Question

I’ve got a weird exception when I execute an nHibernate LINQ query.
If I write


var address = new Address {Id = Guid.Empty};
session.Query().Where(x=> x == address).ToList();


Than I get

object references an unsaved transient instance – save the transient
instance before flushing or set cascade action for the property to
something that would make it autosave. Type: DomainModel.Address,
Entity: DomainModel.Address

at
NHibernate.Engine.ForeignKeys.GetEntityIdentifierIfNotUnsaved(String
entityName, Object entity, ISessionImplementor session) at
NHibernate.Type.EntityType.GetIdentifier(Object value,
ISessionImplementor session) at
NHibernate.Type.ManyToOneType.NullSafeSet(IDbCommand cmd, Object
value, Int32 index, ISessionImplementor session) at
NHibernate.Param.NamedParameterSpecification.Bind(IDbCommand command,
IList1 multiSqlQueryParametersList, Int32 singleSqlParametersOffset,
IList1 sqlQueryParametersList, QueryParameters queryParameters,
ISessionImplementor session) at
NHibernate.Param.NamedParameterSpecification.Bind(IDbCommand command,
IList1 sqlQueryParametersList, QueryParameters queryParameters,
ISessionImplementor session) at
NHibernate.SqlCommand.SqlCommandImpl.Bind(IDbCommand command,
ISessionImplementor session) at
NHibernate.Loader.Loader.PrepareQueryCommand(QueryParameters
queryParameters, Boolean scroll, ISessionImplementor session) at
NHibernate.Loader.Loader.DoQuery(ISessionImplementor session,
QueryParameters queryParameters, Boolean returnProxies) at
NHibernate.Loader.Loader.DoQueryAndInitializeNonLazyCollections(ISessionImplementor
session, QueryParameters queryParameters, Boolean returnProxies) at
NHibernate.Loader.Loader.DoList(ISessionImplementor session,
QueryParameters queryParameters) at
NHibernate.Loader.Loader.ListIgnoreQueryCache(ISessionImplementor
session, QueryParameters queryParameters) at
NHibernate.Loader.Loader.List(ISessionImplementor session,
QueryParameters queryParameters, ISet1 querySpaces, IType[]
resultTypes) at
NHibernate.Hql.Ast.ANTLR.Loader.QueryLoader.List(ISessionImplementor
session, QueryParameters queryParameters) at
NHibernate.Hql.Ast.ANTLR.QueryTranslatorImpl.List(ISessionImplementor
session, QueryParameters queryParameters) at
NHibernate.Engine.Query.HQLQueryPlan.PerformList(QueryParameters
queryParameters, ISessionImplementor session, IList results) at
NHibernate.Impl.SessionImpl.List(IQueryExpression queryExpression,
QueryParameters queryParameters, IList results) at
NHibernate.Impl.AbstractSessionImpl.List(IQueryExpression
queryExpression, QueryParameters parameters) at
NHibernate.Impl.ExpressionQueryImpl.List() at
NHibernate.Linq.DefaultQueryProvider.ExecuteQuery(NhLinqExpression
nhLinqExpression, IQuery query, NhLinqExpression nhQuery) at
NHibernate.Linq.DefaultQueryProvider.Execute(Expression expression)
at NHibernate.Linq.DefaultQueryProvider.Execute[TResult](Expression
expression) at Remotion.Linq.QueryableBase1.GetEnumerator() at
System.Linq.Buffer1..ctor(IEnumerable1 source) at
System.Linq.Enumerable.ToArray[TSource](IEnumerable1 source)

However, if I Write


var person = new Person {Id = Guid.Empty};
session.Query().Where(x=> x == person).ToList();


everything works fine. The only difference between the two classes and related mapping is that Address is mapped using the < class /> tag while Person belongs to an inheritance mapping, Party => Person and is mapped using < joined-subclass />

I know that I can rewrite the query using the Key fields rather than the object, however this is only a really simplified version of the problem and this solution is not applicable.

Any idea on this behavior ?

Thanks,
Marco

Answer 1

Have a look at QBE (Query By Example) :

• NHibernate : Query by example on primary key produces "WHERE (1=1)"
• Mixing Likes and Equals with NHibernate Query-By-Example?