在 Entity Framework Core v3.1.4 中使用 Take() LINQ 方法

【问题标题】：Use of Take() LINQ Method in Entity Framework Core v3.1.4在 Entity Framework Core v3.1.4 中使用 Take() LINQ 方法
【发布时间】：2020-09-16 17:46:56
【问题描述】：

我正在尝试在我的 API 请求中添加一个限制 GET 查询参数（即 ?limit=10），然后Take() LINQ 方法将使用此限制的值来仅获取我的结果数想。我想要做的是将 LINQ Take() 方法作为 LINQ-TO-T-SQL 查询的一部分包含在内，并将限制作为 SQL 查询的一部分执行。我尝试了以下代码。我还捕获了错误堆栈跟踪。

代码 1：对于此代码，我尝试在查询中的顶级资源上使用 Take()。然后之后（在q 的声明中），我正在执行与顶级资源相关的子查询。

baseQuery = baseQuery.Take(2);

var q = from doctor in baseQuery

        let sp = (from ds in db.DoctorSpecialty
                  join s in db.Specialty on ds.SpecialtyID equals s.SpecialtyID
                  where ds.DoctorID == doctor.DoctorID
                  select new
                  {
                      s.SpecialtyID,
                      s.Specialty1
                  }).ToList()

        let clinics = (from c in db.Clinic
                  where c.DoctorID == doctor.DoctorID && c.Active == true

                  let schedule = (from sc in db.Schedule
                                  where sc.ClinicID == c.ClinicID
                                    && sc.DoctorID == doctor.DoctorID
                                    && DoctorDirectoryConstants.ValidScheduleNotes.Contains(sc.Notes)
                                  select sc).ToList()

                  select new
                  {
                      c.ClinicID,
                      c.Street,
                      c.ClinicName,
                      c.ContactNumber,
                      c.City,
                      c.Province,
                      c.HomeNumber,
                      c.MobileNumber,
                      c.WorkNumber,
                      c.Email,
                      Schedules = schedule,
                  }).ToList() 
        select new
        {
            Doctor = doctor,
            Specialties = sp,
            Clinics = clinics

        };

var rs = q.ToList();

