Fetching a lazy loaded component regression

[nfplee]

I have identified a regression introduced in version 5.3.0. It happens when trying to fetch a lazy loaded component which has a read-only property and is mapped as an interface.

It's a little querky to explain but I've tried to produce a minimal sample to show you the issue.

Please see the attached application (making sure to set the connection string). The database must have the following structure:

CREATE TABLE [dbo].[ContentItems](
	[Id] [int] IDENTITY(1,1) NOT NULL,
	[Name] [nvarchar](100) NOT NULL,
	[PageTitle] [nvarchar](1024) NULL
)

INSERT INTO [dbo].[ContentItems] ([Name]) VALUES ('Test')

SQL above edited after realising that the table must have data to reproduce.

  var contentItems = await session.Query<ContentItem>()
      .Fetch(i => i.Head)
      .ToListAsync();

Exception:

NHibernate.Exceptions.GenericADOException
  Message=could not execute query
[ select contentite0_.Id as id1_0_, contentite0_.Name as name2_0_, contentite0_.PageTitle as pagetitle3_0_ from ContentItems contentite0_ ]
  StackTrace:
   at NHibernate.Loader.Loader.<DoListAsync>d__38.MoveNext()
...

  This exception was originally thrown at this call stack:
  System.IndexOutOfRangeException: formula0_
   at System.Data.ProviderBase.BasicFieldNameLookup.GetOrdinal(String fieldName)
   at System.Data.SqlClient.SqlDataReader.GetOrdinal(String name)
   at NHibernate.Driver.NHybridDataReader.GetOrdinal(String name)
   at NHibernate.Type.NullableType.NullSafeGet(DbDataReader rs, String name, ISessionImplementor session)
   at NHibernate.Type.NullableType.NullSafeGet(DbDataReader rs, String[] names, ISessionImplementor session, Object owner)
   at NHibernate.Type.NullableType.NullSafeGetAsync(DbDataReader rs, String[] names, ISessionImplementor session, Object owner, CancellationToken cancellationToken)
--- End of stack trace from previous location ---
   at NHibernate.Type.ComponentType.HydrateAsync(DbDataReader rs, String[] names, ISessionImplementor session, Object owner, CancellationToken cancellationToken)
   at NHibernate.Persister.Entity.AbstractEntityPersister.HydrateAsync(DbDataReader rs, Object id, Object obj, String[][] suffixedPropertyColumns, ISet`1 fetchedLazyProperties, Boolean allProperties, Int32[] indexes, ISessionImplementor session, CancellationToken cancellationToken)
   at NHibernate.Loader.Loader.LoadFromResultSetAsync(DbDataReader rs, Int32 i, Object obj, ILoadable persister, EntityKey key, LockMode lockMode, ILoadable rootPersister, ISessionImplementor session, CancellationToken cancellationToken)
   at NHibernate.Loader.Loader.InstanceNotYetLoadedAsync(DbDataReader dr, Int32 i, ILoadable persister, EntityKey key, LockMode lockMode, EntityKey optionalObjectKey, Object optionalObject, IList hydratedObjects, ISessionImplementor session, CancellationToken cancellationToken)
   at NHibernate.Loader.Loader.GetRowAsync(DbDataReader rs, ILoadable[] persisters, EntityKey[] keys, Object optionalObject, EntityKey optionalObjectKey, LockMode[] lockModes, IList hydratedObjects, ISessionImplementor session, Boolean mustLoadMissingEntity, Action`2 cacheBatchingHandler, CancellationToken cancellationToken)
   at NHibernate.Loader.Loader.GetRowFromResultSetAsync(DbDataReader resultSet, ISessionImplementor session, QueryParameters queryParameters, LockMode[] lockModeArray, EntityKey optionalObjectKey, IList hydratedObjects, EntityKey[] keys, Boolean returnProxies, IResultTransformer forcedResultTransformer, QueryCacheResultBuilder queryCacheResultBuilder, Action`2 cacheBatchingHandler, CancellationToken cancellationToken)
   at NHibernate.Loader.Loader.DoQueryAsync(ISessionImplementor session, QueryParameters queryParameters, Boolean returnProxies, IResultTransformer forcedResultTransformer, QueryCacheResultBuilder queryCacheResultBuilder, CancellationToken cancellationToken)
   at NHibernate.Loader.Loader.DoQueryAndInitializeNonLazyCollectionsAsync(ISessionImplementor session, QueryParameters queryParameters, Boolean returnProxies, IResultTransformer forcedResultTransformer, QueryCacheResultBuilder queryCacheResultBuilder, CancellationToken cancellationToken)
   at NHibernate.Loader.Loader.DoListAsync(ISessionImplementor session, QueryParameters queryParameters, IResultTransformer forcedResultTransformer, QueryCacheResultBuilder queryCacheResultBuilder, CancellationToken cancellationToken)

