inverse = “true” example and explanation

In Hibernate, only the “relationship owner” should maintain the relationship, and the “inverse” keyword is created to defines which side is the owner to maintain the relationship. However the “inverse” keyword itself is not verbose enough, I would suggest change the keyword to “relationship_owner“.

In short, inverse=”true” means this is the relationship owner, and inverse=”false” (default) means it’s not.
1. One to many Relationship
This is a one-to-many relationship table design, a STOCK table has many occurrences in STOCK_DAILY_RECORD table.
2. Hibernate Implementation

See the Hibernate implementation in XML mapping files.

File : Stock.java

public class Stock implements java.io.Serializable {
   ...
   private Set<StockDailyRecord> stockDailyRecords =
new HashSet<StockDailyRecord>(0);
   ...

File : StockDailyRecord.java

public class StockDailyRecord implements java.io.Serializable {
   ...
   private Stock stock;
   ...

File : Stock.hbm.xml

<hibernate-mapping>
    <class name="com.mkyong.common.Stock" table="stock" ...>
    ...
    <set name="stockDailyRecords" table="stock_daily_record" fetch="select">
        <key>
            <column name="STOCK_ID" not-null="true" />
        </key>
        <one-to-many class="com.mkyong.common.StockDailyRecord" />
    </set>
    ...

File : StockDailyRecord.hbm.xml

<hibernate-mapping>
  <class name="com.mkyong.common.StockDailyRecord" table="stock_daily_record" ...>
  ...
  <many-to-one name="stock" class="com.mkyong.common.Stock">
       <column name="STOCK_ID" not-null="true" />
  </many-to-one>
  ...

3. inverse = true / false

Inverse keyword is applied in one to many relationship. Here’s the question, if save or update operation perform in “Stock” object, should it update the “stockDailyRecords” relationship?

File : Stock.hbm.xml

    <class name="com.mkyong.common.Stock" table="stock" ...>
    ...
    <set name="stockDailyRecords" table="stock_daily_record" inverse="{true/false}" fetch="select">
        <key>
            <column name="STOCK_ID" not-null="true" />
        </key>
        <one-to-many class="com.mkyong.common.StockDailyRecord" />
    </set>
    ...

1. inverse=”true”

If inverse=”true” in the set variable, it means “stock_daily_record” is the relationship owner, so Stock will NOT UPDATE the relationship.

<class name="com.mkyong.common.Stock" table="stock" ...>
    ...
<set name="stockDailyRecords" table="stock_daily_record" inverse="true" >

2. inverse=”false”

If inverse=”false” (default) in the set variable, it means “stock” is the relationship owner, and Stock will UPDATE the relationship.

<class name="com.mkyong.common.Stock" table="stock" ...>
...
<set name="stockDailyRecords" table="stock_daily_record" inverse="false" >

See more examples below :
4. inverse=”false” Example

If keyword “inverse” is not define, the inverse = “false” will be used, which is

<!--Stock.hbm.xml-->
<class name="com.mkyong.common.Stock" table="stock" ...>
...
<set name="stockDailyRecords" table="stock_daily_record" inverse="false">

It means “stock” is the relationship owner, and it will maintains the relationship.

Insert example …

When a “Stock” object is saved, Hibernate will generated three SQL statements, two inserts and one update.

    session.beginTransaction();

    Stock stock = new Stock();
    stock.setStockCode("7052");
    stock.setStockName("PADINI");

    StockDailyRecord stockDailyRecords = new StockDailyRecord();
    stockDailyRecords.setPriceOpen(new Float("1.2"));
    stockDailyRecords.setPriceClose(new Float("1.1"));
    stockDailyRecords.setPriceChange(new Float("10.0"));
    stockDailyRecords.setVolume(3000000L);
    stockDailyRecords.setDate(new Date());

    stockDailyRecords.setStock(stock);       
    stock.getStockDailyRecords().add(stockDailyRecords);

    session.save(stock);
    session.save(stockDailyRecords);

    session.getTransaction().commit();

Output…

Hibernate:
    INSERT
    INTO
        mkyongdb.stock
        (STOCK_CODE, STOCK_NAME)
    VALUES
        (?, ?)
Hibernate:
    INSERT
    INTO
        mkyongdb.stock_daily_record
        (STOCK_ID, PRICE_OPEN, PRICE_CLOSE, PRICE_CHANGE, VOLUME, DATE)
    VALUES
        (?, ?, ?, ?, ?, ?)
Hibernate:
    UPDATE
        mkyongdb.stock_daily_record
    SET
        STOCK_ID=?
    WHERE
        RECORD_ID=?

