Question

可能重复：
Can SQL level functions be made available to LINQ to Entity queries?

我有一个标量函数可以获得两点之间的距离，我想用它来查询最接近的记录点。标量函数与linq一起使用到sql但是在EF

时失败

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，从数据库更新了模型并选择了

之间的距离

 <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>

我做了一个局部课并编写了这个方法

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

我多次尝试使用此代码查询函数，但是出现错误

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

当我尝试count或foreach NParcel时，我收到此错误

指定的方法'Double DistanceBetween（Double，Double，Double，无法翻译类型'EFSample.GeoDataEntities'上的'））进入LINQ to Entities存储表达式。

和stacktrace

在 System.Data.Objects.ELinq.ExpressionConverter.ThrowUnresolvableFunction（表达式表达式） System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.FunctionCallTranslator.TranslateFunctionCall（ExpressionConverter parent，MethodCallExpression调用，EdmFunctionAttribute functionAttribute）at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate（ExpressionConverter parent，MethodCallExpression linq）at System.Data.Objects.ELinq.ExpressionConverter.BinaryTranslator.TypedTranslate（ExpressionConverter parent，BinaryExpression linq）at System.Data.Objects.ELinq.ExpressionConverter.TranslateExpression（表达式 linq）at System.Data.Objects.ELinq.ExpressionConverter.TranslateLambda（LambdaExpression lambda，DbExpression输入）at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate（ExpressionConverter parent，MethodCallExpression call，DbExpression＆amp;资源， DbExpressionBinding＆安培; sourceBinding，DbExpression＆amp; lambda） System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate（ExpressionConverter parent，MethodCallExpression call）at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate（ExpressionConverter parent，MethodCallExpression linq）at System.Data.Objects.ELinq.ExpressionConverter.TranslateExpression（表达式 linq）at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.AggregateTranslator.Translate（ExpressionConverter parent，MethodCallExpression call）at System.Data.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate（ExpressionConverter parent，MethodCallExpression linq）at System.Data.Objects.ELinq.ExpressionConverter.Convert（）at System.Data.Objects.ELinq.ELinqQueryState.GetExecutionPlan（可空1 forMergeOption) at System.Data.Objects.ObjectQuery 1.GetResults（可空1 forMergeOption) at System.Data.Objects.ObjectQuery 1.System.Collections.Generic.IEnumerable.GetEnumerator（）在System.Linq.Enumerable.Single [TSource]（IEnumerable 1 source) at System.Linq.Queryable.Count[TSource](IQueryable 1来源）

Answer 1

以下是您的操作方法：

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>

第2步：导入功能

双击edmx
在“模型浏览器”视图中，展开GeoDataModel.Store（可以命名为其他名称）
展开stored procedures /function
双击DistanceBetween
Scalars = Single
点击确定

第3步：在C＃中：

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

注意 IsComposable="false"而没有ReturnType并且不要忘记添加：

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

希望有帮助....

如何使用带有linq的标量值函数实体？

1 个答案: