Reader.IsConsumed is false but object was disposed

Question

I'm using QueryMultiple which returns a GridReader.

Since I don't know how much data I'm gonna read, I'm looping over the reader with the stop condition of IsConsumed:

using (var reader = conn.QueryMultiple(mySql)) {
  while(!reader.IsConsumed) {
    reader.Read<...>
  }
}

However, I'm always getting an ObjectDisposedException on the last read. The value of IsConsumed is still false.

I've tried to pass DynamicParameters to the query with the intention of getting a callback (which seems to be useful via IParameterCallbacks), but I couldn't patch it together.

I would really rather not to have such an expected exception in the code. Thanks for any help.

I'm using SQL Server, my provider is System.Data.SqlClient in .NET 4.5, Dapper version 1.40.0.0

A failing test for example:

        [TestMethod]
        public void QueryMultipleWithCursor()
        {

            const string sql = @"
DECLARE @CurrentDate DATE
DECLARE DatesCursor CURSOR LOCAL FOR
    SELECT DISTINCT DataDate FROM Data_Table ORDER BY DataDate 
OPEN DatesCursor
FETCH NEXT FROM DatesCursor INTO @CurrentDate

WHILE @@FETCH_STATUS = 0 BEGIN

    SELECT DISTINCT
        DataDate AS Date1,
        DataDate AS Date2
        FROM Data_Table
        WHERE DataDate=@CurrentDate

    FETCH NEXT FROM DatesCursor INTO @CurrentDate
END
CLOSE DatesCursor
DEALLOCATE DatesCursor";

            using (var conn = _database.GetConnection())
            {
                    var reader = conn.QueryMultiple(sql);
                    while (!reader.IsConsumed)
                    {
                            reader.Read<DateTime, DateTime, DateTime>(
                                (date1, date2) => date1,
                                splitOn: "Date2").ToList();
                    }
            }
        }

I'm getting a NullReferenceException with the following stack:

at Dapper.SqlMapper.GridReader.NextResult() in D:\Dev\dapper-dot-net\Dapper NET40\SqlMapper.cs:line 4440
   at Dapper.SqlMapper.GridReader.<MultiReadInternal>d__9`8.System.IDisposable.Dispose()
   at Dapper.SqlMapper.GridReader.<MultiReadInternal>d__9`8.MoveNext() in D:\Dev\dapper-dot-net\Dapper NET40\SqlMapper.cs:line 4309
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at Dapper.SqlMapper.GridReader.Read[TFirst,TSecond,TReturn](Func`3 func, String splitOn, Boolean buffered) in D:\Dev\dapper-dot-net\Dapper NET40\SqlMapper.cs:line 4330
   at Project.MyTests.QueryMultipleWithCursor() in C:\Project\MyTests.cs:line 171
Result Message: 
Test method Project.MyTests.QueryMultipleWithCursor threw exception: 
System.NullReferenceException: Object reference not set to an instance of an object.

Re the edit: I set up a test rig with .NET 4.5, Dapper 1.40.0, `SqlClient`, and *it all worked fine*. http://pastie.org/10733819 - I'm happy to try and help - and if there's a bug: fix it. But I cannot reproduce the issue. Can you help me get an example that breaks in the way you describe? — Marc Gravell, Feb 23 '16 at 08:41
Can you try a stand alone test like Marc on same configuration and test, I wonder usage of same connection object in multiple context like parallel task, where you get reference of same GridReader and one of them read and close, thus consumed and other throwing an object disposed exception — Mrinal Kamboj, Feb 23 '16 at 09:58
I've added a failing unit test. I couldn't manage to reproduce the `ObjectDisposedException` with a simple enough test, but I got pretty close. I know the test is still complicated, but I don't see why it shouldn't work. — Mugen, Feb 23 '16 at 13:02

score 3 · Answer 1 · answered Feb 22 '16 at 15:53

I've pushed the following, which passes on SQL Server / SqlConnection; so it can work:

[Fact]
public void SO35554284_QueryMultipleUntilConsumed()
{
    using (var reader = connection.QueryMultiple(
        "select 1 as Id; select 2 as Id; select 3 as Id;"))
    {
        List<HazNameId> items = new List<HazNameId>();
        while (!reader.IsConsumed)
        {
            items.AddRange(reader.Read<HazNameId>());
        }
        items.Count.IsEqualTo(3);
        items[0].Id.IsEqualTo(1);
        items[1].Id.IsEqualTo(2);
        items[2].Id.IsEqualTo(3);
    }
}

I wonder if the issue here is a problem with a specific ADO.NET provider. You might want to specify exactly:

what backend RDBMS / etc you are using (SQL Server? Oracle? Postgresql? ...?)
what ADO.NET provider you are using
what runtime (.NET what.what? core-clr?) / OS you are using
what exact library version you are using (the above is against the source code, which is most similar to 1.50.0-beta8)

@Marc Gravell haven't tried, but how does this behave for absolutely no record for multiple Select, in current test there would be one record to consume — Mrinal Kamboj, Feb 23 '16 at 09:59
@MrinalKamboj good question; I'll change the test later to do 0, 1, 2, 3, ... etc selects — Marc Gravell, Feb 23 '16 at 16:54

score 1 · Answer 2 · answered Feb 23 '16 at 16:55

1

I am running into the same issue with Dapper and I am using the version 1.42.0 and SQL Server 2012 as the back end. Upon debugging I found that this issue is happening only when we try to create multiple objects using the Dapper's splitOn option on the last result set.

I have submitted a new issue on GitHub https://github.com/StackExchange/dapper-dot-net/issues/469

answered Feb 23 '16 at 16:55

sash

11
2

I see this would better fit as a comment as it's clearly not a solution to the problem. Welcome to SO, anyway! – phaberest Feb 23 '16 at 17:10
I realized it but the link "add a comment" is disabled and I could not add it as a comment. Actually it says, "You must have 50 reputation to comment" – sash Feb 23 '16 at 17:13
Actually identifying this as a bug is probably as best as I'll get – Mugen Feb 23 '16 at 17:21

score 0 · Accepted Answer · answered Feb 28 '16 at 12:01

Well it seems to be an issue with Dapper implementation, for the mean time I'm using both Dapper and SqlDataReader, which is more reliable:

public static SqlMapper.GridReader QueryMultipleStoredProcedure(this IDbConnection dbConnection, string spName, object parameters, out SqlDataReader sqlDataReader)
        {
            var gridReader = dbConnection.QueryMultiple(spName, new DynamicParameters(parameters), commandType: CommandType.StoredProcedure);
            sqlDataReader = typeof (SqlMapper.GridReader).GetInstanceField<SqlDataReader>(gridReader, "reader");
            return gridReader;
        }

        private static T GetInstanceField<T>(this Type type, object instance, string fieldName)
        {
            var bindFlags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic;
            var field = type.GetField(fieldName, bindFlags);
            return (T) field?.GetValue(instance);
        }

And then I can use sqlDataReader.HasRows

Reader.IsConsumed is false but object was disposed

3 Answers3