inverse = “true” example and explanation

Always put inverse=”true” in your collection variable ?
There are many Hibernate articles try to explain the “inverse” with many Hibernate “official” jargon, which is very hard to understand (at least to me). In few articles, they even suggested that just forget about what is “inverse”, and always put inverse=”true” in the collection variable.

This statement is always true – “put inverse=true in collection variable”, but do not blindfold on it, try to understand the reason behind is essential to optimal your Hibernate performance.

What is “inverse” ?

This is the most confusing keyword in Hibernate, at least i took quite a long time to understand it. The “inverse” keyword is always declare in one-to-many and many-to-many relationship (many-to-one doesn’t has inverse keyword), it means which side is responsible to take care of the relationship.

“inverse”, should change to “relationship owner”?

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.

one to many relationship

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
        (?, ?, ?, ?, ?, ?)
inverse vs cascade
Many people like to compare between inverse and cascade, but both are totally different notions, see the differential here.

Conclusion

Understanding the “inverse” is essential to optimize your Hibernate code, it helps to avoid many unnecessary update statements, like “insert and update example for inverse=false” above. At last, try to remember the inverse=”true” mean this is the relationship owner to handle the relationship.

Reference

  1. http://simoes.org/docs/hibernate-2.1/155.html
  2. http://docs.jboss.org/hibernate/stable/core/reference/en/html/example-parentchild.html
  3. http://tadtech.blogspot.com/2007/02/hibernate-when-is-inversetrue-and-when.html

About the Author

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mkyong
Founder of Mkyong.com, love Java and open source stuff. Follow him on Twitter. If you like my tutorials, consider make a donation to these charities.

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Vittorio Ballestra
Guest
Vittorio Ballestra

Probably it’s me, but I found this article very confusing. I appreciate your effort expetially for the SQL generated query part but IMHO your article can be improved. The main source of confusion comes from the part when you say that inverse should be renamed “relationship_owner” while it is clear that it is rather the opposite. It should be renamed “relationship_NOT_owner”. In one of your example you say that having “inverse=true” makes the Stock object not to update the other side of the relationship. Thus at the end of the day I find that “Inverse” is the correct name for… Read more »

dreamfly
Guest
dreamfly

Actually it’s from the Set’s perspective

The set stockDailyRecords is the owner

trackback
Hibernate – One-to-many relationship example | Hibernate

[…] The inverse=”true” is tells Hibernate about the relationship owner is belong to other side , not the class. More detail…. […]

trackback
Different between cascade and inverse | Hibernate

[…] Hibernate will only insert or update the STOCK table, no update on the foreign key column. More detail example here… […]

trackback
Hibernate – Many-to-many relationship example | Hibernate

[…] StockCategory maintain the relationship between Stock and Category, see inverse=”true” explanation. […]

trackback
Blog bookmarks 03/27/2010 « My Diigo bookmarks

[…] inverse = “true” example and explanation | Hibernate […]

trackback
Hibernate Tutorials | Tutorials

[…] inverse = “true” example and explanation The “inverse” is the most confusing keyword in Hibernate, but you have to understand this clearly in order to fine tune your relationship performance. […]

Sudhakar
Guest
Sudhakar

In the above example:

update the foreign key “stock_daily_record.ITEM_ID” in StockDailyRecord table–>

I am confused stock_daily_record.ITEM_ID means the Stock_Id(Foreign key) inthe stockDailyRecord table am i right..if not please clarify.

dima
Guest
dima

You have something completely wrong in your article:

However the “inverse” keyword itself is not verbose enough, I would suggest change the keyword to “relationship_owner”.

“inverse” attribute should be interpreted as “ignore relationship” or something like that, it seems that you’ve completely wrong here.

Mahesh S
Guest
Mahesh S

Yes I have gone through a site which explained it through the “ignore relationship”. May be the text of that site or something, I really couldn’t understand what he was trying to say. Here with the “relationship_owner” example I could very easy understand.

