I'm trying to follow the interception example shown here to get it working with EF 6 but running into a problem with the function RewriteFullTextQuery as shown in Figure 1. The interception seems to work but it does not actually execute the logic in the for loop of the RewriteFullTextQuery method because the cmd.Parameters.Count is always zero. Furthermore the cmd.CommandText property seems to be displaying the correct SQL query which I take as another piece of evidence that the interception is working correctly.
Figure 1: RewriteFullTextQuery Code Excerpt
public static void RewriteFullTextQuery(DbCommand cmd)
{
string text = cmd.CommandText;
for (int i = 0; i < cmd.Parameters.Count; i++)
{
DbParameter parameter = cmd.Parameters[i];
if (parameter.DbType.In(DbType.String, DbType.AnsiString, DbType.StringFixedLength, DbType.AnsiStringFixedLength))
{
The RewriteFullTextQuery function is being called by the ReaderExecuting function shown in Figure 2 which gives it the command argument that is causing all the trouble.
Figure 2: ReaderExecuting Function
public void ReaderExecuting(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
{
RewriteFullTextQuery(command);
}
Even though my code isn't exactly the same as the example, the interception seems to be working so it is making me wonder what conditions is it that will populate the command to have a Parameters.Count of more than zero?
It works only if you pass the parameter to the query as a variable. If you use a literal EF won't use parameters.
I mean, this won't generate any parameter
context.Notes.Where(_ => _.NoteText == "CompareValue").Count();
This will
string compareValue = "CompareValue";
context.Notes.Where(_ => _.NoteText == compareValue).Count();
It turns out that it is because of the way Entity Framework generates the SQL. If you pass in a string literal as your search value to your LINQ statement it does not generate a SQL that makes use of a parameter. But if you pass in your search value as a variable, it will generate the SQL that utilizes a parameter. A solution (for dynamic queries) and more details can be found on this blog.
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<T>.GetEnumerator() +38
System.Linq.Enumerable.Single(IEnumerable`1 source) +114
System.Data.Objects.ELinq.ObjectQueryProvider.<GetElementFunction>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.<AccountDetails>b__88(AccountsReport account, Int32 index) in D:\Freelance Work\SuperExpert\CreditRegistry\CreditRegistry\Repositories\CreditRegistryRepository.cs:1250
System.Linq.<SelectIterator>d__7`2.MoveNext() +198
System.Linq.Buffer`1..ctor(IEnumerable`1 source) +217
System.Linq.<GetEnumerator>d__0.MoveNext() +96
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).
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;
}
Use the syntax .ToList() to convert object read from db to list to avoid being re-read again.
Here is a working connection string for someone who needs reference.
<connectionStrings>
<add name="IdentityConnection" connectionString="Data Source=(LocalDb)\v11.0;AttachDbFilename=|DataDirectory|\IdentityDb.mdf;Integrated Security=True;MultipleActiveResultSets=true;" providerName="System.Data.SqlClient" />
</connectionStrings>
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<User> 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);
}
}
}
}
I dont 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<Entities.InformationRequestOrderLink> 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
}
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.
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) Filters.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.
As a side-note...this can also happen when there is a problem with (internal) data-mapping from SQL Objects.
For instance...
I created a SQL Scalar Function that accidentally returned a VARCHAR...and then...used it to generate a column in a VIEW. The VIEW was correctly mapped in the DbContext...so Linq was calling it just fine. However, the Entity expected DateTime? and the VIEW was returning String.
Which ODDLY throws...
"There is already an open DataReader associated with this Command
which must be closed first"
It was hard to figure out...but after I corrected the return parameters...all was well
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.
I solved this problem by changing
await _accountSessionDataModel.SaveChangesAsync();
to
_accountSessionDataModel.SaveChanges();
in my Repository class.
public async Task<Session> 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.
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.
Most likely this issue happens because of "lazy loading" feature of Entity Framework. Usually, unless explicitly required during initial fetch, all joined data (anything that stored in other database tables) is fetched only when required. In many cases that is a good thing, since it prevents from fetching unnecessary data and thus improve query performance (no joins) and saves bandwidth.
In the situation described in the question, initial fetch is performed, and during "select" phase missing lazy loading data is requested, additional queries are issued and then EF is complaining about "open DataReader".
Workaround proposed in the accepted answer will allow execution of these queries, and indeed the whole request will succeed.
