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How to get the null element back?

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JavaRanch

Post subject: How to get the null element back?

Posted: Tue Jun 20, 2006 3:22 am

Newbie

Joined: Tue Jun 20, 2006 3:09 am
Posts: 4

I can put a null element into a set and it is successfully persisted into the database. But after I retrieve it back, the null element is gone.

How to get the null element back?

Hers is the map file( the set contains all the addresses a person has.):

Code:

      
<class name="user.UserInfo" table="user_info">
        <id name="id" type="int">
            <column name="id" />
         <generator class="native"/>
        </id>

        ...

        <set name="addresses" table="User_Addr" inverse="false" cascade="all" lazy="true">
         <key column="userId"/>
         <element column="address" type="string" not-null="false"/>
        </set>
</class>

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JavaRanch

Post subject:

Posted: Tue Jun 20, 2006 7:24 pm

Newbie

Joined: Tue Jun 20, 2006 3:09 am
Posts: 4

Still waiting...
Thanks.

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VampBoy

Post subject:

Posted: Wed Jun 21, 2006 4:33 pm

Expert

Joined: Sat Jan 17, 2004 2:57 pm
Posts: 329
Location: In the basement in my underwear

You don't? What does a NULL address represent? The system isn't going to know that you want a NULL element in your set when it comes back from the DB.

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JavaRanch

Post subject:

Posted: Wed Jun 21, 2006 7:27 pm

Newbie

Joined: Tue Jun 20, 2006 3:09 am
Posts: 4

VampBoy wrote:

You don't? What does a NULL address represent? The system isn't going to know that you want a NULL element in your set when it comes back from the DB.

This is just an example illustrate that a NULL element can not be fetched back after it has been persisted. In real application, this is not address information but other information that null has a specifical meaning.

I also wonder that if it can not be retrieved back, why should hibernate persisted it into database.

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VampBoy

Post subject:

Posted: Wed Jun 21, 2006 7:29 pm

Expert

Joined: Sat Jan 17, 2004 2:57 pm
Posts: 329
Location: In the basement in my underwear

Out of curiousity, what is a NULL element persisted as in the DB? You're making it sound like it is actually saving a record?

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JavaRanch

Post subject:

Posted: Thu Jun 22, 2006 1:53 am

Newbie

Joined: Tue Jun 20, 2006 3:09 am
Posts: 4

VampBoy wrote:

Out of curiousity, what is a NULL element persisted as in the DB? You're making it sound like it is actually saving a record?

You don't know the null element in database?

null element(address field). NOT NULL record.

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RafaelPierre

Post subject: Re: How to get the null element back?

Posted: Thu Jun 22, 2006 7:45 am

Newbie

Joined: Thu May 04, 2006 4:44 am
Posts: 1

Code:

      
<class name="user.UserInfo" table="user_info">
        <id name="id" type="int">
            <column name="id" />
         <generator class="native"/>
        </id>

        ...

        <set name="addresses" table="User_Addr" inverse="false" cascade="all" lazy="true">
         <key column="userId"/>
         <element column="address" type="string" not-null="false"/>
        </set>
</class>

[/quote]

When writing your query you should make an outer join, something like this:
select adres
from User as user
left outer join user.adress as adress
where user.id = x

Read more about this LEFT OUTER JOIN

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