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问题:
I have this query and I get the error in this function:
var accounts = from account in context.Accounts from guranteer in account.Gurantors select new AccountsReport { CreditRegistryId = account.CreditRegistryId, AccountNumber = account.AccountNo, DateOpened = account.DateOpened, }; return accounts.AsEnumerable() .Select((account, index) => new AccountsReport() { RecordNumber = FormattedRowNumber(account, index + 1), CreditRegistryId = account.CreditRegistryId, DateLastUpdated = DateLastUpdated(account.CreditRegistryId, account.AccountNumber), AccountNumber = FormattedAccountNumber(account.AccountType, account.AccountNumber) }) .OrderBy(c=>c.FormattedRecordNumber) .ThenByDescending(c => c.StateChangeDate); public DateTime DateLastUpdated(long creditorRegistryId, string accountNo) { return (from h in context.AccountHistory where h.CreditorRegistryId == creditorRegistryId && h.AccountNo == accountNo select h.LastUpdated).Max(); }
Error is:
There is already an open DataReader associated with this Command which must be closed first.
Update:
stack trace added:
InvalidOperationException: There is already an open DataReader associated with this Command which must be closed first.] System.Data.SqlClient.SqlInternalConnectionTds.ValidateConnectionForExecute(SqlCommand command) +5008639 System.Data.SqlClient.SqlConnection.ValidateConnectionForExecute(String method, SqlCommand command) +23 System.Data.SqlClient.SqlCommand.ValidateCommand(String method, Boolean async) +144 System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result) +87 System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method) +32 System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method) +141 System.Data.SqlClient.SqlCommand.ExecuteDbDataReader(CommandBehavior behavior) +12 System.Data.Common.DbCommand.ExecuteReader(CommandBehavior behavior) +10 System.Data.EntityClient.EntityCommandDefinition.ExecuteStoreCommands(EntityCommand entityCommand, CommandBehavior behavior) +443 [EntityCommandExecutionException: An error occurred while executing the command definition. See the inner exception for details.] System.Data.EntityClient.EntityCommandDefinition.ExecuteStoreCommands(EntityCommand entityCommand, CommandBehavior behavior) +479 System.Data.Objects.Internal.ObjectQueryExecutionPlan.Execute(ObjectContext context, ObjectParameterCollection parameterValues) +683 System.Data.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption) +119 System.Data.Objects.ObjectQuery`1.System.Collections.Generic.IEnumerable.GetEnumerator() +38 System.Linq.Enumerable.Single(IEnumerable`1 source) +114 System.Data.Objects.ELinq.ObjectQueryProvider.b__3(IEnumerable`1 sequence) +4 System.Data.Objects.ELinq.ObjectQueryProvider.ExecuteSingle(IEnumerable`1 query, Expression queryRoot) +29 System.Data.Objects.ELinq.ObjectQueryProvider.System.Linq.IQueryProvider.Execute(Expression expression) +91 System.Data.Entity.Internal.Linq.DbQueryProvider.Execute(Expression expression) +69 System.Linq.Queryable.Max(IQueryable`1 source) +216 CreditRegistry.Repositories.CreditRegistryRepository.DateLastUpdated(Int64 creditorRegistryId, String accountNo) in D:\Freelance Work\SuperExpert\CreditRegistry\CreditRegistry\Repositories\CreditRegistryRepository.cs:1497 CreditRegistry.Repositories.CreditRegistryRepository.b__88(AccountsReport account, Int32 index) in D:\Freelance Work\SuperExpert\CreditRegistry\CreditRegistry\Repositories\CreditRegistryRepository.cs:1250 System.Linq.d__7`2.MoveNext() +198 System.Linq.Buffer`1..ctor(IEnumerable`1 source) +217 System.Linq.d__0.MoveNext() +96
回答1:
This can happen if you execute a query while iterating over the results from another query. It is not clear from your example where this happens because the example is not complete.
One thing that can cause this is lazy loading triggered when iterating over the results of some query.
This can be easily solved by allowing MARS in your connection string. Add MultipleActiveResultSets=true to the provider part of your connection string (where Data Source, Initial Catalog, etc. are specified).
回答2:
You can use the ToList() method before the return statement.
var accounts = from account in context.Accounts from guranteer in account.Gurantors select new AccountsReport { CreditRegistryId = account.CreditRegistryId, AccountNumber = account.AccountNo, DateOpened = account.DateOpened, }; return accounts.AsEnumerable() .Select((account, index) => new AccountsReport() { RecordNumber = FormattedRowNumber(account, index + 1), CreditRegistryId = account.CreditRegistryId, DateLastUpdated = DateLastUpdated(account.CreditRegistryId, account.AccountNumber), AccountNumber = FormattedAccountNumber(account.AccountType, account.AccountNumber)}).OrderBy(c=>c.FormattedRecordNumber).ThenByDescending(c => c.StateChangeDate).ToList(); public DateTime DateLastUpdated(long creditorRegistryId, string accountNo) { var dateReported = (from h in context.AccountHistory where h.CreditorRegistryId == creditorRegistryId && h.AccountNo == accountNo select h.LastUpdated).Max(); return dateReported; }
回答3:
Here is a working connection string for someone who needs reference.
回答4:
In my case, using Include() solved this error and depending on the situation can be a lot more efficient then issuing multiple queries when it can all be queried at once with a join.