代码 1 的错误堆栈跟踪：

fail: Microsoft.EntityFrameworkCore.Database.Command[20102]
      Failed executing DbCommand (5ms) [Parameters=[@__p_0='?' (DbType = Int32)], CommandType='Text', CommandTimeout='30']
      SELECT [t].[DoctorID], [t].[Address], [t].[AvailableInvites], [t].[Birthdate], [t].[City], [t].[CityID], [t].[ContactNumber], [t].[Country], [t].[DateRegistered], [t].[Description], [t].[DoctorUrl], [t].[Email], [t].[EmailActivated], [t].[EmailUID], [t].[EmailVerifiedFirstTime], [t].[Facebook], [t].[FirstName], [t].[Gender], [t].[GooglePlus], [t].[HomeNumber], [t].[Image], [t].[LastName], [t].[LinkedIn], [t].[MainSpecialty], [t].[ManuallyVerified], [t].[MedicalSchool], [t].[MedicalSchoolYear], [t].[MiddleName], [t].[MobileNumber], [t].[Nationality], [t].[OriginalIssueDate], [t].[PRCNumber], [t].[PageOkay], [t].[PatientNumber], [t].[PhicNumber], [t].[PractisingSince], [t].[Province], [t].[PtrNumber], [t].[Residency], [t].[ResidencyYear], [t].[S2Number], [t].[ShowPublicProfile], [t].[Status], [t].[Street], [t].[Suffix], [t].[Title], [t].[Twitter], [t].[UserID], [t].[Website], [t].[WorkNumber], [t].[Zipcode], [t0].[SpecialtyID], [t0].[Specialty], [t0].[Id], [t2].[ClinicID], [t2].[Street], [t2].[ClinicName], [t2].[ContactNumber], [t2].[City], [t2].[Province], [t2].[HomeNumber], [t2].[MobileNumber], [t2].[WorkNumber], [t2].[Email], [t2].[ScheduleID], [t2].[Active], [t2].[ClinicID0], [t2].[DateModified], [t2].[DayOfWeek], [t2].[DoctorID], [t2].[Notes], [t2].[StartFrom], [t2].[TimeEnd], [t2].[TimeStart], [t2].[Until]
      FROM (
          SELECT TOP(@__p_0) [d].[DoctorID], [d].[Address], [d].[AvailableInvites], [d].[Birthdate], [d].[City], [d].[CityID], [d].[ContactNumber], [d].[Country], [d].[DateRegistered], [d].[Description], [d].[DoctorUrl], [d].[Email], [d].[EmailActivated], [d].[EmailUID], [d].[EmailVerifiedFirstTime], [d].[Facebook], [d].[FirstName], [d].[Gender], [d].[GooglePlus], [d].[HomeNumber], [d].[Image], [d].[LastName], [d].[LinkedIn], [d].[MainSpecialty], [d].[ManuallyVerified], [d].[MedicalSchool], [d].[MedicalSchoolYear], [d].[MiddleName], [d].[MobileNumber], [d].[Nationality], [d].[OriginalIssueDate], [d].[PRCNumber], [d].[PageOkay], [d].[PatientNumber], [d].[PhicNumber], [d].[PractisingSince], [d].[Province], [d].[PtrNumber], [d].[Residency], [d].[ResidencyYear], [d].[S2Number], [d].[ShowPublicProfile], [d].[Status], [d].[Street], [d].[Suffix], [d].[Title], [d].[Twitter], [d].[UserID], [d].[Website], [d].[WorkNumber], [d].[Zipcode]
          FROM [Doctor] AS [d]
          WHERE [d].[Status] = 'good'
      ) AS [t]
      LEFT JOIN (
          SELECT [s].[SpecialtyID], [s].[Specialty], [d0].[Id], [d0].[DoctorID]
          FROM [DoctorSpecialty] AS [d0]
          INNER JOIN [Specialty] AS [s] ON [d0].[SpecialtyID] = [s].[SpecialtyID]
      ) AS [t0] ON [t].[DoctorID] = [t0].[DoctorID]
      LEFT JOIN (
          SELECT [c].[ClinicID], [c].[Street], [c].[ClinicName], [c].[ContactNumber], [c].[City], [c].[Province], [c].[HomeNumber], [c].[MobileNumber], [c].[WorkNumber], [c].[Email], [t1].[ScheduleID], [t1].[Active], [t1].[ClinicID] AS [ClinicID0], [t1].[DateModified], [t1].[DayOfWeek], [t1].[DoctorID], [t1].[Notes], [t1].[StartFrom], [t1].[TimeEnd], [t1].[TimeStart], [t1].[Until], [c].[DoctorID] AS [DoctorID0]
          FROM [Clinic] AS [c]
          LEFT JOIN (
              SELECT [s0].[ScheduleID], [s0].[Active], [s0].[ClinicID], [s0].[DateModified], [s0].[DayOfWeek], [s0].[DoctorID], [s0].[Notes], [s0].[StartFrom], [s0].[TimeEnd], [s0].[TimeStart], [s0].[Until]
              FROM [Schedule] AS [s0]
              WHERE ([s0].[DoctorID] = [d].[DoctorID]) AND [s0].[Notes] IN (N'Walk-In', N'By Appointment')
          ) AS [t1] ON [c].[ClinicID] = [t1].[ClinicID]
          WHERE [c].[Active] = CAST(1 AS bit)
      ) AS [t2] ON [t].[DoctorID] = [t2].[DoctorID0]
      ORDER BY [t].[DoctorID], [t0].[Id], [t0].[SpecialtyID], [t2].[ClinicID], [t2].[ScheduleID]
fail: Microsoft.EntityFrameworkCore.Query[10100]
      An exception occurred while iterating over the results of a query for context type 'SeriousMDCommonsCore.Models.Database.SeriousmdEntitiesContext'.
      Microsoft.Data.SqlClient.SqlException (0x80131904): The multi-part identifier "d.DoctorID" could not be bound.
         at Microsoft.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
         at Microsoft.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
         at Microsoft.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose)
         at Microsoft.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady)
         at Microsoft.Data.SqlClient.SqlDataReader.TryConsumeMetaData()
         at Microsoft.Data.SqlClient.SqlDataReader.get_MetaData()
         at Microsoft.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString, Boolean isInternal, Boolean forDescribeParameterEncryption, Boolean shouldCacheForAlwaysEncrypted)
         at Microsoft.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean isAsync, Int32 timeout, Task& task, Boolean asyncWrite, Boolean inRetry, SqlDataReader ds, Boolean describeParameterEncryptionRequest)
         at Microsoft.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean& usedCache, Boolean asyncWrite, Boolean inRetry, String method)
         at Microsoft.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)
         at Microsoft.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior)
