Easy retrieval of child records

steinrr · **Joined:** Tue Mar 13, 2007 9:46 am **Posts:** 20

I am a Hibernate beginner and have a really simple case, that I can not seem to find the solution to. I have searched tutorials and references, but I must have missed something.

I have a table "header_table" that is a parent table. I also have a "line_table" that are child records of the "header_table" (one-to-many) - one header-record can have multiple line-records. The column linking these two tables are header_id

What I want to do is to retrieve one header_table-record together with all line_table-records for that record.

Can someone help me with:

* What to put in the mapping files
* What to put in the java-files of header_table.java and line_table.java
* Some simple lines of testcode for retrieving this

I've tried so many different things, and nothing works. It only seems to load the header_table...

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

Assuming that lines have line numbers, the mapping in your <class name="Header" ...> is

Code:

<list name="lines">
  <key="header_id"/>
  <index column="line_number"/>
  <one-to-many class="Line"/>
</list>

And you'll need this in your Lines class' mapping:

Code:

<many-to-one name="header" class="Header" column="header_id"/>

You'll need the appropriate properties in the two classes, too. Headers needs a "List<Line> getLines()" and "void setLines(List<Line> lines)" (never call the set method, it's just for hibernate), and it should have a default value (private List<Line> m_lines = new ArrayList<Line>();). Lines needs "Header getHeader()" and "void setHeader(Header header)"..

steinrr · **Joined:** Tue Mar 13, 2007 9:46 am **Posts:** 20

Thanks for your answer. What Java code do I write to make Hibernate perform the query?

will .getLines() force a SQL query?

Stein Rune

damnhandy · **Posted:** Sat Apr 14, 2007 10:10 pm

Yes, it will execute a SQL query if the collection has not been loaded and if the code is being executed within an active transaction. If there is not transaction, a LazyInitializationException will be thrown.

Ryan-