NHibernate - Question marks instead of values in query

Question

Basically I have a Topic Object which can have multiple Category's associted with it. I'm trying to insert a new Category to a particular Topic and I get an error.

Working with ASP.NET 4 , also with windows-1255 encoding on the front-end and in ASP and hebrew_bin on MySQL (the back-end)

ISession session = dal.GetSession();
using (session.BeginTransaction())
{
    Topic t = session.Get<Topic>(topicId);
    Category c = new Category() { Name=name };
    t.AddCategory(c); // updates both references (inside `t` and inside `c`)
    session.Update(t);
    session.Save(c);
    session.Transaction.Commit();
}

Getting Error:

could not insert: [DAL.Models.Category#1][SQL: INSERT INTO Category (Name, Publish, TopicID, ID) VALUES (?, ?, ?, ?)]

Ultimately it fails because of a foreign key constraint violation (I guess ? is not a valid ID):

Cannot add or update a child row: a foreign key constraint fails (etladaatdb.category, CONSTRAINT FK6482F249B6E2851 FOREIGN KEY (ID) REFERENCES topic (ID))

Topic.cs:

public enum ColorEnum { Blue, Red, Green, Yellow }
    public class Topic
    {
        public virtual int ID { get; set; }
        public virtual string Name { get; set; }
        public virtual string Description { get; set; }
        public virtual string ImageUri { get; set; }
        public virtual ColorEnum Color { get; set; }

        public virtual IList<Category> Categories { get; set; }

        public virtual void AddCategory(Category c)
        {
            Categories.Add(c);
            c.Topic = this;
        }
    }

Topic.hbm.xml:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="DAL"
                   namespace="DAL.Models">
  <class name="Topic" lazy="true">
    <id name="ID">
      <generator class="increment"></generator>
    </id>
    <property name="Name" />
    <property name="Description" />
    <property name="ImageUri" />
    <property name="Color" type="ColorEnum" />

    <bag name="Categories" lazy="true" inverse="true"
                         batch-size="25" cascade="all-delete-orphan">
      <key column="ID" />
      <one-to-many class="Category" />
    </bag>
  </class>
</hibernate-mapping>

Category.cs:

public class Category
    {
        public virtual int ID { get; set; }
        public virtual string Name { get; set; }
        public virtual bool Publish { get; set; }

        public virtual Topic Topic { get; set; }
    }

Category.hbm.xml:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="DAL"
                   namespace="DAL.Models">
  <class name="Category" lazy="true">
    <id name="ID">
      <generator class="increment"></generator>
    </id>
    <property name="Name"/>
    <property name="Publish" />

    <many-to-one name="Topic" class="Topic" column="TopicID" />
  </class>
</hibernate-mapping>

Radim Köhler · Accepted Answer · 2015-08-10 13:54:03Z

1

It really seems, that you've just missed to assign topic to category. So this should do that trick:

// original
Category c = new Category() { Name=name };
t.AddCategory(c);
// always assign both sides during creation
c.Topic = t;

Now NHibernate will know what is the referenced Topic ... and will insert proper ID

About mapping. The relation many-to-one and one-to-many is expressed by exactly one column. It is the foreign key column in child (categories) table - TopicID.

So this is the correct mapping:

// Topic
<bag name="Categories" lazy="true" inverse="true"
                     batch-size="25" cascade="all-delete-orphan">
  // this is wrong
  // <key column="ID" />
  // this is the target column in the other table
  <key column="TopicID" />
  <one-to-many class="Category" />
</bag>

...

// Category
// the same columns for the same relation
<many-to-one name="Topic" class="Topic" column="TopicID" />

Having cascade in place, we can just save the topic:

session.Update(t);
// not needed, there is a cascade
// session.Save(c);

edited Aug 10, 2015 at 13:54

answered Aug 10, 2015 at 13:27

Radim Köhler

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3 Comments

Radim Köhler Over a year ago

Observed the mapping and found one issue. Relation is about one column for both sides...

Radim Köhler Over a year ago

Check my answer - the bag mapping would require <key column="TopicID" /> not the original <key column="ID" />

Radim Köhler Over a year ago

Amazing, enjoy mighty NHibernate, sir ;)

CodeTherapist · Accepted Answer · 2015-08-10 13:29:51Z

0

I think your entity is not complete and you should change your code. Do not forget to use a using statement for IDisposable objects.

using(ISession session = dal.GetSession())
{
using (session.BeginTransaction())
{
    Topic t = session.Get<Topic>(topicId);
    Category c = new Category() { Name=name };
    t.AddCategory(c);
    c.Topic = t;
    session.SaveOrUpdate(t);
    session.Transaction.Commit();
}
}

You could also inside your t.AddCategory(c); method:

public void AddCategory(Category category)
{
  // add to list
  category.Topic = this;
}

answered Aug 10, 2015 at 13:29

CodeTherapist

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