         at Microsoft.Data.SqlClient.SqlCommand.ExecuteDbDataReader(CommandBehavior behavior)
         at System.Data.Common.DbCommand.ExecuteReader()
         at Microsoft.EntityFrameworkCore.Storage.RelationalCommand.ExecuteReader(RelationalCommandParameterObject parameterObject)
         at Microsoft.EntityFrameworkCore.Query.Internal.QueryingEnumerable`1.Enumerator.InitializeReader(DbContext _, Boolean result)
         at Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal.SqlServerExecutionStrategy.Execute[TState,TResult](TState state, Func`3 operation, Func`3 verifySucceeded)
         at Microsoft.EntityFrameworkCore.Query.Internal.QueryingEnumerable`1.Enumerator.MoveNext()
      ClientConnectionId:0b10b611-bd0f-4fcb-a543-fdbe530fc029
      Error Number:4104,State:1,Class:16
Microsoft.Data.SqlClient.SqlException (0x80131904): The multi-part identifier "d.DoctorID" could not be bound.
   at Microsoft.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
   at Microsoft.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
   at Microsoft.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose)
   at Microsoft.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady)
   at Microsoft.Data.SqlClient.SqlDataReader.TryConsumeMetaData()
   at Microsoft.Data.SqlClient.SqlDataReader.get_MetaData()
   at Microsoft.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString, Boolean isInternal, Boolean forDescribeParameterEncryption, Boolean shouldCacheForAlwaysEncrypted)
   at Microsoft.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean isAsync, Int32 timeout, Task& task, Boolean asyncWrite, Boolean inRetry, SqlDataReader ds, Boolean describeParameterEncryptionRequest)
   at Microsoft.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean& usedCache, Boolean asyncWrite, Boolean inRetry, String method)
   at Microsoft.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)
   at Microsoft.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior)
   at Microsoft.Data.SqlClient.SqlCommand.ExecuteDbDataReader(CommandBehavior behavior)
   at System.Data.Common.DbCommand.ExecuteReader()
   at Microsoft.EntityFrameworkCore.Storage.RelationalCommand.ExecuteReader(RelationalCommandParameterObject parameterObject)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryingEnumerable`1.Enumerator.InitializeReader(DbContext _, Boolean result)
   at Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal.SqlServerExecutionStrategy.Execute[TState,TResult](TState state, Func`3 operation, Func`3 verifySucceeded)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryingEnumerable`1.Enumerator.MoveNext()
ClientConnectionId:0b10b611-bd0f-4fcb-a543-fdbe530fc029
Error Number:4104,State:1,Class:16
fail: Microsoft.AspNetCore.Server.Kestrel[13]
      Connection id "0HM03JVLBFS8O", Request id "0HM03JVLBFS8O:00000001": An unhandled exception was thrown by the application.
Microsoft.Data.SqlClient.SqlException (0x80131904): The multi-part identifier "d.DoctorID" could not be bound.
   at Microsoft.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
   at Microsoft.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
   at Microsoft.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose)
   at Microsoft.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady)
   at Microsoft.Data.SqlClient.SqlDataReader.TryConsumeMetaData()
   at Microsoft.Data.SqlClient.SqlDataReader.get_MetaData()
   at Microsoft.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString, Boolean isInternal, Boolean forDescribeParameterEncryption, Boolean shouldCacheForAlwaysEncrypted)
   at Microsoft.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean isAsync, Int32 timeout, Task& task, Boolean asyncWrite, Boolean inRetry, SqlDataReader ds, Boolean describeParameterEncryptionRequest)
   at Microsoft.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean& usedCache, Boolean asyncWrite, Boolean inRetry, String method)
   at Microsoft.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)
   at Microsoft.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior)
   at Microsoft.Data.SqlClient.SqlCommand.ExecuteDbDataReader(CommandBehavior behavior)
   at System.Data.Common.DbCommand.ExecuteReader()
   at Microsoft.EntityFrameworkCore.Storage.RelationalCommand.ExecuteReader(RelationalCommandParameterObject parameterObject)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryingEnumerable`1.Enumerator.InitializeReader(DbContext _, Boolean result)
   at Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal.SqlServerExecutionStrategy.Execute[TState,TResult](TState state, Func`3 operation, Func`3 verifySucceeded)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryingEnumerable`1.Enumerator.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at lambda_method(Closure , Object , Object[] )
   at Microsoft.Extensions.Internal.ObjectMethodExecutor.Execute(Object target, Object[] parameters)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.SyncObjectResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeActionMethodAsync()
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeNextActionFilterAsync()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.ProcessRequests[TContext](IHttpApplication`1 application)
ClientConnectionId:0b10b611-bd0f-4fcb-a543-fdbe530fc029
Error Number:4104,State:1,Class:16