Test NHibernate.zip

[bahusoid]

You should provide exception stacktrace and problematic query in issue description to make it more clear.

Also please use https://github.com/nhibernate/nhibernate-core-testcase for providing reproduction solutions in future (see GH0000 folder with test templates)

Ok. I executed your solution and everything seems to work OK for me with my connection string (at least no exceptions) using 5.3.0 and 5.3.13. See no regressions so far...

[bahusoid]

I uncommented ThenFetch(h => h.Title) part and now it throws in 5.3:

System.InvalidOperationException: Property Head.Title does not exist on entity ConsoleApp1.Models.ContentItem
   at NHibernate.Persister.Entity.AbstractEntityPersister.PropertySelectFragment(String name, String suffix, ICollection`1 fetchProperties, Boolean allProperties)
   at NHibernate.Hql.Ast.ANTLR.Tree.SelectClause.RenderNonScalarProperties(ASTAppender appender, FromElement fromElement, Int32 nonscalarSize, Int32 k)
   at NHibernate.Hql.Ast.ANTLR.Tree.SelectClause.RenderNonScalarSelects(ISelectExpression[] selectExpressions, FromClause currentFromClause)
   at NHibernate.Hql.Ast.ANTLR.Tree.SelectClause.InitializeExplicitSelectClause(FromClause fromClause)
   at NHibernate.Hql.Ast.ANTLR.HqlSqlWalker.ProcessQuery(IASTNode select, IASTNode query)
   at NHibernate.Hql.Ast.ANTLR.HqlSqlWalker.unionedQuery()
   at NHibernate.Hql.Ast.ANTLR.HqlSqlWalker.query()
   at NHibernate.Hql.Ast.ANTLR.HqlSqlWalker.selectStatement()
   at NHibernate.Hql.Ast.ANTLR.HqlSqlWalker.statement()
   at NHibernate.Hql.Ast.ANTLR.HqlSqlWalker.Transform()
   at NHibernate.Hql.Ast.ANTLR.HqlSqlTranslator.Translate()
   ...

But it doesn't work in 5.2.7 either (different exception though)

NHibernate.Hql.Ast.ANTLR.InvalidPathException: Invalid join: _0.Title [.ThenFetch[ConsoleApp1.Models.ContentItem, ConsoleApp1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null,ConsoleApp1.Models.IHead, ConsoleApp1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null,System.String, System.Private.CoreLib, Version=6.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e](.Fetch[ConsoleApp1.Models.ContentItem, ConsoleApp1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null,ConsoleApp1.Models.IHead, ConsoleApp1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null](NHibernate.Linq.NhQueryable`1[ConsoleApp1.Models.ContentItem], Quote((i, ) => (i.Head)), ), Quote((h, ) => (h.Title)), )]
   at NHibernate.Hql.Ast.ANTLR.HqlSqlWalker.CreateFromJoinElement(IASTNode path, IASTNode alias, Int32 joinType, IASTNode fetchNode, IASTNode propertyFetch, IASTNode with)
   at NHibernate.Hql.Ast.ANTLR.HqlSqlWalker.joinElement()
   at NHibernate.Hql.Ast.ANTLR.HqlSqlWalker.fromElement()
   at NHibernate.Hql.Ast.ANTLR.HqlSqlWalker.fromElementList()
   at NHibernate.Hql.Ast.ANTLR.HqlSqlWalker.fromClause()
   at NHibernate.Hql.Ast.ANTLR.HqlSqlWalker.unionedQuery()
   at NHibernate.Hql.Ast.ANTLR.HqlSqlWalker.query()
   at NHibernate.Hql.Ast.ANTLR.HqlSqlWalker.selectStatement()
   at NHibernate.Hql.Ast.ANTLR.HqlSqlWalker.statement()
   at NHibernate.Hql.Ast.ANTLR.HqlSqlTranslator.Translate()
...

