result c (great circle distance in Radians). */
DECLARE @c as real;
SET @c = 2.0 * ATN2 (SQRT (@a), SQRT (1.0 - @a));
DECLARE @kEarthRadius as real;
/* SET kEarthRadius = 3956.0 miles */
SET @kEarthRadius = 6376.5;        /* kms */

DECLARE @dDistance as real;
SET @dDistance = @kEarthRadius * @c;
return (@dDistance);
END

GO

我添加了一个ado.net实体模型，从数据库中更新了模型，并选择了

 <Function Name="DistanceBetween" ReturnType="real" Aggregate="false" BuiltIn="false" NiladicFunction="false" IsComposable="true" ParameterTypeSemantics="AllowImplicitConversion" Schema="dbo">
      <Parameter Name="Lat1" Type="real" Mode="In" />
      <Parameter Name="Long1" Type="real" Mode="In" />
      <Parameter Name="Lat2" Type="real" Mode="In" />
      <Parameter Name="Long2" Type="real" Mode="In" />
    </Function>

我做了一个局部类并写了这个方法

public partial class GeoDataEntities
{
    [EdmFunction("GeoDataModel.Store", "DistanceBetween")]
    public double DistanceBetween(double lat1, double lon1, double lat2, double lon2)
    {
        throw new NotImplementedException();
    }
}

我尝试了很多次，用此代码查询函数，但出现错误

var NParcel = db.geoAddresses.Where(g=> db.DistanceBetween(21.5,39.5, g.lat,g.lon) < 20);

当我尝试count或foreachNParcel时出现此错误

类型为’EFSample.GeoDataEntities’的指定方法’Double
DistanceBetween（Double，Double，Double，Double）’无法转换为LINQ to Entities存储表达式。

和stacktrace

在System.Data.Objects.ELinq.ExpressionConverter.ThrowUnresolvableFunction（Expression
Expression）处System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.FunctionCallTranslator.TranslateFunctionCall（ExpressionConverter
parent，MethodCallExpression call，EdmFunctionAttribute
functionAttribute）在System.Data.Objects.ELinq
System.Data.Objects.ELinq.ExpressionConverter.BinaryTranslator.TypedTranslate（ExpressionConverter父代，BinaryExpression
linq）在System.Data.Objects.ELinq.ExpressionConion（Expression）（ExpressionConverter。在System.Data.Objects.ELinq处，位于System.Data.Objects.ELinq.ExpressionConverter.TranslateLambda（LambdaExpression
lambda，DbExpression输入）处。ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate（ExpressionConverter父，MethodCallExpression调用，DbExpression＆源，DbExpressionBinding＆sourceBinding，DbExpression＆lambda）位于System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate（ExpressionConverter
.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate（ExpressionConverter父类，System.Data.Objects.ELinq.ExpressionConverter.TranslateExpression（Expression
linq）在System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.AggregateTranslator。在System.Data.Objects.ELinq.ExpressionConverter处调用ExpressionConverter的父方法（调用MethodCallExpression）。System.Data.Objects.ELinq.ExpressionConverter.Convert（）（System.Data.Objects.ELinq.ELinqQueryState.GetExecutionPlan（Nullable）处的MethodCallTranslator.TypedTranslate（ExpressionConverter
parent，MethodCallExpression linq）1 forMergeOption) at System.Data.Objects.ObjectQuery1.GetResults（Nullable，1 forMergeOption) at System.Data.Objects.ObjectQuery位于System.Linq.Enumerable.Single
[TSource]中的System.Collections.Generic.IEnumerable.GetEnumerator（）（IEnumerable
1 source) at System.Linq.Queryable.Count[TSource](IQueryable1源）

Answer 1

这是您的操作方式：

第1步：在edmx中

      <Function Name="DistanceBetween" Aggregate="false" BuiltIn="false" NiladicFunction="false" IsComposable="false" ParameterTypeSemantics="AllowImplicitConversion" Schema="dbo">
      <CommandText>
        select dbo.DistanceBetween(@lat1,@long1,@lat2,@long2)
      </CommandText>
      <Parameter Name="Lat1" Type="real" Mode="In" />
      <Parameter Name="Long1" Type="real" Mode="In" />
      <Parameter Name="Lat2" Type="real" Mode="In" />
      <Parameter Name="Long2" Type="real" Mode="In" />
    </Function>

步骤2：导入功能

1. 双击 edmx
2. 在“模型浏览器”视图中，展开GeoDataModel.Store（可以命名为不同）
3. 扩张 stored procedures /function
4. 连按两下 DistanceBetween
5. Scalars = Single
6. 点击确定

步骤3：在C＃中：

    GeoDataEntities db = new GeoDataEntities();
    var first = db.DistanceBetween(234, 2342, 424, 243).First().Value;

请注意 ， IsComposable="false"不ReturnType，不要忘记添加：

      <CommandText>
        select dbo.DistanceBetween(@lat1,@long1,@lat2,@long2)
      </CommandText>

希望能有所帮助。