代码 2：在这里，我不是在 baseQuery 中执行 Take()，而是在最终查询表达式 q 中执行 Take()。我还添加了doctor.DoctorID 作为某种id，我认为需要将其提供给Take() LINQ 方法

var q = from doctor in baseQuery

        let sp = (from ds in db.DoctorSpecialty
                  join s in db.Specialty on ds.SpecialtyID equals s.SpecialtyID
                  where ds.DoctorID == doctor.DoctorID
                  select new
                  {
                      s.SpecialtyID,
                      s.Specialty1
                  }).ToList()

        let clinics = (from c in db.Clinic
                  where c.DoctorID == doctor.DoctorID && c.Active == true

                  let schedule = (from sc in db.Schedule
                                  where sc.ClinicID == c.ClinicID
                                    && sc.DoctorID == doctor.DoctorID
                                    && DoctorDirectoryConstants.ValidScheduleNotes.Contains(sc.Notes)
                                  select sc).ToList()

                  select new
                  {
                      c.ClinicID,
                      c.Street,
                      c.ClinicName,
                      c.ContactNumber,
                      c.City,
                      c.Province,
                      c.HomeNumber,
                      c.MobileNumber,
                      c.WorkNumber,
                      c.Email,
                      Schedules = schedule,
                  }).ToList() 
        select new
        {
            doctor.DoctorID,
            Doctor = doctor,
            Specialties = sp,
            Clinics = clinics

        };

q = q.Take(2);

var rs = q.ToList();

代码 2 的错误堆栈跟踪：这里的错误与代码 2 的错误有所不同，似乎Take() LINQ 方法正在使用添加的索引，但仍然抛出错误。

fail: Microsoft.AspNetCore.Server.Kestrel[13]
      Connection id "0HM03K296O68T", Request id "0HM03K296O68T:00000001": An unhandled exception was thrown by the application.
System.InvalidOperationException: Processing of the LINQ expression '(ProjectionBindingExpression: 0)' by 'RelationalProjectionBindingExpressionVisitor' failed. This may indicate either a bug or a limitation in EF Core. See https://go.microsoft.com/fwlink/?linkid=2101433 for more detailed information.
   at Microsoft.EntityFrameworkCore.Query.Internal.RelationalProjectionBindingExpressionVisitor.VisitExtension(Expression extensionExpression)
   at System.Linq.Expressions.Expression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.Internal.RelationalProjectionBindingExpressionVisitor.Visit(Expression expression)
   at Microsoft.EntityFrameworkCore.Query.Internal.RelationalProjectionBindingExpressionVisitor.VisitNew(NewExpression newExpression)
   at System.Linq.Expressions.NewExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.Internal.RelationalProjectionBindingExpressionVisitor.Visit(Expression expression)
   at Microsoft.EntityFrameworkCore.Query.Internal.RelationalProjectionBindingExpressionVisitor.Translate(SelectExpression selectExpression, Expression expression)
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryableMethodTranslatingExpressionVisitor.TranslateSelect(ShapedQueryExpression source, LambdaExpression selector)
   at Microsoft.EntityFrameworkCore.Query.QueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.QueryCompilationContext.CreateQueryExecutor[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery[TResult](Expression query, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore[TResult](IDatabase database, Expression query, IModel model, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass9_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQueryCore[TFunc](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQuery[TResult](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1.GetEnumerator()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at lambda_method(Closure , Object , Object[] )
   at Microsoft.Extensions.Internal.ObjectMethodExecutor.Execute(Object target, Object[] parameters)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.SyncObjectResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeActionMethodAsync()
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeNextActionFilterAsync()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.ProcessRequests[TContext](IHttpApplication`1 application)

回到我的问题，如何将Take() LINQ 方法集成为我的 LINQ-TO-T-SQL 查询的一部分，以便我的所有查询都将通过 EF Core，并且所有查询操作都将在数据库中执行?

