Solved

unique=true in hibernate

Posted on 2011-03-24
9
499 Views
Last Modified: 2012-05-11
I would like to know more about unique=true in hibernate. Where and how and why to use it. How to use it for many-many, one-many, many-one, one-one Any ideas, resources, links, sample code highly appreciated. thanks in advance.


Getting more confused especially with one-one where for example many students can have same address in this scenario STUDENT_ADDRESS column under student table is set to unique in STUDENT.hbm.xml file.
http://www.vaannila.com/hibernate/hibernate-example/hibernate-mapping-one-to-one-1.html

similarly in one-many example where one student can have many phone numbers the phone id kept as unique within set collection of many-many tag.
http://www.vaannila.com/hibernate/hibernate-example/hibernate-mapping-one-to-many-1.html
please advise.
0
Comment
Question by:gudii9
  • 6
  • 2
9 Comments
 
LVL 47

Accepted Solution

by:
for_yan earned 167 total points
Comment Utility
Frankly, the example about students and phones does not seem very starightforward to me either (maybe someone else will eplain it to us),
however the concept of unique=true is really simple.
In this way you communicate to hibernate that according to your design this field cannot have the same
value in two different rows - this would allow to apply unique constraint to the corrresponding column
which stores this field in the table. This in many cases can make many database operations
more effective and would allow databse to do the check on insert
which would catcth possible mistkes long before they can create real problems for your data.
0
 
LVL 20

Expert Comment

by:Sathish David Kumar N
Comment Utility
unique is the one of  the property element  used by Hibernate's DDL generation .
To create the unique index in database.. You will not do anything with that hibernate will take care while ur using unique =true ! then Hiberante will increase the index value .
0
 
LVL 20

Expert Comment

by:Sathish David Kumar N
Comment Utility
Sorry i am getting your other question please tell bit clear !!
0
 
LVL 20

Expert Comment

by:Sathish David Kumar N
Comment Utility
sorry i am leaking little bit in english...
0
How your wiki can always stay up-to-date

Quip doubles as a “living” wiki and a project management tool that evolves with your organization. As you finish projects in Quip, the work remains, easily accessible to all team members, new and old.
- Increase transparency
- Onboard new hires faster
- Access from mobile/offline

 
LVL 7

Author Comment

by:gudii9
Comment Utility
I was confused on how to define unique inside mapping file for many-many, many-one, one-one etc. please advise
0
 
LVL 20

Assisted Solution

by:Sathish David Kumar N
Sathish David  Kumar N earned 333 total points
Comment Utility
This parameter are you can use in u can define like that !! what ever you need !
<many-to-one
  name="propertyName"
column="column_name"
class="ClassName"
cascade="cascade_style"
fetch="join|select"
update="true|false"
insert="true|false"
property-ref="propertyNameFromAssociatedClass"
access="field|property|ClassName"
unique="true|false"
not-null="true|false"
optimistic-lock="true|false"
lazy="true|false"
entity-name="EntityName"
/>

0
 
LVL 20

Expert Comment

by:Sathish David Kumar N
Comment Utility
(1)name: The name of the property.  
(2) column (optional): The name of the foreign key column. This may also be specified by nested <column> element(s).  
(3) class (optional - defaults to the property type determined by reflection): The name of the associated class.  
(4) cascade (optional): Specifies which operations should be cascaded from the parent object to the associated object.  
(5) join (optional - defaults to select): Chooses between outer-join fetching or sequential select fetching.  
(6) update, insert (optional - defaults to true) specifies that the mapped columns should be included in SQL UPDATE and/or INSERT statements. Setting both to false allows a pure "derived" association whose value is initialized from some other property that maps to the same colum(s) or by a trigger or other application.  
(7) property-ref: (optional) The name of a property of the associated class that is joined to this foreign key. If not specified, the primary key of the associated class is used.  
(8) access (optional - defaults to property): The strategy Hibernate should use for accessing the property value.  
(9) unique (optional): Enable the DDL generation of a unique constraint for the foreign-key column. Also, allow this to be the target of a property-ref. This makes the association multiplicity effectively one to one.  
(10) not-null (optional): Enable the DDL generation of a nullability constraint for the foreign key columns.  
(11) optimistic-lock (optional - defaults to true): Specifies that updates to this property do or do not require acquisition of the optimistic lock. In other words, dertermines if a version increment should occur when this property is dirty.  
(12) lazy (optional - defaults to false): Specifies that this property should be fetched  
0
 
LVL 20

Assisted Solution

by:Sathish David Kumar N
Sathish David  Kumar N earned 333 total points
Comment Utility
Thats key element is common for many-to-many,one-to -one,many-to-one
0
 
LVL 7

Author Comment

by:gudii9
Comment Utility
>>>unique (optional): Enable the DDL generation of a unique constraint for the foreign-key column. Also, allow this to be the target of a property-ref. This makes the association multiplicity effectively one to one.  


please elaborate on this. I was not clear.
0

Featured Post

6 Surprising Benefits of Threat Intelligence

All sorts of threat intelligence is available on the web. Intelligence you can learn from, and use to anticipate and prepare for future attacks.

Join & Write a Comment

Suggested Solutions

After being asked a question last year, I went into one of my moods where I did some research and code just for the fun and learning of it all.  Subsequently, from this journey, I put together this article on "Range Searching Using Visual Basic.NET …
Basic understanding on "OO- Object Orientation" is needed for designing a logical solution to solve a problem. Basic OOAD is a prerequisite for a coder to ensure that they follow the basic design of OO. This would help developers to understand the b…
Viewers will learn one way to get user input in Java. Introduce the Scanner object: Declare the variable that stores the user input: An example prompting the user for input: Methods you need to invoke in order to properly get  user input:
This tutorial covers a step-by-step guide to install VisualVM launcher in eclipse.

728 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

9 Experts available now in Live!

Get 1:1 Help Now