Question

Unique constraint on two fields of a table with EJB3

Asked by: serrutom

Is it possible to put a unique constraint on an entity based on two or more fields?

I have a company entity which has a code and name field. It should not be possible to add a second database entry with the same code-name combination.
But it should be possible to a two companies with the same name and a different code.

For example:

id: 1
code: xxx
name: company1

id: 2
code: xxx
name: company2

id: 3
code: yyy
name: company1

The entities above are allowed, but the entity below should be rejected when it is added.

id: 4
code: xxx
name: company1


My entity looks like this right now:

@Entity
@Table(name = "COMPANY", uniqueConstraints = { @UniqueConstraint(columnNames = { "code" }), @UniqueConstraint(columnNames = { "name" }) })
public class Company {
     ...
}

                                  
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Asked On
2009-10-28 at 06:48:32ID24850831
Tags

ejb

,

unique

,

constraint

,

database

Topics

Enterprise Java Beans (EJB)

,

Java Programming Language

,

J2EE

Participating Experts
2
Points
500
Comments
5

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Answers

 

by: MRomaniPosted on 2009-10-28 at 06:55:33ID: 25683231

basically you would need to have a function that checks to see if there is a matching (code,company) that already exists, and if so, dont add, else its ok to add.

 

by: ozlevanonPosted on 2009-10-28 at 08:18:08ID: 25684190

Try to use this:
@Table(name = "COMPANY", uniqueConstraints = { @UniqueConstraint(columnNames = { "code" , "name" }) })

See the full class example below
When trying to save an item with a combination of code/name that already exists, it throws
4797 [main] WARN org.hibernate.util.JDBCExceptionReporter - SQL Error: -104, SQLState: 23000
4797 [main] ERROR org.hibernate.util.JDBCExceptionReporter - Unique constraint violation: SYS_CT_7 in statement [insert into COMPANY (USER_ID, code, name) values (null, ?, ?)]
2009-10-28 17:15:51,774 - [ERROR      ] [GENERAL             ] Hibernate DB: Error persisting object (class=class com.mobixell.adselector.hibernate.Company): org.hibernate.exception.ConstraintViolationException: could not insert: [com.mobixell.adselector.hibernate.Company]
2009-10-28 17:15:51,774 - Exception in Hibernate DB at:
2009-10-28 17:15:51,774 - org.hibernate.exception.ConstraintViolationException: could not insert: [com.mobixell.adselector.hibernate.Company]
...

import javax.persistence.*;
 
@Entity
@Table(name = "COMPANY", uniqueConstraints = { @UniqueConstraint(columnNames = { "code" , "name" }) })
public class Company
{
	@Id
	@Column(name = "USER_ID")
	@GeneratedValue(strategy = GenerationType.AUTO)
	private Integer id;
 
	private String code = null;
	private String name = null;
 
	public Company()
	{
	}
 
	public Company(String code, String name)
	{
		this.code = code;
		this.name = name;
	}
 
	public Integer getId()
	{
		return id;
	}
 
	public void setId(Integer id)
	{
		this.id = id;
	}
 
	public String getCode()
	{
		return code;
	}
 
	public void setCode(String code)
	{
		this.code = code;
	}
 
	public String getName()
	{
		return name;
	}
 
	public void setName(String name)
	{
		this.name = name;
	}
 
 
	@Override
	public String toString()
	{
		return "Company{" +
			   "id=" + id +
			   ", code='" + code + '\'' +
			   ", name='" + name + '\'' +
			   '}';
	}
}
                                              
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by: serrutomPosted on 2009-10-28 at 08:31:09ID: 25684367

Is it also possible to check for a certain value?

If i have a 'code' field and an 'isDeleted' field, and i want to check if there is an entity in the database which has the same code, and is active.

- If there is no entity in the database with the same code and where isDeleted = false, then i'm allowed to add.
- If there is an entity in the database with the same code and where isDeleted = false, then i'm not allowed to add.
- If isDeleted = true, then the entity is not taken into account for the check

import javax.persistence.*;
 
@Entity
@Table(name = "COMPANY", uniqueConstraints = { @UniqueConstraint(columnNames = { "code" , "isDeleted" }) })
public class Company
{
        @Id
        @GeneratedValue(strategy = GenerationType.AUTO)
        private Integer id;
        private String code = null;
        private String name = null;
        private Boolean isDeleted = false;
 
...
}

                                              
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by: ozlevanonPosted on 2009-10-28 at 09:05:32ID: 25684760

As far as I know (and from a small test I just ran) the unique constraint doesn't apply to NULL values. e.g. you could have the same code and name combo if the name is null in both.
You can do what you ask by changing the isDeleted field to isActive and using NULL when it's deleted, and a specific concrete value (e.g. true), which it's active.
This will allow you to have as many combinations as you want  of the same code where isActive =NULL, but only one instance of a specific code with isActive=true

I hope this was clear (and that it works).

 

by: serrutomPosted on 2009-10-28 at 09:36:43ID: 31646958

Thanks a lot!

20120131-EE-VQP-002

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