LINQ左外连接查询错误：OuterApply没有相应的密钥
我正在使用Entity Framework作为我的ORM连接两个SQL函数。 当查询执行时，我收到以下错误消息：
The query attempted to call 'Outer Apply' over a nested query, but 'OuterApply' did not have the appropriate keys 这是我的查询：
var ingredientAllergenData = (from ings in db.fnListIngredientsFromItem(productId, (short)itemType, productId) join ingAllergens in db.fnListAllergensFromItems(productId.ToString(CultureInfo.InvariantCulture), (short)itemType, currentLang) on ings.id equals ingAllergens.ingredientId into ingAllergensData from allergens in ingAllergensData.DefaultIfEmpty() where ings.table == "tblIng" || ings.table == "" select new {ings, allergens}).ToList();
我在LINQPad中写了相同的查询，我得到了结果，所以我不确定是什么问题：
var ingredientAllergenData = (from ings in fnListIngredientsFromItem(1232, 0, 1232) join ingAllergens in fnListAllergensFromItems("1232", 0, 1) on ings.Id equals ingAllergens.IngredientId into ingAllergensData from allergens in ingAllergensData.DefaultIfEmpty() where ings.Table == "tblIng" || ings.Table == "" select new {ings, allergens}).ToList();
来自linqpad的回复： 
编辑这是LINQPad中生成的SQL查询：
-- Region Parameters DECLARE @p0 Int = 1232 DECLARE @p1 Int = 0 DECLARE @p2 Int = 1232 DECLARE @p3 VarChar(1000) = '1232' DECLARE @p4 SmallInt = 0 DECLARE @p5 Int = 1 DECLARE @p6 VarChar(1000) = 'tblIng' DECLARE @p7 VarChar(1000) = '' -- EndRegion SELECT [t0].[prodId] AS [ProdId], [t0].[id] AS [Id], [t0].[parent] AS [Parent], [t0].[name] AS [Name], [t0].[ing_gtin] AS [Ing_gtin], [t0].[ing_artsup] AS [Ing_artsup], [t0].[table] AS [Table], [t0].[quantity] AS [Quantity], [t2].[test], [t2].[prodId] AS [ProdId2], [t2].[ingredientId] AS [IngredientId], [t2].[allergenId] AS [AllergenId], [t2].[allergenName] AS [AllergenName], [t2].[level_of_containment] AS [Level_of_containment] FROM [dbo].[fnListIngredientsFromItem](@p0, @p1, @p2) AS [t0] LEFT OUTER JOIN ( SELECT 1 AS [test], [t1].[prodId], [t1].[ingredientId], [t1].[allergenId], [t1].[allergenName], [t1].[level_of_containment] FROM [dbo].[fnListAllergensFromItems](@p3, @p4, @p5) AS [t1] ) AS [t2] ON [t0].[id] = ([t2].[ingredientId]) WHERE ([t0].[table] = @p6) OR ([t0].[table] = @p7)
我也尝试将相同的数字硬编码到C＃中，并再次得到相同的错误。
问题是entity framework需要知道TVF结果的主键列是做什么左连接，而默认生成的EDMX文件不包含该信息。 您可以通过将TVF结果映射到实体来添加键值信息（而不是映射到复杂类型的默认值）。
在LINQPad中相同查询的原因是，用于连接LINQPad中的数据库的默认数据上下文驱动程序使用LINQ to SQL（而不是entity framework）。 但我能够让查询在Entity Framework中运行（最终）。
我设置了一个类似表值函数的本地SQL Server数据库：
CREATE FUNCTION fnListIngredientsFromItem(@prodId int, @itemType1 smallint, @parent int) RETURNS TABLE AS RETURN ( select prodId = 1232, id = 1827, parent = 1232, name = 'Ossenhaaspunten', ing_gtin = 3003210089821, ing_artsup=141020, [table] = 'tblIng', quantity = '2 K' ); go CREATE FUNCTION fnListAllergensFromItems(@prodIdString varchar(1000), @itemType2 smallint, @lang int) RETURNS TABLE AS RETURN ( select prodId = '1232', ingredientId = 1827, allergenId = 11, allergenName = 'fish', level_of_containment = 2 union all select prodId = '1232', ingredientId = 1827, allergenId = 16, allergenName = 'tree nuts', level_of_containment = 2 union all select prodId = '1232', ingredientId = 1827, allergenId = 12, allergenName = 'crustacean and shellfish', level_of_containment = 2 ); go
我使用Entity Framework 6.1.2创建了一个测试项目，并使用Visual Studio 2013中的实体数据模型设计器从数据库生成了一个EDMX文件。通过此设置，我在尝试运行该查询时遇到了同样的错误：
System.NotSupportedException HResult=-2146233067 Message=The query attempted to call 'OuterApply' over a nested query, but 'OuterApply' did not have the appropriate keys. Source=EntityFramework StackTrace: at System.Data.Entity.Core.Query.PlanCompiler.NestPullup.ApplyOpJoinOp(Op op, Node n) at System.Data.Entity.Core.Query.PlanCompiler.NestPullup.VisitApplyOp(ApplyBaseOp op, Node n) at System.Data.Entity.Core.Query.InternalTrees.BasicOpVisitorOfT`1.Visit(OuterApplyOp op, Node n) ...