However, if you will examine requests sent to the database, you will notice multiple requests - additional request for each missing (lazy loaded) data. This might be a performance killer.
A better approach is to tell to EF to preload all needed lazy loaded data during the initial query. This can be done using "Include" statement:
using System.Data.Entity;
query = query.Include(a => a.LazyLoadedProperty);
This way, all needed joins will be performed and all needed data will be returned as a single query. The issue described in the question will be solved.
The same error happened to me when I was looping and updating data on
IEnumerable<MyClass>
When I changed the looped-on collection to be List<MyClass>, and filled it by converting by .ToList(), it solved and updated without any errors.
I had the same error, when I tried to update some records within read loop.
I've tried the most voted answer MultipleActiveResultSets=true and found, that it's just workaround to get the next error
New transaction is not allowed because there are other threads running
in the session
The best approach, that will work for huge ResultSets is to use chunks and open separate context for each chunk as described in
SqlException from Entity Framework - New transaction is not allowed because there are other threads running in the session
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.
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.
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<t> MyDBFunction(string parameter1)
{
}
This attribute allows to process one request at a time. so this solves the Issue.
In my case, I had to set the MultipleActiveResultSets to True in the connection string.
Then it appeared another error (the real one) about not being able to run 2 (SQL) commands at the same time over the same data context! (EF Core, Code first)
So the solution for me was to look for any other asynchronous command execution and turn them to synchronous, as I had just one DbContext for both commands.
I hope it helps you
Having some problems with my Silverlight app (with RIA services) filtering my results. The idea is on the client I set up the EntityQuery and its filters and call load. However this isn't working for me.
Heres my code.
public void FireQuery(string filterValue)
{
EntityQuery<Parent> query = m_ParentDomainContext.GetParentQuery();
query = query.Where(p => p.Children.Any(c => c.Name.Contains(filterValue)));
m_ParentDomainContext.Load(query, Query_Completed, null);
}
Compiles just fine, however, runtime I get "Query operator 'Any' is not supported." Exception.
Does anyone know of a good way to filter like this? Again, I'm looking for a way to set this up on the client.
EDIT: I should note, I've tried a few other queries as well, with similar results:
query = query.Where(p => p.Children.Where(c => c.Name.Contains(filterValue)).Count() != 0);
query = query.Where(p => p.Children.Where(c => c.Name.Contains(filterValue)).FirstOrDefault != null);
query = query.Where(p => p.Children.Where(c => c.Name.Contains(filterValue)).Any());
Query Operator 'Count/FirstOrDefault/Any' is not supported. I'm clearly missing something here...
As I tried to play around a little with this, I figured out that methods like First, Any and Count can't be used with LINQ to Entities (and, I believe, even NHibernate) over WCF RIA Services because they're not defined on the IQueryable itself, but, instread, are extention methods defined in the System.Linqnamespace. That is precisely why this shows as a run-time exception and not a compile-time error. The only extension methods that can be used here are those found in System.ServiceModel.DomainServices.Client (such as Where, Skip, Take, OrderBy, etc.).
This has to do with the "EntityQuery" objects, because those need to be composed and sent back to the server, whereas for the collections (such as m_ParentDomainContext.Parents in your case), you can use the System.Linq extension methods freely.
In order to implement this functionality, I suggest, as Thomas Levesque said, to expose it from the server in order to only get the data you want, or, alternatively, you can compose a query using the available constructs (the ones in System.ServiceModel.DomainServices.Client) and then apply the other filters on the resulting data (where you can use extension methods from the System.Linq namespace).
PS: I tried this with both classic Entity Framework and Entity Framework CodeFirst, and had the same results.
