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How can I do this mapping:

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fabricio.lemos

Post subject: How can I do this mapping:

Posted: Fri Dec 02, 2005 2:26 pm

Newbie

Joined: Fri Dec 02, 2005 8:03 am
Posts: 10

I´m looking for a way of doing the mapping for this relationship:

A Document entity has a reference for a File entity. The relationship is an unidirectional composition:a Document has 0 or 1 File and a File always belongs to one and only one Document. In the data base I have the Document table and the File table. The File table has the column “documentID” which is a foreign key that references the table Document.
How could I map this relationship in the Document hbm?

thanks in advance,
Fabrício Lemos

Hibernate version: 3.0.5

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anandbn

Post subject:

Posted: Fri Dec 02, 2005 11:56 pm

Regular

Joined: Wed May 05, 2004 3:41 pm
Posts: 118
Location: New Jersey,USA

Here's something that might work for your requirement:

Mapping for Document

Code:

<hibernate-mapping>
    <class name="com.hibernate.forums.Document" 
           table="Document"
           >
        <id name="documentId" type="integer">
            <column name="documentId" />
            <generator class="assigned" />
        </id>           
      <set    name="fileList"
            cascade="all-delete-orphan"
            inverse="true"
            lazy="true"
            access="field"
            outer-join="true">
           <key>
               <column name="documentId" not-null="true"/>
           </key>
           <one-to-many class="com.hibernate.forums.File"/>
      </set>           
    </class>
</hibernate-mapping>

Mapping for File

Code:

<hibernate-mapping>
   <class name="com.hibernate.forums.File" 
           table="File">
        <id name="fileId" type="integer">
            <column name="fileId" />
            <generator class="assigned" />
        </id>
        <property name="description" type="string">
            <column name="description"/>
        </property>   
    </class>
</hibernate-mapping>

You can look at:

http://forum.hibernate.org/viewtopic.ph ... highlight=

You can also look:
http://caveatemptor.hibernate.org
[/u][/b]

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fabricio.lemos

Post subject: Document has 0 or 1 File, and not a collection of then.

Posted: Sat Dec 03, 2005 1:36 am

Newbie

Joined: Fri Dec 02, 2005 8:03 am
Posts: 10

In Document class I have:

Code:

class Document{
  private File file;
//... get and set methods
}

not:

Code:

class Document{
 private List fileList;
//...get and set methods
}

Document has 0 or 1 File, not a collection of then.
So I don´t thing that the <set> mapping in document .hbm might work.

thanks anyway...

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anandbn

Post subject:

Posted: Sat Dec 03, 2005 11:09 am

Regular

Joined: Wed May 05, 2004 3:41 pm
Posts: 118
Location: New Jersey,USA

I don't think you have a <one-or-zero> kind of mapping in Hibernate. Typically this is considered as a special case of <one-to-many> were the many is 0 or 1.

You could however still have "setFile" and getFile but use a Set in the implementation. Something like this:

Code:

public File getFile(){
   if(this.fileList != null && ! this.fileList.isEmpty()){
     return (File)fileList.get(0);
   }else{ 
     return null;
   }
}

You could also change the "access" mode to "field" in the HBM. This i think would then not require any "setters/getters" like getFileList(), setFileList(), there by not exposing more method than what you want.

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puffybsd

Post subject:

Posted: Sat Dec 03, 2005 10:44 pm

Regular

Joined: Mon Sep 29, 2003 9:39 am
Posts: 67

one-to-one is what you want to use. For the case where object A doesn't have a B, A.getB() is null. There would be no corresponding row for B in this case. Manage the relationship using cascades.

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fabricio.lemos

Post subject:

Posted: Mon Dec 05, 2005 8:54 am

Newbie

Joined: Fri Dec 02, 2005 8:03 am
Posts: 10

anandbn wrote:

I don't think you have a <one-or-zero> kind of mapping in Hibernate. Typically this is considered as a special case of <one-to-many> were the many is 0 or 1.

I´m sorry to hear that. This is a so common kind of relationship, that I thought hibernate would offer support.
Thanks for the answer.

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fabricio.lemos

Post subject:

Posted: Mon Dec 05, 2005 8:57 am

Newbie

Joined: Fri Dec 02, 2005 8:03 am
Posts: 10

puffybsd wrote:

one-to-one is what you want to use. For the case where object A doesn't have a B, A.getB() is null. There would be no corresponding row for B in this case. Manage the relationship using cascades.

I can´t even start writing the .hbm mapping for this relationship.

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puffybsd

Post subject:

Posted: Sat Dec 10, 2005 4:26 pm

Regular

Joined: Mon Sep 29, 2003 9:39 am
Posts: 67

Here's some help:

Code:

<class name="Document">
  <one-to-one name="folder"/>
</class>
<class name="Folder">
  <id name="id" column="document_id">
    <generator class="foreign">
      <param property="document"/>
    </generator>
  </id>
  <one-to-one name="document" class="Document" constrained="true" />
</class>

If you are not already using XDoclet's hibernatedoclet, you really need to check it out. It's much easier to keep your source and mappings synchronized.

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fabricio.lemos

Post subject: The relationship is unidirectional.

Posted: Mon Dec 12, 2005 7:59 am

Newbie

Joined: Fri Dec 02, 2005 8:03 am
Posts: 10

The relationship is unidirectional: in File class I don´t have a reference to the Document class. Is Document that has a reference to File class. So, I don´t think I can put the
<one-to-one name="document" class="Document" constrained="true" /> tag at the File hbm.

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