I'm inexperienced with sql in general, so using Hibernate is like looking for an answer before I know exactly what the question is. Please feel free to correct any misunderstandings I have. I am on a project where I have to use Hibernate. Most of what I am doing is pretty basic and I could copy and modify.
Now I would like to do something different and I'm not sure how configuration and syntax need to come together. Let's say I have two tables.
Table A has two (relevant) columns, user GUID and manager GUID. Obviously managers can have more than one user under them, so queries on manager can return more than one row. Additionally, a manager can be managing the same user on multiple projects, so the same user can be returned multiple times for the same manager query.
Table B has two columns, user GUID and user full name. One-to-one mapping there.
I want to do a query on manager GUID from Table A, group them by unique User GUID (so the same User isn'
t in the results twice), then return those users' full names from Table B.
I could do this in sql without too much trouble but I want to use Hibernate so I don'
t have to parse the sql results by hand. That's one of the points of using Hibernate, isn'
t it?
Right now I have Hibernate mappings that map each column in Table A to a field (well the get/set methods I guess) in a DAO object that I wrote just to hold that Table's data.
I could also use the Hibernate DAOs I have to access each table separately and do each of the things I mentioned above in separate steps, but that would be less efficient (I assume) that doing one query.
I wrote a Service object to hold the data that gets returned from the query (my example is simplified - I'm going to keep some other data from Table A and get multiple columns from Table B) but I'm at a loss for how to write a DAO that can do the join, or use the DAOs I have to do the join.
FYI, here is a sample of my hibernate config file (simplified to match my example):
<hibernate-mapping package="com.my.dao">
<class name="TableA" table="table_a">
<id name="pkIndex" column="pk_index" />
<property name="userGuid" column="user_guid" />
<property name="managerGuid" column="manager_guid" />
</class>
</hibernate-mapping>
So then I have a DAOImplementation class that does queries and returns lists like
public List<TableA> findByHQL(String hql, Map<String, String> params)
etc. I'm not sure how "best practice" that is either.
