one-to-one and what else (in the C# code)

rolandz · **Posted:** Wed Jan 11, 2006 4:20 am

Hi everyone,

I've a class Picture and Data with one to one relationship (Data instance is being contained by Picture instance). I have the following mappings defined:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
<class name="Pix.Data.Picture, Pix.Data" table="OBJECT">
<id name="Id" column="ID" type="Int32" unsaved-value="0" access="field">
<generator class="sequence">
<param name="sequence">OBJECT_ID_GEN</param>
</generator>
</id>
<property name="Name" column="NAME" type="String" access="field" />
<property name="Path" column="PATH" type="String" access="field" />
<property name="Checksum" column="CHECKSUM" type="String" access="field" />
<property name="Encrypted" column="ENCRYPTED" type="Boolean" access="field" />
<one-to-one name="Data" class="Pix.Data.Data, Pix.Data"
constrained="true" access="field" />
</class>
</hibernate-mapping>

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
<class name="Pix.Data.Data, Pix.Data" table="PICTURE">
<id name="Id" column="ID" type="Int32" unsaved-value="0" access="field">
<generator class="foreign">
<param name="property">Owner</param>
</generator>
</id>
<property name="Bytes" column="IMAGE" type="BinaryBlob" access="field" />
<one-to-one name="Owner" class="Pix.Data.Picture, Pix.Data" access="field" />
</class>
</hibernate-mapping>

The question is whether these mappings are correct (please givme a hint if not). Next issue is how to commit an object...

ITransaction transaction = session.BeginTransaction();
try
{
Pix.Data.Picture item = new Pix.Data.Picture();
item.Data = new Pix.Data.Data();
// item.Data.Owner = item; // need this??
progress += (100M / ((string[])e.Argument).Length);
ctrlImportWorker.ReportProgress(Convert.ToInt32(progress));
item.Name = Path.GetFileName(path);
item.Path = Path.GetFullPath(path);
byte[] imageBuffer = LoadFile(path);
item.Data.Bytes = Encryption.CoDec.Encrypt(imageBuffer);
item.Checksum = Encryption.CoDec.Hash(imageBuffer);
imageBuffer = null;
session.Save(item);
transaction.Commit();
}
catch(HibernateException x)
{
transaction.Rollback();
}

I get following error: "not-null property referrences a null or transient value: Pix.Data.Picture.Data". What exactly means transient - not yet saved?

P.S. How to write posts with tabs in the text?

TIA

sergey · **Posted:** Wed Jan 11, 2006 6:34 am

transient = does not exist in the database, that is, not yet saved or already deleted

rolandz · **Posted:** Thu Jan 12, 2006 3:27 am

OK - I will try to explain my question a bit better...

I have classes as following (in my data layer):

Code:

class Picture
{
  public int Id = 0;
  public Data Data;
}

class Data
{
  public Picture Owner;
  public int Id = 0;
  public byte[] Bytes;
}

I have changed mapping a bit so now it looks like this:

Code:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
  <class name="Pix.Data.Picture, Pix.Data" table="OBJECT">
    <id name="Id" column="ID" type="Int32" unsaved-value="0"
          access="field">
      <generator class="foreign">
        <param name="property">Data</param>
      </generator>
    </id>
    <one-to-one name="Data" class="Pix.Data.Data, Pix.Data"
                       constrained="true" access="field" />
  </class>
</hibernate-mapping>

and

Code:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
  <class name="Pix.Data.Data, Pix.Data" table="PICTURE">
    <id name="Id" column="ID" type="Int32"
          unsaved-value="0"access="field">
      <generator class="sequence">
        <param name="sequence">OBJECT_ID_GEN</param>
      </generator>
    </id>
    <property name="Bytes" column="IMAGE" type="BinaryBlob"
                    access="field" />
    <one-to-one name="Owner" class="Pix.Data.Picture, Pix.Data"
                       access="field" />
  </class>
</hibernate-mapping>

And now I would like to store a picture in my database (Firebird). So I assume I need to follow this:

Code:

void SavePicture(byte[] bytes, ISession sess)
{
  ITransaction tr = sess.BeginTransaction();
  try
  {
    Picture pic = new Picture();
    pic.Data = new Data();
    pic.Data.Bytes = bytes;
    sess.Save(pic);
    tr.Commit();
  }
  catch(HibernateException)
  {
    tr.Rollback();
  }
}

And now I wanted to ask my question... but decided to test it before. And finally I discoverred it works this way (did not with previous mapping).

So I also decided not to abandon this post. If it could be helpfull to anyone then I think it is worth to put it anyway. At least I did not find any hints in existing furum archive...

rolandz · **Posted:** Thu Jan 12, 2006 4:10 am

Now I added lazy initialization to Data class:

Code:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
  <class name="Pix.Data.Data, Pix.Data" table="PICTURE" lazy="true">
    <id name="Id" column="ID" type="Int32"
          unsaved-value="0"access="field">
      <generator class="sequence">
        <param name="sequence">OBJECT_ID_GEN</param>
      </generator>
    </id>
    <property name="Bytes" column="IMAGE" type="BinaryBlob"
                    access="field" />
    <one-to-one name="Owner" class="Pix.Data.Picture, Pix.Data"
                       access="field" />
  </class>
</hibernate-mapping>

Great... But now when I read my stored Picture object, I do NOT have Data field being initialized. Can anyone explain it to me? Does the generic proxy implementation in NHibernate (it is Castle, isn't i?) work with fields? If it does then why just simple invokation:

Code:

void Read(ISession sess, int id)
{
  Picture pic = (Picture)sess.Load(typeof(Picture), id);
  ShowPicture(pic.Data.Bytes);
}

doesn't work? The Data property has been initialized (I see it is just the proxy), but the data in it is NOT. Owner is null, id is zero, Bytes is null.

When I don't use lazy loading then it works :|

TIA