NHibernate - simple join query

Question

A very simple scenario. I have 2 classes: Project and DataStructure. Class Project contains member List<DataStructure>. My goal is to load a Project and all its DataStructures in one call.

public class Project
{
    public virtual string Id { get { } set { } }
    public virtual string Name { get { } set { } }
    public virtual ISet<DataStructure> DataStructures { get { } set { } }
}

public class DataStructure
{
    public virtual string Id { get { } set { } }
    public virtual string Name { get { } set { } }
    public virtual string Description { get { } set { } }
    public virtual Project Project { get { } set { } }
    public virtual IList<DataField> Fields { get { } set { } }
}

Note that DataStructure also contains a list of class DataField but I don’t want to load these right now.

Mapping in Fluent NHibernate:

public class ProjectMap : ClassMap<Project>
{
    public ProjectMap()
    {
        Table("PROJECTS");
        Id(x => x.Pk, "PK");
        Map(x => x.Id, "ID");
        Map(x => x.Name, "NAME");
        HasMany<DataStructure>(x => x.DataStructures).KeyColumn("FK_PROJECT");
    }
}

public class DataStructureMap : ClassMap<DataStructure>
{
    public DataStructureMap()
    {
        Table("DATA_STRUCTURES");
        Map(x => x.Id, "ID");
        Map(x => x.Name, "NAME");
        Map(x => x.Description, "DESCRIPTION");
        References<Project>(x => x.Project, "FK_PROJECT");
        HasMany<DataField>(x => x.Fields).KeyColumn("FK_DATA_STRUCTURE");
    }
}

This is my query:

using (ISession session = SessionFactory.OpenSession())
{
    IQuery query = session.CreateQuery("from Project left join DataStructure");
    project = query.List<Project>();
}

The result is this exception:

NHibernate.Hql.Ast.ANTLR.SemanticException: Path expected for join! [from Themis.DataEntities.Project left join DataStructure]

Do I need to specify the field for the join? Isn’t that inferred from the mappings?

Note1 – Table PROJECTS contains a single Project row so there is no need to search for a specific one.

Note2 – I verified that my NHibernate setup is correct by successfully loading just the Project.

Yoav · Accepted Answer · 2011-01-14 17:42:21Z

2

For anyone who is interested I found the answer on nhusers:

IQuery query = session.CreateQuery("from Project as pr left join pr.DataStructures")

answered Jan 14, 2011 at 17:42

Yoav

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Comments

Egor Pavlikhin · Accepted Answer · 2011-01-13 23:45:21Z

1

Your query should be "from Project left join Project.Fields". Project.DataStructures is the path that NH expects to see. Remember that it's object oriented, not table oriented, so most of the time even your queries operate on objects.

edited Jan 13, 2011 at 23:45

answered Jan 13, 2011 at 23:08

Egor Pavlikhin

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3 Comments

ChrisAnnODell Over a year ago

Good answer, but I think you mean Project.DataStructures, which I would correct for you if I had the rep.

Yoav Over a year ago

I changed the query to IQuery query = session.CreateQuery("from Project left join Project.DataStructures"); Now I get a slightly different error: NHibernate.Hql.Ast.ANTLR.InvalidPathException: Invalid path: 'Project.DataStructures' [from Themis.DataEntities.Project left join Project.DataStructures]

Egor Pavlikhin Over a year ago

Try specifying namespace for Project.DataStructures too like Themis.DataEntities.Project.DataStructures

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