Stock will update the “stock_daily_record.STOCK_ID” through Set variable (stockDailyRecords), because Stock is the relationship owner.
Note
The third statement is really NOT necessary.

Update example …

When a “Stock” object is updated, Hibernate will generated two SQL statements, one inserts and one update.

    session.beginTransaction();

    Stock stock = (Stock)session.get(Stock.class, 57);

    StockDailyRecord stockDailyRecords = new StockDailyRecord();
    stockDailyRecords.setPriceOpen(new Float("1.2"));
    stockDailyRecords.setPriceClose(new Float("1.1"));
    stockDailyRecords.setPriceChange(new Float("10.0"));
    stockDailyRecords.setVolume(3000000L);
    stockDailyRecords.setDate(new Date());

    stockDailyRecords.setStock(stock);       
    stock.getStockDailyRecords().add(stockDailyRecords);

    session.save(stockDailyRecords);
    session.update(stock);

    session.getTransaction().commit();

Output…

Hibernate:
    INSERT
    INTO
        mkyongdb.stock_daily_record
        (STOCK_ID, PRICE_OPEN, PRICE_CLOSE, PRICE_CHANGE, VOLUME, DATE)
    VALUES
        (?, ?, ?, ?, ?, ?)
Hibernate:
    UPDATE
        mkyongdb.stock_daily_record
    SET
        STOCK_ID=?
    WHERE
        RECORD_ID=?

Note
Again, the third statement is NOT necessary.
5. inverse=”true” Example

If keyword “inverse=true” is defined :

<!--Stock.hbm.xml-->
<class name="com.mkyong.common.Stock" table="stock" ...>
...
<set name="stockDailyRecords" table="stock_daily_record" inverse="true">

Now, it means “stockDailyRecords” is the relationship owner, and “stock” will not maintains the relationship.

Insert example …

When a “Stock” object is saved, Hibernate will generated two SQL insert statements.

    session.beginTransaction();

    Stock stock = new Stock();
    stock.setStockCode("7052");
    stock.setStockName("PADINI");

    StockDailyRecord stockDailyRecords = new StockDailyRecord();
    stockDailyRecords.setPriceOpen(new Float("1.2"));
    stockDailyRecords.setPriceClose(new Float("1.1"));
    stockDailyRecords.setPriceChange(new Float("10.0"));
    stockDailyRecords.setVolume(3000000L);
    stockDailyRecords.setDate(new Date());

    stockDailyRecords.setStock(stock);       
    stock.getStockDailyRecords().add(stockDailyRecords);

    session.save(stock);
    session.save(stockDailyRecords);

    session.getTransaction().commit();

Output …

Hibernate:
    INSERT
    INTO
        mkyongdb.stock
        (STOCK_CODE, STOCK_NAME)
    VALUES
        (?, ?)
Hibernate:
    INSERT
    INTO
        mkyongdb.stock_daily_record
        (STOCK_ID, PRICE_OPEN, PRICE_CLOSE, PRICE_CHANGE, VOLUME, DATE)
    VALUES
        (?, ?, ?, ?, ?, ?)

Update example …

When a “Stock” object is updated, Hibernate will generated one SQL statement.

    session.beginTransaction();

    Stock stock = (Stock)session.get(Stock.class, 57);

    StockDailyRecord stockDailyRecords = new StockDailyRecord();
    stockDailyRecords.setPriceOpen(new Float("1.2"));
    stockDailyRecords.setPriceClose(new Float("1.1"));
    stockDailyRecords.setPriceChange(new Float("10.0"));
    stockDailyRecords.setVolume(3000000L);
    stockDailyRecords.setDate(new Date());

    stockDailyRecords.setStock(stock);       
    stock.getStockDailyRecords().add(stockDailyRecords);

    session.save(stockDailyRecords);
    session.update(stock);

    session.getTransaction().commit();

Output…

Hibernate:
    INSERT
    INTO
        mkyongdb.stock_daily_record
        (STOCK_ID, PRICE_OPEN, PRICE_CLOSE, PRICE_CHANGE, VOLUME, DATE)
    VALUES
        (?, ?, ?, ?, ?, ?)