Hibernate Mapping

Question

I am new to hibernate and trying to understand it. I have below tables :-

We have session_tbl table as below :-

Session_ID | Creation_Time  
1          | 23-Mar-2014
2          | 24-Mar-2014
3          | 25-Mar-2014
4          | 26-Mar-2014


and stock_tbl as below :- 

Stock_id   | price   | session_id
1          | 11.00   | 1
2          | 12.00   | 1
3          | 43.00   | 1
4          | 51.00   | 2
5          | 85.00   | 4
6          | 61.00   | 3
7          | 66.00   | 2
8          | 81.00   | 1

in above session_id is using as foreign key for session_tbl.

In hibernate how can we specify mapping in xml file ? I want to fetch stock_tbl data only, i will never query session_tbl to get stock.

We need Session_tbl object need to be created in Stock_tbl class. But no Stock_tbl object with Session_tbl class.

We want to use session_tbl for tracking purpose we have more then 100 table which are having session_tbl as foreign key in all the table. in this case we have to put Set for all the classes in Session_tbl unnecessary. As we want session details only from Stock_tbl and same with all remain 99 tables (when required fetch session_tbl - lazy loading).

I have created mapping as below :-

public class Session_tbl {
   private int session_id;
   private String dateTime; 
   private Set<Stock_tbl> stockTbl;
   // Question 1 


.. Getter and Setter
}

public class Stock_tbl{
   private int stock_id;
   private Session_tbl sessionTbl;
   private int price; 

.. Getter and Setter
}

<class name="Session_tbl" table="session_tbl">

      <id name="session_id" type="int" column="session_id">
         <generator class="native"/>
      </id>
      <set name="stockTbl" cascade="all">
         <key column="stock_id"/>
         <one-to-many class="Stock_tbl"/>
      </set>
      // Question 2
......

</Class>

<class name="Stock_tbl" table="stock_tbl">

      <id name="stock_id" type="int" column="stock_id">
         <generator class="native"/>
      </id>
      ....
   </class>

Question:

1. Why do i need to use set in Session_tbl class because i dont want to fetch stock from here? i need only Session_tbl Object in below class.

2. Why this mapping needed in Sesison_tbl table? for all the 100 classes do i have to create there mapping here?

Answer 1

You define only the ManyToOne part of the relationship in your Stock_tbl class. You don't need to add anything to the Session_tbl class, or any other of your 100 classes if they don't want to use their relationsip to the Session.

<class name="Stock_tbl" table="stock_tbl">

      <id name="stock_id" type="int" column="stock_id">
         <generator class="native"/>
      </id>
      <many-to-one name="sessionTbl" column="session_id" class="Session_tbl" not-null="true"/>
      ....
</class>
<class name="Session_tbl" table="session_tbl">

      <id name="session_id" type="int" column="session_id">
         <generator class="native"/>
      </id>
      //remove the stockTbl field from the Session class
</Class>

With anotation (recommended instead of xml as the mappings is next to your code), it simply looks like that:

@Entity
public class Stock_tbl{
   @Id
   @GeneratedValue(strategy = GenerationType.AUTO)
   private int stock_id;
   @ManyToOne
   @JoinColumn(name="session_id")
   private Session_tbl sessionTbl;
   private int price; 

.. Getter and Setter
}

@Entity
public class Session_tbl {
   @GeneratedValue(strategy = GenerationType.AUTO)
   private int session_id;
   private String dateTime; 
   //remove the stock if you dont want to use it
.. Getter and Setter
}

Unless you meant that you really don't want to have the Session class at all. Then you don't provide any Session_tbl mapping. Inside your Stock_tbl you defined just the column for session_id, and you will need to handle it yourself (ie. set the correct sessionId value).

@Entity
public class Stock_tbl{
   @Id
   @GeneratedValue(strategy = GenerationType.AUTO)
   private int stock_id;

   private int session_id; //now it is a simple id, not relationships/objectc
   private int price; 
.. Getter and Setter
}