Thanks mkyong for this wonderful piece of information

Tim
Guest
Tim

OMG!!!!!! Thank you soooo much!!!! I have been pulling my hair out trying to get a set to persist! Hugs and Kisses!!! XXOOXXOOXXOO

Ram
Guest
Ram

Hi,

It is an excellent article…
I went through many articles but they could not explain the term so well. Now it is crystal clear…

Thanks!! a lot..

Amit
Guest
Amit

Nice Article explain an important concept. I use JPA 2.0 with hibernate as the underlying persistence provider. Can you tell me how to specify inverse=true using jpa/hibernate annotations.

rwruck
Guest
rwruck

See http://docs.jboss.org/hibernate/core/3.3/reference/en/html/associations.html#assoc-bidirectional

inverse=”true” means that THE OTHER side is the relationship owner and this one is just the inverse, so relationship_owner=”true” would be equal to inverse=”false”.

Since this post is among the first returned by Google when searching for “hibernate inverse” and since you already got it right here: http://www.mkyong.com/hibernate/hibernate-one-to-many-relationship-example/ – it would be nice if you could correct this.

trackback
Hibernate: inverse=true | javawithoutcoffee

[…] This article, currently the first result for “Hibernate inverse”, is misleading.  You don’t ALWAYS want to set inverse=true.  The Hibernate documentation does in fact state: If the foreign key column of a <one-to-many> association is declared NOT NULL, you must declare the <key> mapping not-null="true" or use a bidirectional association with the collection mapping marked inverse="true". See Section 7.3.2, “Bidirectional associations”. […]

Ajith
Guest
Ajith

excellent writeup esp since u explained what will happen if inverse=false. i was thinking if i dont specify inverse=true then hibernate will give error or do a wrong update.keep it up.

Anish Patel
Guest
Anish Patel

Hi,

It is nice explanation, however after reading this: it seems to me what’s the use of inverse=false then!!! As it’s create an extra update statement, why Hibernate core lib set inverse=true instead of default false?

Thanks,
Anish

Deb Singh
Guest
Deb Singh

I’m not sure, why this article making inverse so complicated to understand. JBoss web site clearly mentioned that in one-2-many, inverse = true has to be at many side, and in many-2-many, it does not matter which side you put. Following is excerpt from the site.

=========================================================
The rules are straightforward: all bi-directional associations need one side as inverse. In a one-to-many association it has to be the many-side, and in many-to-many association you can select either side.
=========================================================

evilkyro1965
Guest
evilkyro1965

Great article, thanx

trackback
Inverse Relationship In Hibernate And JPA « Amit's Tech Blog

[…] good links explaining this concept can be found here, here and […]

Fernando
Guest
Fernando

Clear and simple explanation Thanks! Sometimes the “oficial” documentation is not as clear as we would like.

rguntu
Guest
rguntu

VeryGood Explanation.

Priyatham
Guest
Priyatham

I have a confusion. This is what I understand from your article – If inverse=true, an insert on stock will trigger 2 inserts. First insert is on the stock record and the second one on the stockDailyRecord. But since in your code, you have taken care of the relationship using java. What I mean is you have set the stock object to the stockDailyRecord (in this line…stockDailyRecords.setStock(stock); ). This tells me that after 2 inserts, the relationship is actually present in the DB..i.e, the foreign key in the stockDailyRecord will actually have a value (the id of the stock record).… Read more »

krishnamurthy
Guest
krishnamurthy

Nice Example…………….

Vivek K
Guest
Vivek K

Hi,

Very simple and clear example. Great article, Thanks!

Can you please provide an example where to use inverse=false?

Thanks in advance..

Aslam
Guest
Aslam

Hi, Good article Indeed. But I have a doubt, In Hibernate using annotation how to provide “inverse=true”

Anuradha
Guest
Anuradha

Hi,

Thanks, it helped a lot…

Chandraprakash Sarathe
Guest
Chandraprakash Sarathe

Thanks for this article which is descriptive and at the same time informative.

pinky
Guest
pinky

how to annotate classes for same example

pinky
Guest
pinky

how to use annotations to define inverse=”true” ?

Abu
Guest
Abu

Nice example!

Biswaa
Guest
Biswaa

so nice Example..
now it is very clear to me..
thanx a lot..