【问题讨论】：

  • 您使用的是哪个版本的 EF 内核？
  • @GuruStron 我正在使用 EF Core v3.1.4
  • 通常当你有 let 时，ToList() 这些就像 sql 中的 cte's/temp 表，所以把它分开以便更容易理解，也就是我要做的就是写我的 sql希望它生成然后将其转换为linq。当您想要做的事情不是直截了当时，它会更容易，因为您更好地了解工具的局限性。你可以在 sql 中做的任何事情都可以在 linq 中做。所以在sql中进行查询，然后它将帮助如何在linq中进行查询。
  • 我的意思是只要你ToList() 在你执行它的任何部分。但有时必须这样做……比如 CTE/Temp 表。

标签： c# asp.net-mvc linq asp.net-core entity-framework-core


【解决方案1】：

在第一个查询中尝试更改doctor.DoctorID in：

let schedule = (from sc in db.Schedule
                where sc.ClinicID == c.ClinicID
                && sc.DoctorID == doctor.DoctorID
                && DoctorDirectoryConstants.ValidScheduleNotes.Contains(sc.Notes)
                select sc)

致c.DoctorID:

let schedule = (from sc in db.Schedule
                where sc.ClinicID == c.ClinicID
                && sc.DoctorID == c.DoctorID
                && DoctorDirectoryConstants.ValidScheduleNotes.Contains(sc.Notes)
                select sc)

UPD

如果您浏览 SQL，您将看到为时间表生成的代码：

LEFT JOIN (
              SELECT [s0].[ScheduleID], [s0].[Active], [s0].[ClinicID], [s0].[DateModified], [s0].[DayOfWeek], [s0].[DoctorID], [s0].[Notes], [s0].[StartFrom], [s0].[TimeEnd], [s0].[TimeStart], [s0].[Until]
              FROM [Schedule] AS [s0]
              WHERE ([s0].[DoctorID] = [d].[DoctorID]) AND [s0].[Notes] IN (N'Walk-In', N'By Appointment')
          ) AS [t1] ON [c].[ClinicID] = [t1].[ClinicID]

查看它具有 WHERE ([s0].[DoctorID] = [d].[DoctorID]) 条件的 where 子句，该条件引用了无法访问的 [d].[DoctorID]，因为它只能在执行 Take 的根子选择中访问。似乎 EF Core 中存在一个令人费解的错误。

【讨论】：

  • 嗨@GuruStron，它现在适用于代码 1。非常感谢！你能解释一下它工作的原因吗？
【解决方案2】：

代码 3：此版本的代码通过Take() LINQ 方法成功返回了我想要的结果数。但是，Take() 正在对已加载到客户端或内存中的数据/集合执行。所以这个 Take() 执行 LINQ-TO-Collections 查询而不是 LINQ-TO-T-SQL 并且不通过 EF Core。

var q = from doctor in baseQuery

        let sp = (from ds in db.DoctorSpecialty
                  join s in db.Specialty on ds.SpecialtyID equals s.SpecialtyID
                  where ds.DoctorID == doctor.DoctorID
                  select new
                  {
                      s.SpecialtyID,
                      s.Specialty1
                  }).ToList()

        let clinics = (from c in db.Clinic
                  where c.DoctorID == doctor.DoctorID && c.Active == true

                  let schedule = (from sc in db.Schedule
                                  where sc.ClinicID == c.ClinicID
                                    && sc.DoctorID == doctor.DoctorID
                                    && DoctorDirectoryConstants.ValidScheduleNotes.Contains(sc.Notes)
                                  select sc).ToList()

                  select new
                  {
                      c.ClinicID,
                      c.Street,
                      c.ClinicName,
                      c.ContactNumber,
                      c.City,
                      c.Province,
                      c.HomeNumber,
                      c.MobileNumber,
                      c.WorkNumber,
                      c.Email,
                      Schedules = schedule,
                  }).ToList() 
        select new
        {
            Doctor = doctor,
            Specialties = sp,
            Clinics = clinics

        };

var rs = q.ToList();

rs = rs.AsEnumerable().Take(2).ToList();

【讨论】：

  • 仅供参考，您不需要 AsEnumerable() in rs = rs.AsEnumerable().Take(2).ToList()
  • 您好@GuruStron 指出。谢谢！我试过了，它可以工作rs = rs.Take(2).ToList();
猜你喜欢
  • 2021-02-27
  • 1970-01-01
  • 2019-06-27
  • 2021-07-20
  • 2022-08-20
  • 2017-04-25
  • 2020-05-17
  • 2020-08-27
  • 1970-01-01
相关资源
最近更新 更多
热门标签
Java Python linux javascript Mysql C# Docker 算法 前端 SpringBoot Redis Vue spring 设计模式 .net core .net kubernetes c++ 数据库 数据结构 大数据 js 机器学习 微服务 Android Go 程序员 面试 JVM ASP.net core 云原生 人工智能 后端 PHP git CSS golang k8s Nginx Django mybatis 深度学习 多线程 React 架构 devops 爬虫 云计算 Spring Boot LeetCode