IEnumerable users = db.Users.Include("Projects.Tasks.Messages"); foreach (User user in users) { Console.WriteLine(user.Name); foreach (Project project in user.Projects) { Console.WriteLine("\t"+project.Name); foreach (Task task in project.Tasks) { Console.WriteLine("\t\t" + task.Subject); foreach (Message message in task.Messages) { Console.WriteLine("\t\t\t" + message.Text); } } } }
回答5:
use the syntax .ToList() to convert object read from db to list to avoid being reread again..Hope that would work for it. Thanks.
回答6:
I donot know whether this is duplicate answer or not. If it is I am sorry. I just want to let the needy know how I solved my issue using ToList().
In my case I got same exception for below query.
int id = adjustmentContext.InformationRequestOrderLinks.Where(item => item.OrderNumber == irOrderLinkVO.OrderNumber && item.InformationRequestId == irOrderLinkVO.InformationRequestId).Max(item => item.Id);
I solved like below
List links = adjustmentContext.InformationRequestOrderLinks .Where(item => item.OrderNumber == irOrderLinkVO.OrderNumber && item.InformationRequestId == irOrderLinkVO.InformationRequestId).ToList(); int id = 0; if (links.Any()) { id = links.Max(x => x.Id); } if (id == 0) { //do something here }
回答7:
It appears that you're calling DateLastUpdated from within an active query using the same EF context and DateLastUpdate issues a command to the data store itself. Entity Framework only supports one active command per context at a time.
You can refactor your above two queries into one like this:
return accounts.AsEnumerable() .Select((account, index) => new AccountsReport() { RecordNumber = FormattedRowNumber(account, index + 1), CreditRegistryId = account.CreditRegistryId, DateLastUpdated = ( from h in context.AccountHistory where h.CreditorRegistryId == creditorRegistryId && h.AccountNo == accountNo select h.LastUpdated).Max(), AccountNumber = FormattedAccountNumber(account.AccountType, account.AccountNumber) }) .OrderBy(c=>c.FormattedRecordNumber) .ThenByDescending(c => c.StateChangeDate);
I also noticed you're calling functions like FormattedAccountNumber and FormattedRecordNumber in the queries. Unless these are stored procs or functions you've imported from your database into the entity data model and mapped correct, these will also throw excepts as EF will not know how to translate those functions in to statements it can send to the data store.
Also note, calling AsEnumerable doesn't force the query to execute. Until the query execution is deferred until enumerated. You can force enumeration with ToList or ToArray if you so desire.
回答8:
In addition to Ladislav Mrnka's answer:
If you are publishing and overriding container on Settings tab, you can set MultipleActiveResultSet to True. You can find this option by clicking Advanced... and it's going to be under Advanced group.
回答9:
回答10:
I solved this problem by changing await _accountSessionDataModel.SaveChangesAsync(); to _accountSessionDataModel.SaveChanges(); in my Repository class.
public async Task CreateSession() { var session = new Session(); _accountSessionDataModel.Sessions.Add(session); await _accountSessionDataModel.SaveChangesAsync(); }
Changed it to:
public Session CreateSession() { var session = new Session(); _accountSessionDataModel.Sessions.Add(session); _accountSessionDataModel.SaveChanges(); }
The problem was that I updated the Sessions in the frontend after creating a session (in code), but because SaveChangesAsync happens asynchronously, fetching the sessions caused this error because apparently the SaveChangesAsync operation was not yet ready.
回答11:
In my case, I had opened a query from data context, like
Dim stores = DataContext.Stores _ .Where(Function(d) filter.Contains(d.code)) _
... and then subsequently queried the same...
Dim stores = DataContext.Stores _ .Where(Function(d) filter.Contains(d.code)).ToList
Adding the .ToList to the first resolved my issue. I think it makes sense to wrap this in a property like:
Public ReadOnly Property Stores As List(Of Store) Get If _stores Is Nothing Then _stores = DataContext.Stores _ .Where(Function(d) Filter.Contains(d.code)).ToList End If Return _stores End Get End Property
Where _stores is a private variable, and Filters is also a readonly property that reads from AppSettings.
回答12:
I am using web service in my tool, where those service fetch the stored procedure. while more number of client tool fetches the web service, this problem arises. I have fixed by specifying the Synchronized attribute for those function fetches the stored procedure. now it is working fine, the error never showed up in my tool.
[MethodImpl(MethodImplOptions.Synchronized)] public static List MyDBFunction(string parameter1) { }
This attribute allows to process one request at a time. so this solves the Issue.
回答13:
For those finding this via Google;
I was getting this error because, as suggested by the error, I failed to close a SqlDataReader prior to creating another on the same SqlCommand, mistakenly assuming that it would be garbage collected when leaving the method it was created in.
I solved the issue by calling sqlDataReader.Close(); before creating the second reader.
回答14:
Well for me it was my own bug. I was trying to run an INSERT using SqlCommand.executeReader() when I should have been using SqlCommand.ExecuteNonQuery(). It was opened and never closed, causing the error. Watch out for this oversight.
回答15:
This is extracted from a real world scenario:
- Code works well in a Stage environment with MultipleActiveResultSets is set in the connection string
- Code published to Production environment without MultipleActiveResultSets=true
- So many pages/calls work while a single one is failing
- Looking closer at the call, there is an unnecessary call made to the db and needs to be removed
- Set MultipleActiveResultSets=true in Production and publish cleaned up code, everything works well and, efficiently
In conclusion, without forgetting about MultipleActiveResultSets, the code might have run for a long time before discovering a redundant db call that could be very costly, and I suggest not to fully depend on setting the MultipleActiveResultSets attribute but also find out why the code needs it where it failed.
