第二个异步操作开始了......不知道如何
Second async operation started...don't see how
我收到有关在上一个异步操作结束之前在上下文中开始的第二个异步操作的错误，但我看不到它发生的位置。这是我正在使用的代码。每个异步调用都在使用 await，那么我做错了什么？
这是 Web 上的方法 API 2 次调用。
public async Task<IHttpActionResult> SendAssessmentArsAsync(int assessmentId) {
using (var context = new LAMPEntities()) {
var assessment = await context.EHS_Assessment_Audit.AsNoTracking().Where(x => x.id == assessmentId).FirstOrDefaultAsync();
var arsQuery = from r in context.EHS_Assessment_Audit_AR.AsNoTracking()
where r.EHS_Assessment_Audit_Id == assessmentId
join w in context.Worker on r.Assignee_WWID equals w.WWID
select new {
w.Email,
w.Full_Name,
r.AR,
r.Due_Date
};
var ars = await arsQuery.ToArrayAsync();
var lab = from s in context.Lab_Space.AsNoTracking()
where s.id == assessment.Lab_Space.id
join w in context.Worker.AsNoTracking() on s.Contact_WWID equals w.WWID
where w.Email != null
join d_join in context.Worker.AsNoTracking() on s.Delegate equals d_join.WWID into d_grp
from d in d_grp.DefaultIfEmpty()
select new {
Owner = w.Email,
Delegate = d.Email,
Barcode = s.Entry_Bar_Code,
Label = s.Floor_Space_Label,
Id = s.id
};
var mails = await lab.FirstAsync();
当它到达最后一行时，它就会抛出异常。
异常消息：
A second operation started on this context before a previous asynchronous operation completed. Use 'await' to ensure that any asynchronous operations have completed before calling another method on this context. Any instance members are not guaranteed to be thread safe.
这是通过网络服务调用显示的异常：
b__a()
at System.Data.Entity.Core.Objects.ObjectContext.d__3d`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.d__9`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Data.Entity.Utilities.TaskExtensions.CultureAwaiter`1.GetResult()
at System.Data.Entity.Core.Objects.ObjectQuery`1.d__e.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Data.Entity.Utilities.TaskExtensions.CultureAwaiter`1.GetResult()
at System.Data.Entity.Internal.LazyAsyncEnumerator`1.d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Data.Entity.Infrastructure.IDbAsyncEnumerableExtensions.d__1d`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
at LabSORService.Controllers.EHSController.d__21.MoveNext() in ...\Controllers\EHSController.cs:line 854
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Threading.Tasks.TaskHelpersExtensions.d__1`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Web.Http.Controllers.ApiControllerActionInvoker.d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Web.Http.Controllers.ActionFilterResult.d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Web.Http.Dispatcher.HttpControllerDispatcher.d__15.MoveNext()" }
{
"message": "An error has occurred.",
"exceptionMessage": "A second operation started on this context before a previous asynchronous operation completed. Use 'await' to ensure that any asynchronous operations have completed before calling another method on this context. Any instance members are not guaranteed to be thread safe.",
"exceptionType": "System.NotSupportedException",
"stackTrace": " at System.Data.Entity.Core.Objects.ELinq.QueryParameterExpression.TryGetFieldOrPropertyValue(MemberExpression me, Object instance, Object& memberValue)
at System.Data.Entity.Core.Objects.ELinq.QueryParameterExpression.TryEvaluatePath(Expression expression, ConstantExpression& constantExpression)
at System.Data.Entity.Core.Objects.ELinq.QueryParameterExpression.EvaluateParameter(Object[] arguments)
at System.Data.Entity.Core.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable`1 forMergeOption)
at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClassc.
很有可能
where s.id == assessment.Lab_Space.id
在不适当的时间触发 Lab_Space 导航 属性 的延迟加载。
假设你没有像 Lab_Space_Id 这样的显式 FK 属性（如果你有，只需使用它而不是 Lab_Space.id），或者预先加载它（最好）：
var assessment = await context.EHS_Assessment_Audit.AsNoTracking()
.Include(x => x.Lab_Space) // <--
.Where(x => x.id == assessmentId).FirstOrDefaultAsync();
或在查询外对其求值：
var labSpaceId = assessment.Lab_Space.id; // <--
var lab = from s in context.Lab_Space.AsNoTracking()
where s.id == labSpaceId // <--
...
