在EF 4.0中将String转换为Int

Question

有没有办法做到这一点?我在DB中有一个字符串字段，我想在我的LINQ查询中将其解析为int属性(是的，它必须在IQueryable级别，而不是在内存中)。

我知道两年前的EF 1.0做不到这一点(即使LINQ to SQL支持这个基本功能)…但我只是想知道是否有人提出了一种方法来做到这一点?

自定义函数映射?特殊的语法吗?任何东西....

更新:

我尝试了一个模型定义的函数，如下所示:

    <Function Name="ConvertToInt32" ReturnType="Edm.Int32">
      <Parameter Name="v" Type="Edm.String" />
      <DefiningExpression>
        CAST(v AS INT)
      </DefiningExpression>
    </Function>
    [EdmFunction("Model.Repository", "ConvertToInt32")]
    public static int ConvertToInt32(string value)
    {
        throw new InvalidOperationException("Only valid when used as part of a LINQ query.");
    }

但它似乎不起作用。我得到运行时异常:

        ErrorDescription=Type 'INT' could not be found. Make sure that the required schemas are loaded and that the namespaces are imported correctly.
        StackTrace:
             at System.Data.Common.EntitySql.SemanticAnalyzer.ConvertTypeName(Node typeName, SemanticResolver sr)
             at System.Data.Common.EntitySql.SemanticAnalyzer.ConvertTypeExprArgs(BuiltInExpr astBuiltInExpr, SemanticResolver sr)
             at System.Data.Common.EntitySql.SemanticAnalyzer.<CreateBuiltInExprConverter>b__73(BuiltInExpr bltInExpr, SemanticResolver sr)
             at System.Data.Common.EntitySql.SemanticAnalyzer.ConvertBuiltIn(Node astExpr, SemanticResolver sr)
             at System.Data.Common.EntitySql.SemanticAnalyzer.Convert(Node astExpr, SemanticResolver sr)
             at System.Data.Common.EntitySql.SemanticAnalyzer.ConvertValueExpression(Node astExpr, SemanticResolver sr)
             at System.Data.Common.EntitySql.SemanticAnalyzer.ConvertQueryStatementToDbExpression(Statement astStatement, SemanticResolver sr)
             at System.Data.Common.EntitySql.SemanticAnalyzer.AnalyzeQueryCommand(Node astExpr)
             at System.Data.Common.EntitySql.CqlQuery.<AnalyzeQueryExpressionSemantics>b__8(SemanticAnalyzer analyzer, Node astExpr)
             at System.Data.Common.EntitySql.CqlQuery.AnalyzeSemanticsCommon[TResult](Node astExpr, Perspective perspective, ParserOptions parserOptions, IEnumerable`1 parameters, IEnumerable`1 variables, Func`3 analysisFunction)
             at System.Data.Common.EntitySql.CqlQuery.AnalyzeQueryExpressionSemantics(Node astQueryCommand, Perspective perspective, ParserOptions parserOptions, IEnumerable`1 parameters, IEnumerable`1 variables)
             at System.Data.Common.EntitySql.CqlQuery.<>c__DisplayClass4.<CompileQueryCommandLambda>b__3(Node astCommand, ParserOptions validatedParserOptions)
             at System.Data.Common.EntitySql.CqlQuery.CompileCommon[TResult](String commandText, Perspective perspective, ParserOptions parserOptions, Func`3 compilationFunction)
             at System.Data.Common.EntitySql.CqlQuery.CompileQueryCommandLambda(String queryCommandText, Perspective perspective, ParserOptions parserOptions, IEnumerable`1 parameters, IEnumerable`1 variables)
             at System.Data.Mapping.ViewGeneration.Utils.ExternalCalls.CompileFunctionDefinition(String functionFullName, String functionDefinition, IList`1 functionParameters, EdmItemCollection edmItemCollection)
             at System.Data.Metadata.Edm.EdmItemCollection.GenerateFunctionDefinition(EdmFunction function)
             at System.Data.Common.Utils.Memoizer`2.<>c__DisplayClass2.<Evaluate>b__0()
             at System.Data.Common.Utils.Memoizer`2.Result.GetValue()
             at System.Data.Common.Utils.Memoizer`2.Evaluate(TArg arg)
             at System.Data.Metadata.Edm.EdmItemCollection.GetGeneratedFunctionDefinition(EdmFunction function)
             at System.Data.Metadata.Edm.MetadataWorkspace.GetGeneratedFunctionDefinition(EdmFunction function)
             at System.Data.Query.PlanCompiler.ITreeGenerator.Visit(DbFunctionExpression e)
        InnerException: 

更新:我让它工作如下

 <Function Name="ConvertToInt32" ReturnType="Edm.Int32">
      <Parameter Name="v" Type="Edm.String" />
      <DefiningExpression>
        CAST(v AS Edm.Int32)
      </DefiningExpression>
    </Function>

Answer 1

如果您正在使用EFv4 + EDMX，您可以创建自定义模型定义的函数，它将为您执行CAST。然后您可以在Linq-to-entities查询中使用该函数。