@UniqueConstraint annotation in Java

Question

I have a Java bean. Now, I want to be sure that the field should be unique.

I am using the following code:

@UniqueConstraint(columnNames={\"username\         


        

Answer 1

I'm currently using play framework too with hibernate and JPA 2.0 annotation and this model works without problems

@Entity
@Table(uniqueConstraints={@UniqueConstraint(columnNames = {"id_1" , "id_2"})})
public class class_name {

@Id
@GeneratedValue
public Long id;

@NotNull
public Long id_1;

@NotNull
public Long id_2;

}

Hope it helped.

Answer 2

You can use at class level with following syntax

@Entity
@Table(uniqueConstraints={@UniqueConstraint(columnNames={"username"})})
public class SomeEntity {
    @Column(name = "username")
    public String username;
}

Answer 3

you can use @UniqueConstraint on class level, for combined primary key in a table. for example:

 @Entity
 @Table(name = "PRODUCT_ATTRIBUTE", uniqueConstraints = {
       @UniqueConstraint(columnNames = {"PRODUCT_ID"}) })

public class ProductAttribute{}

Answer 4

Way1 :

@Entity

@Table(name = "table_name", uniqueConstraints={@UniqueConstraint(columnNames = "column1"),@UniqueConstraint(columnNames = "column2")})

-- Here both Column1 and Column2 acts as unique constraints separately. Ex : if any time either the value of column1 or column2 value matches then you will get UNIQUE_CONSTRAINT Error.

Way2 :

@Entity

@Table(name = "table_name", uniqueConstraints={@UniqueConstraint(columnNames ={"column1","column2"})})

-- Here both column1 and column2 combined values acts as unique constraints

Answer 5

   @Entity @Table(name = "stock", catalog = "mkyongdb",
   uniqueConstraints = @UniqueConstraint(columnNames =
   "STOCK_NAME"),@UniqueConstraint(columnNames = "STOCK_CODE") }) public
   class Stock implements java.io.Serializable {

   }

Unique constraints used only for creating composite key ,which will be unique.It will represent the table as primary key combined as unique.

Answer 6

To ensure a field value is unique you can write

@Column(unique=true)
String username;

The @UniqueConstraint annotation is for annotating multiple unique keys at the table level, which is why you get an error when applying it to a field.

References (JPA TopLink):

• @UniqueConstraint
• @Column