How to select child object without his parent

[Wojtek Baczyński]

Can anyone help me with simple crap?
I have many-to-one relation, Objects (parent) with really huge list of childs. Now when i do select of one particular child, hibernate is selecting also a parent. And becouse parent have many childrens, i get also many childrens.
But i want only this one child without a parent and others. What to do? Sure I can ingore other that but when list have 1000+ elements that is huge waste.

[Ankit Garg]

Tantummano please check your private messages for some administrative matter...

[Ankit Garg]

You can configure the parent property in child class to be lazy loaded, that way it won't be loaded automatically...

[Wojtek Baczyński]

Ankit thanks for your help but i've tried putting lazy="true" into many wird places and it never helps so could you be more specific? Please look at my simple files:

Site is parent and it have fields: Id, Name
Alias id child and it have: Id, SiteId, Name

So i don't know how to put lazy properitie to Alias file. I have lazy="true" in "<bag ..." in parent but it didn't seem to make any difference.
Tell me what should I change?

   <?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
  <class name="HelloWorld.Site, HelloWorld" table="Site">
    <id name="Id" column="ID" type="int">
      <generator class="native"></generator>
    </id>
    
    <property name="Name" column="name" type="String"></property>
    
    <bag name="Aliases" 
         cascade="all-delete-orphan" 
         lazy="true">
      
      <key column="SiteId" />
      <one-to-many class="HelloWorld.Alias" />
    </bag>
   
  </class>
</hibernate-mapping> 

   <?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
  <class name="HelloWorld.Alias, HelloWorld" table="Aliases">
    <id name="Id" column="ID" type="int">
      <generator class="native"></generator>
    </id>

    <property name="Name" column="name" type="String"></property>

    <many-to-one name="Site"
                     class="HelloWorld.Site"
                     column="SiteId"
                     cascade="none"
                     />
    
  </class>
</hibernate-mapping> 

[Ran Pleasant]

Wojtek Baczyński wrote:Can anyone help me with simple crap?
I have many-to-one relation, Objects (parent) with really huge list of childs. Now when i do select of one particular child, hibernate is selecting also a parent. And becouse parent have many childrens, i get also many childrens.
But i want only this one child without a parent and others. What to do? Sure I can ingore other that but when list have 1000+ elements that is huge waste.

This is actually a common design problem that is a performance killer. In select cases a child object does need to have a reference to its parent object. However, in the majority of cases there is not a *real* need for a child object to have a reference to the parent object. Circilar references between classes can also set you up for an endless loop. I would suggest taking a step back from your code, reviewing your design, and ask yourself if the child object really does needs a reference to the parent object.

[Wojtek Baczyński]

I think child don't need reference to parent at all. Simple ID (Foreign Key) would do the trick. But i thought that this lauzy reference is required to do one-to-many relation.

Clearly i don't like DB at all so forgive me if i am being noob.

I found something like solution i think. When i did that:

  IList aliasesList;
                Alias alias;
                using (ISession sessionN = factory.OpenSession())
                {
                    ICriteria sc = sessionN.CreateCriteria(typeof(Alias));
                    sc.Add(NHibernate.Criterion.Expression.Like("Id",
                        Convert.ToInt32(textBox1.Text)));
                    aliasesList = sc.List();
                    alias = (Alias)aliasesList[0];
                    tBox.Text += "\n" + alias.ToString();             
}
                 

Then I got two select's, one with all aliases from site and one with site.
But if i changed it that way:

  IList aliasesList;
                Alias alias;
                using (ISession sessionN = factory.OpenSession())
                {
                    ICriteria sc = sessionN.CreateCriteria(typeof(Alias));
                    sc.Add(NHibernate.Criterion.Expression.Like("Id",
                        Convert.ToInt32(textBox1.Text)));
                    aliasesList = sc.List();
                    alias = (Alias)aliasesList[0];
                         
}
 tBox.Text += "\n" + alias.ToString();       
                 

It gives only select to alias.
alias.ToString() is ovveriden by me and it is printing also parent field Site.Name
In second code which i pasted i of course got exception that I can't get into Site couse of lazy loading.
So it is kinda solution, i got only alias without site and other aliases.

[rakesh kanchalwar]

Wojtek Baczyński wrote:Can anyone help me with simple crap?
I have many-to-one relation, Objects (parent) with really huge list of childs. Now when i do select of one particular child, hibernate is selecting also a parent. And becouse parent have many childrens, i get also many childrens.
But i want only this one child without a parent and others. What to do? Sure I can ingore other that but when list have 1000+ elements that is huge waste.