The danger of renaming contentypes and how to fix it

Last week we experienced a hard problem to debug, but easy to solve. It was hard to debug because it didn’t happen in development or test environment, only in production environment after a deploy and the error message we got was not helping at all.

What was happening was that after the deploy to production the site crashed and gave us this message:
”Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.”
With the stacktrace:

“[SqlException (0x80131904): Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.]
   System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction) +1767866
   System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction) +5352418
   System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose) +244
   System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady) +1691
   System.Data.SqlClient.SqlDataReader.TryHasMoreRows(Boolean& moreRows) +322
   System.Data.SqlClient.SqlDataReader.TryReadInternal(Boolean setTimeout, Boolean& more) +230
   System.Data.SqlClient.SqlDataReader.TryNextResult(Boolean& more) +189
   System.Data.SqlClient.SqlDataReader.NextResult() +28
   System.Data.ProviderBase.DataReaderContainer.NextResult() +19
   System.Data.Common.DataAdapter.FillNextResult(DataReaderContainer dataReader) +51
   System.Data.Common.DataAdapter.FillFromReader(DataSet dataset, DataTable datatable, String srcTable, DataReaderContainer dataReader, Int32 startRecord, Int32 maxRecords, DataColumn parentChapterColumn, Object parentChapterValue) +233
   System.Data.Common.DataAdapter.Fill(DataSet dataSet, String srcTable, IDataReader dataReader, Int32 startRecord, Int32 maxRecords) +421
   System.Data.Common.DbDataAdapter.FillInternal(DataSet dataset, DataTable[] datatables, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior) +173
   System.Data.Common.DbDataAdapter.Fill(DataSet dataSet, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior) +316
   System.Data.Common.DbDataAdapter.Fill(DataSet dataSet) +88
   EPiServer.DataAccess.<>c__DisplayClassa.<DeleteDB>b__9() +240
   EPiServer.Data.Providers.<>c__DisplayClass7`1.<ExecuteTransaction>b__6() +200
   EPiServer.Data.Providers.SqlDeadlockRetryPolicy.Execute(Boolean isInTransaction, Func`1 method) +716
   EPiServer.Data.Providers.SqlDatabaseHandler.ExecuteTransaction(Func`1 action) +302
   EPiServer.DataAccess.ContentTypeDB.DeleteDB(Int32 pageTypeID) +171
   EPiServer.DataAccess.ContentTypeDB.Delete(ContentType contentType) +278
   EPiServer.DataAbstraction.DefaultContentTypeRepository.Delete(ContentType contentType) +174
   EPiServer.DataAbstraction.BlockTypeRepository.Delete(BlockType blockType) +40
   EPiServer.DataAbstraction.RuntimeModel.ContentTypeSynchronizer`2.Delete(T contentType) +104
   EPiServer.DataAbstraction.RuntimeModel.ContentTypeModelRegister`2.CommitTypes(Boolean deleteUnusedTypes) +365
   EPiServer.DataAbstraction.RuntimeModel.ContentTypeModelScanner`3.Sync(Boolean commitChanges) +131
   EPiServer.Initialization.ModelSyncInitialization.Initialize(InitializationEngine context) +580
   EPiServer.Framework.Initialization.<>c__DisplayClass5.<Initialize>b__4() +56
   EPiServer.Framework.Initialization.ModuleNode.Execute(Action a, String key) +73
   EPiServer.Framework.Initialization.ModuleNode.Initialize(InitializationEngine context) +141
   EPiServer.Framework.Initialization.InitializationEngine.InitializeModules() +445
   EPiServer.Framework.Initialization.InitializationEngine.Initialize(HostType hostType) +256
   EPiServer.Framework.Initialization.InitializationModule.Initialize(HostType hostType) +344
   EPiServer.Framework.Initialization.InitializationModule.FrameworkInitialization(HostType hostType) +78
   EPiServer.Global..ctor() +83
   SITENAME.Web.Global..ctor() +29
   ASP.global_asax..ctor() in c:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\root\8fc7b944\c53070aa\App_global.asax.0.cs:0”

In itself the message or stack trace was not helping us much at all more than telling us that something happen when EPiServer was initializing the site. Luckily for us, we had only made a couple of changes between the last deployment and this (the great thing of agile development!) so looking what those check in was about and the error message said we could narrow it down to a rename of a content type.
Why didn’t it happen in development or test? That is a good question and nothing I have the answer to, if you do, please tell me in a comment. I checked the database and there were no content created for this content type.
To solve the problem, we just added a migration to the project that looked like this:

    public class MigrateEducationListBLock : MigrationStep
    {
        public override void AddChanges()
        {
            ContentType("LocationEducationFavoritesListBlock")
                .UsedToBeNamed("EducationListBlock");
        }
    }