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sign
 Post subject: 1 class, 2 tables, some conditions... mapping.
PostPosted: Wed Jun 13, 2007 5:28 am 
Newbie

Joined: Wed Jun 13, 2007 4:50 am
Posts: 4
hi there.
im new to hibernate. i really cant figure out how can i map one class to two tables with no direct relation (FK<->PK).


i have this 2 tables:

Stops:
-code
-thing
...

Problems:
-code
-description



and this sql statment:

SELECT S.code, P.description, thing, ...
FROM Stops S, Problems P
WHERE S.code=P.code AND thing<>'sausages'
ORDER BY code DESC


i want each line of the resulting table of this SQL to be represented by one object of my class. is there a way?
i know i can use the join element to bring together columns from diferent tables,
but how can i express the conditions in the hibernate mapping file???


many thanks in advance.
hope anyone can help me.
cheers
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sign
 Post subject:
PostPosted: Wed Jun 13, 2007 6:53 am 
Newbie

Joined: Wed Jun 13, 2007 4:50 am
Posts: 4
i forgot something in the Stops database table:

Stops:
-stopid <-----
-code
-thing
...

can anyone tell me if this mapping will do the trick???


Code:
<hibernate-mapping>

   <class name="package.Stop" table="Stops"
      where="Stops.code=Problems.code AND NOT(thing='sausages')">

      <id name="stopid">
         <generator class="assigned" />
      </id>

      <property name="code" />
      <property name="thing" />

      
      <join table="Problems">
         <key column="code"/>
         <property name="description" />
      </join>


   </class>

</hibernate-mapping>



and if i dont want to map the 'stopid' column of the table? i do need to define another <id> element for the class, right?

many thanks
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jits_1998
 Post subject: Re:
PostPosted: Wed Jun 13, 2007 7:36 am 
Senior
Senior

Joined: Tue Jun 12, 2007 4:49 pm
Posts: 127
Location: India
Hi sign,

Hibernate does not recomend this approach but it does support this kind of requirement for legacy systems.

You need to create a unique key on the first class with the two columns which are being referred in the second table.

Then in the second class you would need to use property-ref to the unique key on the first class.

Let me know if you need more detailed solution. If you do give me your hibernate mapping files and I will update them.

Regards,
Jitendra
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sign
 Post subject:
PostPosted: Wed Jun 13, 2007 9:07 am 
Newbie

Joined: Wed Jun 13, 2007 4:50 am
Posts: 4
That is my case, a legacy system... cant change database.

(Correction: there is a PK-FK relationship between the tables, sorry)

Stops:
- stopID NOTNULL primarykey
- code NOTNULL foreignkey
- thingA NOTNULL
- thingB NOTNULL
- othersThings

Problems:
- code NOTNULL primarykey
- description
- thing1 NOTNULL
- thing2 NOTNULL


i want to map a class like:

Code:
package testPackage;

public class Stop {
   private String code;
   private String thingA;
   private String thingB;
   private String otherThings;
   private String description;

   ...

   //gets and sets

}

the only thing coming from the 'Problems' table is the 'description' that matches the 'code'.
in my case i only want to read this information from the database, never updates, inserts...etc.
do i need to map the stopID too?

Quote:
"You need to create a unique key on the first class with the two columns which are being referred in the second table."

can you show me a example?
Quote:
"Then in the second class you would need to use property-ref to the unique key on the first class. "

can this be done with only one class like the one above?

thanks.
Andre
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jits_1998
 Post subject:
PostPosted: Wed Jun 13, 2007 2:12 pm 
Senior
Senior

Joined: Tue Jun 12, 2007 4:49 pm
Posts: 127
Location: India
Unless the primary key in both the tables is same I don't think its possible to do it using a single class.

Any issues with having 2 classes? One of them could be an internal class...

sample for unique-key ..
Code:
<property name="x">
         <column name="xval" not-null="true" length="4" unique-key="xy"/>
      </property>
      <property name="y">
         <column name="yval" not-null="true" length="4" unique-key="xy"/>
      </property>


But since you have a FK relationship the unique-key and property-ref is not required in your case.

Regards,
Jitendra
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sign
 Post subject:
PostPosted: Thu Jun 14, 2007 5:38 am 
Newbie

Joined: Wed Jun 13, 2007 4:50 am
Posts: 4
hi... i've came up with something that might result well... i think.

THE TALES are has shown above.

THE CLASSES:

Code:
public class Stop {
   private Integer stopid;
   private String thinga;
   private String thingb;
   private Problem prob;
//gets-sets
...
}

public class Problem {
   private String code;
   private String description;
   private String thinga;
   private String thingb;
//gets-sets
...
}


THE MAPPING FILES:

Code:
<!--  STOP -->
<hibernate-mapping>

   <class name="hib.test.Stop" table="Stops" where="NOT (thinga='sausages')">
   
      <id name="stopid">
         <generator class="assigned"/>
      </id>      
      <many-to-one name="prob" class="hib.test.Problem" column="code"/>      
      <property name="thinga"/>      
      <property name="thingb"/>

   </class>

</hibernate-mapping>

<!--  PROBLEM -->
<hibernate-mapping>

   <class name="hib.test.Problem" table="Problems">
   
      <id name="code">
         <generator class="assigned"/>
      </id>      
      <property name="description"/>   
      <property name="thing1"/>      
      <property name="thing2"/>   

   </class>

</hibernate-mapping>



the only problem is this way im getting all the information, all the columns and not only the ones i need. since i'm not going to change the database data, only reading data, could i ignore the primary key column of the stops table (stopid) and some other columns and shrink the class to:

Code:
public class Stop {
   private String thinga;
   private Problem prob;
//gets-sets
...
}


and how could the hibernate mapping be to map this?
or maybe mapping only the NOTNULL fields :?


thanks a lot
cheers

André
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jits_1998
 Post subject: Re:
PostPosted: Thu Jun 14, 2007 6:54 am 
Senior
Senior

Joined: Tue Jun 12, 2007 4:49 pm
Posts: 127
Location: India
All columns except primary key can be skipped. If there is any other column that is unique, then you can use that as your id column.

Regards,
Jitendra
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