为左连接运行备用表达式会导致稍有不同的错误：
var ingredientAllergenData = (db.fnListIngredientsFromItem(1323, (short)0, 1) .GroupJoin(db.fnListAllergensFromItems("1232", 0, 1), ing => ing.id, allergen => allergen.ingredientId, (ing, allergen) => new { ing, allergen } ) ).ToList();
这是来自新exception的截断堆栈跟踪：
System.NotSupportedException HResult=-2146233067 Message=The nested query does not have the appropriate keys. Source=EntityFramework StackTrace: at System.Data.Entity.Core.Query.PlanCompiler.NestPullup.ConvertToSingleStreamNest(Node nestNode, Dictionary`2 varRefReplacementMap, VarList flattenedOutputVarList, SimpleColumnMap[]& parentKeyColumnMaps) at System.Data.Entity.Core.Query.PlanCompiler.NestPullup.Visit(PhysicalProjectOp op, Node n) at System.Data.Entity.Core.Query.InternalTrees.PhysicalProjectOp.Accept[TResultType](BasicOpVisitorOfT`1 v, Node n) ...
entity framework是开源的，因此我们实际上可以查看引发此exception的源代码。 此代码段中的注释解释了问题所在（ https://entityframework.codeplex.com/SourceControl/latest#src/EntityFramework/Core/Query/PlanCompiler/NestPullup.cs ）：
// Make sure that the driving node has keys defined. Otherwise we're in // trouble; we must be able to infer keys from the driving node. var drivingNode = nestNode.Child0; var drivingNodeKeys = Command.PullupKeys(drivingNode); if (drivingNodeKeys.NoKeys) { // ALMINEEV: In this case we used to wrap drivingNode into a projection that would also project Edm.NewGuid() thus giving us a synthetic key. // This solution did not work however due to a bug in SQL Server that allowed pulling non-deterministic functions above joins and applies, thus // producing incorrect results. SQL Server bug was filed in "sqlbuvsts01\Sql Server" database as #725272. // The only known path how we can get a keyless drivingNode is if // - drivingNode is over a TVF call // - TVF is declared as Collection(Row) is SSDL (the only form of TVF definitions at the moment) // - TVF is not mapped to entities // Note that if TVF is mapped to entities via function import mapping, and the user query is actually the call of the // function import, we infer keys for the TVF from the c-space entity keys and their mappings. throw new NotSupportedException(Strings.ADP_KeysRequiredForNesting); }
这解释了导致该错误的路径，因此我们可以做的任何事情都可以解决问题。 假设我们必须在表值函数的结果上进行左连接，一个选项（可能是唯一的选项？）是将TVF的结果映射到具有主键的实体。 然后，entity framework将根据到该实体的映射知道TVF结果的关键值，并且我们应该避免与丢失密钥相关的这些错误。
默认情况下，从数据库生成EDMX文件时，TVF将映射到复杂类型。 有关如何更改它的说明， 请访问https://msdn.microsoft.com/en-us/library/vstudio/ee534438%28v=vs.100%29.aspx 。
在我的测试项目中，我添加了一个空表，其模式与TVF的输出相匹配，以使模型设计者生成实体，然后我进入模型浏览器并更新函数导入以返回这些实体的集合（而不是自动生成的复杂类型）。 进行这些更改后，同样的LINQ查询运行没有错误。
var ingredientAllergenData = (from ings in db.fnListIngredientsFromItem(productId, (short)itemType, productId) join ingAllergens in db.fnListAllergensFromItems(productId.ToString(CultureInfo.InvariantCulture), (short)itemType, currentLang) on ings.id equals ingAllergens.ingredientId into ingAllergensData from allergens in ingAllergensData.DefaultIfEmpty() where ings.table == "tblIng" || ings.table == "" select new {ings, allergens}).ToList();
这是查询给我的跟踪SQL：
SELECT 1 AS [C1], [Extent1].[prodId] AS [prodId], [Extent1].[id] AS [id], [Extent1].[parent] AS [parent], [Extent1].[name] AS [name], [Extent1].[ing_gtin] AS [ing_gtin], [Extent1].[ing_artsup] AS [ing_artsup], [Extent1].[table] AS [table], [Extent1].[quantity] AS [quantity], [Extent2].[prodId] AS [prodId1], [Extent2].[ingredientId] AS [ingredientId], [Extent2].[allergenId] AS [allergenId], [Extent2].[allergenName] AS [allergenName], [Extent2].[level_of_containment] AS [level_of_containment] FROM [dbo].[fnListIngredientsFromItem](@prodId, @itemType1, @parent) AS [Extent1] LEFT OUTER JOIN [dbo].[fnListAllergensFromItems](@prodIdString, @itemType2, @lang) AS [Extent2] ON ([Extent1].[id] = [Extent2].[ingredientId]) OR (([Extent1].[id] IS NULL) AND ([Extent2].[ingredientId] IS NULL)) WHERE [Extent1].[table] IN ('tblIng','')