@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"})
public String username;

But I'm getting some error:

@UniqueConstraint is dissallowed for this location

What's the proper way to use unique constraints?

Note: I am using play framework.

Solution 1

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

Solution 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;
}

Solution 3

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.

Solution 4

Note: In Kotlin the syntax for declaring the arrays in annotations uses arrayOf(...) instead of {...}

@Entity
@Table(uniqueConstraints=arrayOf(UniqueConstraint(columnNames=arrayOf("book", "chapter_number"))))
class Chapter(@ManyToOne var book:Book,
              @Column var chapterNumber:Int)

Note: As of Kotlin 1.2 its is possible to use the [...] syntax so the code become much simpler

@Entity
@Table(uniqueConstraints=[UniqueConstraint(columnNames=["book", "chapter_number"])])
class Chapter(@ManyToOne var book:Book,
              @Column var chapterNumber:Int)

Solution 5

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

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Comments

[Jon Skeet]

"But am geting some error." Always specify what error you're getting in the question. You have relevant information which may very well help us to solve your problem - don't keep it to yourself.

[naoru]

Its important to note that it will only work if you let JPA create your tables

[Stimpson Cat]

I hope you do not code with these fields in real life ;)

[FrancescoM]

Of course not, but i do write examples with such fields :D