So please clarify what regression are you talking about?

[nfplee]

Thanks for the link in producing a test case. I'm not interested in the ThenFetch part, that was just me experimenting as I'm going to Lazy load the entire component,

[nfplee]

@bahusoid sorry I mis-read your reply as I was at a funeral. I can't work out why you can't reproduce this. Please note the error I'm getting is:

IndexOutOfRangeException: formula0_

I am using MS SQL Server as I couldn't reproduce the error using SQLite.

I'm currently working on a test case.

[bahusoid]

Ok. Waiting for failed test.

Regarding your mappings:

Property(x => x.DummyFieldToLoadEmptyComponent, m =>
{
	m.Access(Accessor.ReadOnly);
	m.Formula("1");
});

Readonly access means that property is not used for entity loading:

readonly - Access the mapped property through a Property get to get the value and do nothing to set the value. This is useful to allow calculated properties in the domain that will never be recovered from the DB but can be used for querying.

So it shouldn't affect Fetch in any way. And in your query session.Query<ContentItem>().Fetch(i => i.Head).ToListAsync() -readonly property is simply ignored. So are you sure you provided correct failing query in sample?

[nfplee]

Yeah I literally removed my connection string and zipped it up. I'm struggling to produce my test case as it keeps on passing. Is there a way to target a particular database/dialect?

Thanks for the additional information regarding read-only. Ideally I wouldn't need this property but I can't see how else I can force NHibernate not to make the component nullable (since when all properties of the component are null then the component is null). One idea is to change the head property to:

private IHead _head;
public virtual IHead Head {
    get => _head ??= new Head();
    set => _head = value;
}

But this requires access to the concrete class which unfortunately I don't have because of the way my application is abstracted.

[bahusoid]

Maybe it's a data specific issue. As I'm running it on empty database. And it looks like you have some data in you SQL Server database where issue is reproducible and fails to reproduce on empty SQLite database too.

[nfplee]

Thanks @bahusoid, I hadn't expected the data to cause a problem. As you discovered the issue doesn't happen with an empty table. However if you populate one record inside it then hopefully you should see the problem.

I'm still unable to re-produce a test case for this. Here's what I have come up with so far:

GH3164.zip

Thanks again for your help so far.

[bahusoid]

Is there a way to target a particular database/dialect?

Specify it in hibernate.cfg.xml. Something like:

    <property name="dialect">NHibernate.Dialect.MsSql2008Dialect</property>
    <property name="connection.driver_class">NHibernate.Driver.Sql2008ClientDriver</property>
    <property name="connection.connection_string">YOUR_CONNECTION_STRING</property>

Or override it by code. Something like:

protected override void Configure(Configuration configuration)
{
	configuration.DataBaseIntegration(x =>
	{
		x.Dialect<MsSql2008Dialect>();
		x.ConnectionString = "YOUR_CONNECTION_STRING";
		x.Driver<Sql2008ClientDriver>();
	}
	);
	base.Configure(configuration);
}

Also you don't need to rewrite existing mappings. Instead of writing mapper.Class<Entity> ...) you can reuse existing mapping class via mapper.AddMapping<ContentItemMapping>() or mapper.AddMapping<HeadMapping>()

[bahusoid]

No. Seems it's not as simple as that.

Ignore it. I reproduced it.

[nfplee]

Thanks, I'm glad you can reproduce.

Also you don't need to rewrite existing mappings. Instead of writing mapper.Class ...) you can reuse existing mapping class via mapper.AddMapping() or mapper.AddMapping()

Yeah I know but I found it easier to modify if it was all within 1 file.