I hope this helps
On this question I solved the problem of querying Google Datastore to retrieve stuff by user (com.google.appengine.api.users.User) like this:
User user = userService.getCurrentUser();
String select_query = "select from " + Greeting.class.getName();
Query query = pm.newQuery(select_query);
query.setFilter("author == paramAuthor");
query.declareParameters("java.lang.String paramAuthor");
greetings = (List<Greeting>) query.execute(user);
The above works fine - but after a bit of messing around I realized this syntax in not very practical as the need to build more complicated queries arises - so I decided to manually build my filters and now I got for example something like the following (where the filter is usually passed in as a string variable but now is built inline for simplicity):
User user = userService.getCurrentUser();
String select_query = "select from " + Greeting.class.getName();
Query query = pm.newQuery(select_query);
query.setFilter("author == '"+ user.getEmail() +"'");
greetings = (List<Greeting>) query.execute();
Obviously this won't work even if this syntax with field = 'value' is supported by JDOQL and it works fine on other fields (String types and Enums). The other strange thing is that looking at the Data viewer in the app-engine dashboard the 'author' field is stored as type User but the value is 'user#gmail.com', and then again when I set it up as parameter (the case above that works fine) I am declaring the parameter as a String then passing down an instance of User (user) which gets serialized with a simple toString() (I guess).
Anyone any idea?
Using string substitution in query languages is always a bad idea. It's far too easy for a user to break out and mess with your environment, and it introduces a whole collection of encoding issues, etc.
What was wrong with your earlier parameter substitution approach? As far as I'm aware, it supports everything, and it sidesteps any parsing issues. As far as the problem with knowing how many arguments to pass goes, you can use Query.executeWithMap or Query.executeWithArray to execute a query with an unknown number of arguments.
I use the code below as an HTMLHelper which gets data from the database and loops over it to display a menu. This is fairly straightforward as you can see however, what if you have a database table using the adjacent model of hierarchies eg/ID, ParentID, OrderID. Easy to see whats going on but recursion is needed to get this data out properly. Is writing a C# recursive function acceptable? If so can someone help me with that? The expected output is something similar to this..
<ul>
<li>Item1
<ul>
<li>SubItem1</li>
</ul>
</li>
</ul>
SQL 2008 has a Hierarchy datatype now so I am not sure if this will help things?
I would also like some way of enabling users to decide what goes in a menu for example, a list of items that can go in the menu and then choosing these items and their positions in the hierarchy. Once a saved button is pressed it will store this heirarchy in the database.
Am I asking too much, I'm sure this must be quite a common scenario?
Here is my HTMLHelper code if anyone wants to use it...
public static string Menu(this HtmlHelper helper, int MenuCat)
{
string menuHTML = "<ul id=\"menu\">";
var route = helper.ViewContext.RequestContext.RouteData;
string currentPageName = route.GetRequiredString("id");
DB db = DB.CreateDB();
//var result = from p in db.WebPages where p.CategoryID == 9 select p;
var result = from p in db.WebPages select p;
foreach (var item in result)
{
if (item.Name == currentPageName)
{
menuHTML += "\n\t<li>" + helper.ActionLink(item.Name, "Details", "Dinner", new { id = item.ID }, new { #class = "selected" }) + "</li>";
}
else
{
menuHTML += "\n\t<li>" + helper.ActionLink(item.Name, "Details", "Dinner", new { id = item.ID }, null) + "</li>";
}
}
menuHTML += "\n</ul>\n";
return menuHTML;
}
I would do two things here: don't bother rendering this yourself: use jQuery. If you Google "jquery menu" you'll find hundreds of links.
Next, put the ordering logic on your app, you don't need the DB to do this as it soaks up cycles and (from what I've read) isn't terribly efficient. This is simple looping logic with a self-referencing join that Linq is perfect for.
Hand this off to jQuery, adn you're good to go without hard-coding HTML in code :)
If you are using Sql server 2005 take a look to Common Table Expression (CTE) (google with CTE hierarchical data). It allows you to create a view displaying the complete hierarchy.
But, how much depth level are you displaying in the menu? Usually you only need to show directy childs and go down in the hierarchy as the user clicks the links. (No recursion needed)
I always use recursive table-valued functions for fetching hierarchical data in SQL server.
See an example here:
blogs.conchango.com/christianwade/archive/2004/11/09/234.aspx
Unfortunately, there is a recursion limit (32 levels maximum) for SQL Server User Defined Functions (UDF) and Stored Procedures.
Note: If you use a table-valued function just drop it in your dbml file and you will be able to access it like any other table.
Another approach is to use the a new recursive queries syntax (in the form of the WITH clause and Common Table Expressions-CTE) introduced in SQL Server 2005.
Take a look here:
www.eggheadcafe.com/articles/sql_server_recursion_with_clause.asp
An approach of mixing CTE with Linq-To-SQL is presented here:
stackoverflow.com/questions/584841/common-table-expression-cte-in-linq-to-sql