请注意，在原始查询中，assessment.Lab_Space 访问只是 记录在查询表达式树中 。实际评估（因此触发延迟加载）作为查询执行的一部分发生。
我收到有关在上一个异步操作结束之前在上下文中开始的第二个异步操作的错误，但我看不到它发生的位置。这是我正在使用的代码。每个异步调用都在使用 await，那么我做错了什么？
这是 Web 上的方法 API 2 次调用。
public async Task<IHttpActionResult> SendAssessmentArsAsync(int assessmentId) {
using (var context = new LAMPEntities()) {
var assessment = await context.EHS_Assessment_Audit.AsNoTracking().Where(x => x.id == assessmentId).FirstOrDefaultAsync();
var arsQuery = from r in context.EHS_Assessment_Audit_AR.AsNoTracking()
where r.EHS_Assessment_Audit_Id == assessmentId
join w in context.Worker on r.Assignee_WWID equals w.WWID
select new {
w.Email,
w.Full_Name,
r.AR,
r.Due_Date
};
var ars = await arsQuery.ToArrayAsync();
var lab = from s in context.Lab_Space.AsNoTracking()
where s.id == assessment.Lab_Space.id
join w in context.Worker.AsNoTracking() on s.Contact_WWID equals w.WWID
where w.Email != null
join d_join in context.Worker.AsNoTracking() on s.Delegate equals d_join.WWID into d_grp
from d in d_grp.DefaultIfEmpty()
select new {
Owner = w.Email,
Delegate = d.Email,
Barcode = s.Entry_Bar_Code,
Label = s.Floor_Space_Label,
Id = s.id
};
var mails = await lab.FirstAsync();
当它到达最后一行时，它就会抛出异常。
异常消息：
A second operation started on this context before a previous asynchronous operation completed. Use 'await' to ensure that any asynchronous operations have completed before calling another method on this context. Any instance members are not guaranteed to be thread safe.
这是通过网络服务调用显示的异常：
b__a()
at System.Data.Entity.Core.Objects.ObjectContext.d__3d`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.d__9`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Data.Entity.Utilities.TaskExtensions.CultureAwaiter`1.GetResult()
at System.Data.Entity.Core.Objects.ObjectQuery`1.d__e.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Data.Entity.Utilities.TaskExtensions.CultureAwaiter`1.GetResult()
at System.Data.Entity.Internal.LazyAsyncEnumerator`1.d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Data.Entity.Infrastructure.IDbAsyncEnumerableExtensions.d__1d`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
at LabSORService.Controllers.EHSController.d__21.MoveNext() in ...\Controllers\EHSController.cs:line 854
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Threading.Tasks.TaskHelpersExtensions.d__1`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Web.Http.Controllers.ApiControllerActionInvoker.d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Web.Http.Controllers.ActionFilterResult.d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Web.Http.Dispatcher.HttpControllerDispatcher.d__15.MoveNext()" }
{
"message": "An error has occurred.",
"exceptionMessage": "A second operation started on this context before a previous asynchronous operation completed. Use 'await' to ensure that any asynchronous operations have completed before calling another method on this context. Any instance members are not guaranteed to be thread safe.",
"exceptionType": "System.NotSupportedException",
"stackTrace": " at System.Data.Entity.Core.Objects.ELinq.QueryParameterExpression.TryGetFieldOrPropertyValue(MemberExpression me, Object instance, Object& memberValue)
at System.Data.Entity.Core.Objects.ELinq.QueryParameterExpression.TryEvaluatePath(Expression expression, ConstantExpression& constantExpression)
at System.Data.Entity.Core.Objects.ELinq.QueryParameterExpression.EvaluateParameter(Object[] arguments)
at System.Data.Entity.Core.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable`1 forMergeOption)
at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClassc.
很有可能
where s.id == assessment.Lab_Space.id
在不适当的时间触发 Lab_Space 导航 属性 的延迟加载。
假设你没有像 Lab_Space_Id 这样的显式 FK 属性（如果你有，只需使用它而不是 Lab_Space.id），或者预先加载它（最好）：
var assessment = await context.EHS_Assessment_Audit.AsNoTracking()
.Include(x => x.Lab_Space) // <--
.Where(x => x.id == assessmentId).FirstOrDefaultAsync();
或在查询外对其求值：
var labSpaceId = assessment.Lab_Space.id; // <--
var lab = from s in context.Lab_Space.AsNoTracking()
where s.id == labSpaceId // <--
...
请注意，在原始查询中，assessment.Lab_Space 访问只是 记录在查询表达式树中 。实际评估（因此触发延迟加载）作为查询执行的一部分发生。