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 Post subject: Using the many-to-one mapping to return just a few fields
PostPosted: Wed May 09, 2012 6:48 pm 
Newbie

Joined: Wed May 09, 2012 6:24 pm
Posts: 2
Hi i could use some help here. I'm using Hibernate to integrate with a Payments and Payees table.
The Payee table has alot of columns and i need them all the mapped to the Payee object. Check.
But when i populate the Payments object i only want Payee's moreStuff field ( b/c i will be serializing the Payment object later on and don't want all the bulk )
So i feel like i need the many-to-one mapping. But i need something to specify that i just want the moreStuff String field not the tonsOfStuff field(s).
Does this make sense? Is there a way to do this with Hibernate?

Code:
<hibernate-mapping package="com.something">
    <class name="Payment" table="Payments" schema="dbo" catalog="APX2000">
        <id name="paymentId" type="int">
            <column name="paymentId" />
            <generator class="native" />
        </id>
        <property name="stuff" type="string">
            <column name="stuff" />
        </property>       
        <many-to-one name="payee" class="Payee" fetch="select" access="property">
            <column name="payeeId" />
        </many-to-one>
    </class>
</hibernate-mapping>

<hibernate-mapping package="com.something">
    <class name="Payee" table="Payees" schema="dbo" catalog="APX2000">
        <id name="payeeId" type="int">
            <column name="payeeId" />
            <generator class="native" />
        </id>
        <property name="moreStuff" type="string">
            <column name="moreStuff" />
        </property>
        <property name="tonsOfStuff" type="string">
            <column name="tonsOfStuff" />
        </property>
    </class>
</hibernate-mapping>

And here's the database schema:
Code:
CREATE TABLE Payments
(
   paymentId int IDENTITY(1,1) NOT NULL PRIMARY KEY,
   stuff varchar(20),
   payeeId int FOREIGN KEY REFERENCES Payees(payeeId),
)

CREATE TABLE Payees
(
   payeeId int IDENTITY(1,1) NOT NULL PRIMARY KEY,
   moreStuff varchar(20),
   tonsOfStuff varchar(20),
)


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 Post subject: Re: Using the many-to-one mapping to return just a few fields
PostPosted: Thu May 10, 2012 3:42 pm 
Newbie

Joined: Wed May 09, 2012 6:24 pm
Posts: 2
I have been unsuccessful. I tried this in the Payment mapping file:
Code:
       
<join table="Payees">
           <key column="payeeId"/>
           <property name="moreStuff" column="moreStuff"/>
</join>

But it didn't work. So i tried the @SecondaryTables Annotations syntax.
But i got an error saying this only works if you are doing a JOIN between two primary keys.
Now thats weird, its very common in the SQL universe to do a join on a Foreign key to a Primary Key. Perhaps i'm missing something.

Its pretty important for performance to control the fields returned on a JOIN. Returning all of them every time ( i.e. instantiating the whole Class on a many-to-one or one-to-one mapping ) seems very wasteful. Thoughts? Disagreements?


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