column X appears more than once - discriminators

oblivionsy · **Joined:** Fri Jun 01, 2007 4:55 pm **Posts:** 24

Hibernate version:
1.2.0.4000

Mapping documents:

Code:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
   <class name="GMBPDefinition.Classes.MatchStrings.BaseMatchString, GMBPDefinition" table="MatchingStrings">
      <id name="Id" column="ID" unsaved-value="0" type="Int32">
         <generator class="identity" />
      </id>
      <discriminator column="Type"/>
      
      <property name="MatchString"></property>
      <property name="isRegEx" column="isRegEx"></property>
      <property name="Type" column="Type"></property>

      <subclass name="GMBPDefinition.Classes.MatchStrings.TruncationString, GMBPDefinition"
               discriminator-value="1">
      </subclass>
      <subclass name="GMBPDefinition.Classes.MatchStrings.OutOfOfficeString, GMBPDefinition"
               discriminator-value="2">
      </subclass>
      <subclass name="GMBPDefinition.Classes.MatchStrings.BlackListString, GMBPDefinition"
               discriminator-value="3">
      </subclass>
   </class>
</hibernate-mapping>

Code between sessionFactory.openSession() and session.close():

Code:

Public Sub Save(ByVal MatchString As GMBPDefinition.Interfaces.IMatchString)
        Try
            MyBase.BeginTransaction()
            Session.Save(MatchString)
            MyBase.CommitTransaction()
        Catch ex As Exception
            MyBase.RollBackTransaction()
            Throw ex
        End Try
    End Sub

I am not sure why the Type column is being included twice. Any help would be greatly appreciated!

Thanks in advance

oblivionsy · **Joined:** Fri Jun 01, 2007 4:55 pm **Posts:** 24

Sorry, meant to paste the error in too!

Exception
"could not insert: [GMBPDefinition.Classes.MatchStrings.TruncationString][SQL: INSERT INTO MatchingStrings (MatchString, isRegEx, Type, Type) VALUES (?, ?, ?, '1')]"

inner exception:
"Column name 'Type' appears more than once in the result column list."

stack trace

" at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection)
at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection)
at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj)
at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj)
at System.Data.SqlClient.SqlDataReader.ConsumeMetaData()
at System.Data.SqlClient.SqlDataReader.get_MetaData()
at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString)
at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async)
at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result)
at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)
at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method)
at System.Data.SqlClient.SqlCommand.ExecuteDbDataReader(CommandBehavior behavior)
at System.Data.Common.DbCommand.System.Data.IDbCommand.ExecuteReader()
at NHibernate.Impl.BatcherImpl.ExecuteReader(IDbCommand cmd)
at NHibernate.Persister.Entity.AbstractEntityPersister.Insert(Object[] fields, Boolean[] notNull, SqlCommandInfo sql, Object obj, ISessionImplementor session)"

wolli · **Posted:** Mon Mar 16, 2009 3:36 am

Normally the descriminator isn't used in the code. It's just fpr hibernate to distinguish the classes. If you absolutely need to map the column, try

<property name="Type" column="Type" update="false" insert="false"/>

oblivionsy · **Joined:** Fri Jun 01, 2007 4:55 pm **Posts:** 24

That seemed to work well.

The way I load the class is a bit of a hack, while it is working, you might know a more elegant solution.

The trouble is, I do not know the type of the class when I load. It is just Load MatchString number 5 (for example) and this could be one of three classes.

My hack is to create a criterian object and list those with Id of 5. While this works, using the Load() method must be the correct way of doing it and getting back the correct concrete class.

Many thanks

wolli · **Posted:** Mon Mar 16, 2009 4:25 am

Quote:

My hack is to create a criterian object and list those with Id of 5. While this works, using the Load() method must be the correct way of doing it and getting back the correct concrete class.

I'm not sure what you mean. Can you post the criteria and the code for loading the objects ?

oblivionsy · **Joined:** Fri Jun 01, 2007 4:55 pm **Posts:** 24

Sure, here is my load method:

Code:

Dim Criteria As NHibernate.ICriteria
        Criteria = MyBase.Session.CreateCriteria(GetType(GMBPDefinition.Classes.MatchStrings.BaseMatchString))
        Criteria.Add(NHibernate.Expression.Expression.Eq("Id", Id))
        Dim list As IList(Of GMBPDefinition.Interfaces.IMatchString) = Criteria.List(Of GMBPDefinition.Interfaces.IMatchString)()

        If list.Count > 0 Then
            Return list(0)
        Else
            Return Nothing
        End If

Now you can see it is not useing the Session.Load() method.

I don't know which version of the class it will be (because that is controlled by the disciminator) so I can't pass in an object to load method.

I have tried variations, such as :

Code:

'Dim result As GMBPDefinition.Interfaces.IMatchString
        ''result = New GMBPDefinition.Classes.MatchStrings.BaseMatchString()

        'result = MyBase.Session.Load(Of GMBPDefinition.Classes.MatchStrings.BaseMatchString)(Id)
        ''MyBase.Session.Load(result, Id)
        'Return result

It did not like the passing of a Base Match String, and when it did load, the object could not be saved again as it was some NHibernate object that had not been initialised.

It is working, but there must be a better way to do it.

Thanks

wolli · **Posted:** Mon Mar 16, 2009 7:59 am

You don't have to pass a object:

BaseMatchString str =session.Load<BaseMatchString>(id);