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

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

Comments

Leave a Reply

avatar
newest oldest most voted
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

dreamfly
Guest
dreamfly

clearest explanation I read.

Naveen
Guest
Naveen

Can you please explain, if inverse=false, and if stock_id inside stock_daily_record is a not null record then how will this work.

Do we not get an error while executing insert into stock_daily_record?

Nikhil
Guest
Nikhil

Hi, where is the update query for stock object in both update examples.

Keerti
Guest
Keerti

thanks for the post

sudhanshoo vashisht
Guest
sudhanshoo vashisht

ya it is awsome explation…but can we used inverse with list tag..m trying but seq column return null value

Prateek Ashtikar
Guest
Prateek Ashtikar

I don’t see link to download source code. Could you please make it available?

Philip Jahmani Chauvet
Guest
Philip Jahmani Chauvet

Awesome! What a confusing topic “inverse”. Eventually, I got tired of figuring it out myself, and tried this and that. You my man, provided a great example.

Good work.

Farhan Ansar
Guest
Farhan Ansar

For your case 4. inverse=”false” Example

When a “Stock” object is saved, Hibernate will generated three SQL statements, two inserts and one update.
Then, you mention:
Note
Again, the third statement is NOT necessary.

stockDailyRecords.setStock(stock);
//stock.getStockDailyRecords().add(stockDailyRecords); // COMMENTED OUT THIS LINE
session.save(stock);
session.save(stockDailyRecords);

Then I was able to prevent that update which is really not necessary. And i got the resultsimilar to that of case 5. So, what is the difference then?

Pradip Saha
Guest
Pradip Saha

lot of thanx

Alen Jain
Guest
Alen Jain

As you say someone is relationship owner and it will take responsibility to maintain relationship.. Let me tell you this line becomes a most confusing one. In example you save both the objects STOCK as well as Stock_Daily_Record.
In inverse=true, Stock_Daily_Record is relationship owner OR inverse=false where STOCK is relationship owner. In both of these case why do you save both objects ?
Because if you see code wise both looks similar.

Junaid Anjum
Guest
Junaid Anjum
Hi Mkyong, Thanks for writing such a good article. Your article really makes it easy to understand. But my problem is I am using inverse=”true” i.e. stockDailyRecords is the owner. In first step I inserted stockDailyRecords record so it will generate two queries 1) insert in stockDailyRecords table and 2) insert in stock table In second step I am updating stockDailyRecords so it will generate two queries.. 1) update stockDailyRecords table and 2) insert in stock table but in this case I am getting unique constraint violated because it is trying to insert in the same record in stock twoice.… Read more »
Mohan
Guest
Mohan

Thank you. Much clear now.

Az MaYo
Guest
Az MaYo

Once again clear my confusion.

allabakash
Guest
allabakash

Awesome, lucid and straight-forward explanation. Thanks a lot.

Ameya
Guest
Ameya

You saved my day! Thanks!
However, I have one query. I saw this statement in this post:
“In few articles, they even suggested that just forget about what is “inverse”, and always put inverse=”true” in the collection variable.”
Are we not supposed to use inverse=”false”. Why?
My implementation is like this:
I am maintaining only one-to-many association in XML, not many-to-one. In java, I am not giving reference of parent to the child. And, by keeping inverse=”false”, the foreign key is getting updated through the update query.
Is this practice ok? Or should I switch to more conventional two way relationship style?

Madhu
Guest
Madhu

Very nice explaination…It’s a big confusion portion of NHibernate,you resolved it very nicely…

Thanks a Ton…

Paulo Miguel Almeida
Guest
Paulo Miguel Almeida

MKyoung,

First of all, let me congratulate you for this awesome job, your website has been a life saver lately. Keep going.

It’d be nice if you could make some reference to inverse control using annotations too. It worthwhile to say that mappedBy attribute does the same thing when you are using an biderection relationship between @OneToMany(mappedBy=”attributeyouwanttomap”) and @ManyToOne()

Thanks once more for you great job!

Vamsi
Guest
Vamsi

if inverse=”false”
and
When Stock object is saved,

Why we need stockDailyRecord to be saved?

“session.save(stockDailyRecords);”

Gowtham
Guest
Gowtham

saving the stockDailyRecord is based on Cascade .. not on inverse … inverse just make sure who is the owner of the relationship

Vipul Mathur
Guest
Vipul Mathur

very well written & explained.

xf
Guest
xf

very clear . thanks

Ravi
Guest
Ravi

Thanks Mkyong for the nice artice.
In the section:[ inverse=”false” Example], I am not getting what you meant by the below:
“Note
Again, the third statement is NOT necessary.”

Which third statement are you referring to? Please explain.

Nikunj
Guest
Nikunj

In the Update Example of the (Inverse = false) , Actually there was not any third statement ,it was by mistake written that “Again, the third statement is NOT necessary.” , so Instead of third statement he is referring to the second update statement actually.
Hence it was “Again, the second statement is NOT necessary.”

abhishek h joshi
Guest
abhishek h joshi

Hi MkYong,

Its a really nice article.

Can you please post your code for download purpose.
It will definitely make our understanding lot better.Thanks in advance.

Abhishek J

shilpa
Guest
shilpa

very good artical with practical example.Very clear.Thanks a lot for making me understand.

shareef
Guest
shareef

This is a link very short definition of when to use inverse=true/false

http://tadtech.blogspot.com/2007/02/hibernate-when-is-inversetrue-and-when.html

Martin Gainty
Guest
Martin Gainty

I used to work for RH and I asked the same thing
Why does Gavin use variable-names that have nothing to do with the function the variable performs.
inverse means nothing..he should change it to relationship-owner
I think Gavin coded this before Collection came into play..so from what i see
1)Hibernates extension of Java collection classes makes no sense with new generic impl’s
2)I worked at one installation on the Pacific Coast that ripped Hibernate out of their code because the CTO said it is an ill-named,undocumented,resource-hogging piece of !!!!
Martin-
Confusion and Obfuscation are the main tactics used in battling adversaries..Sun Tsu

Vijay
Guest
Vijay

Gr8 Example!

Hojatv
Guest
Hojatv

As clear as ever. Thanks mkyong.

chhaya
Guest
chhaya

Hi ,

I am still confused with inverse attribute.

In the above ex when cascade is none and inverse is false. then it firing three quires one for parent insert one for child insert and one for constraint update.

My ques is when we are using cascade none then why we need to write below line.
stock.getStockDailyRecords().add(stockDailyRecords);

one extra update query I am seeing because of above line in cascade none. Please clear my confusion.

Biswaa
Guest
Biswaa

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