@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.

"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. — Jon Skeet, Jun 27 '10 at 08:09

score 500 · Answer 1 · edited Apr 14 '15 at 22:53

500

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):

edited Apr 14 '15 at 22:53

pimlottc

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answered Jun 27 '10 at 08:16

mdma

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Its important to note that it will only work if you let JPA create your tables – naoru May 10 '18 at 21:04

score 139 · Answer 2 · answered Jul 24 '13 at 05:12

139

You can use at class level with following syntax

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

answered Jul 24 '13 at 05:12

Divanshu

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score 49 · Answer 3 · edited Feb 27 '15 at 04:23

49

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.

edited Feb 27 '15 at 04:23

Stephan

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answered Jul 28 '14 at 10:00

FrancescoM

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4

I hope you do not code with these fields in real life ;) – Stimpson Cat Feb 04 '21 at 08:22
1

Of course not, but i do write examples with such fields :D – FrancescoM Dec 16 '21 at 12:01

score 32 · Answer 4 · edited Dec 04 '17 at 23:55

32

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)

edited Dec 04 '17 at 23:55

Larrikin

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answered Jun 17 '16 at 17:49

GlenPeterson

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Thanks @Larrikin - that really improves the answer! – GlenPeterson Jan 28 '21 at 00:47

Manjunath H M · Answer 5 · 2021-09-23T16:32:30.143

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

score 7 · Answer 6 · answered Feb 14 '21 at 03:54

@UniqueConstraint this annotation is used for annotating single or multiple unique keys at the table level separated by comma, which is why you get an error. it will only work if you let JPA create your tables

Example

@NoArgsConstructor
@AllArgsConstructor
@Getter
@Setter
@Builder(builderClassName = "Builder", toBuilder = true)
@Entity
@Table(name = "users", uniqueConstraints = @UniqueConstraint(columnNames = {"person_id", "company_id"}))
public class AppUser extends BaseEntity {

    @Column(name = "person_id")
    private Long personId;

    @ManyToOne
    @JoinColumn(name = "company_id")
    private Company company;
}

https://docs.jboss.org/hibernate/jpa/2.1/api/javax/persistence/UniqueConstraint.html

On the other hand To ensure a field value is unique you can write

@Column(unique=true)
String username;

score 7 · Answer 7 · answered Jun 26 '21 at 08:31

Defining the Column Constraints

Whenever the unique constraint is based only on one field, we can use @Column(unique=true) on that column.

Let's define a unique constraint on the personNumber field:

@Column(unique=true)
private Long personNumber;

When we execute the schema creation process, we can validate it from the logs:

[main] DEBUG org.hibernate.SQL -
    alter table Person add constraint UK_d44q5lfa9xx370jv2k7tsgsqt unique (personNumber)

Defining Unique Constraints

JPA helps us to achieve that with the @UniqueConstraint annotation. We do that in the @Table annotation under the uniqueConstraints attribute. Let's remember to specify the names of the columns:

@Table(uniqueConstraints = { @UniqueConstraint(columnNames = { "personNumber", "isActive" }) })

We can validate it once the schema is generated:

[main] DEBUG org.hibernate.SQL -
    alter table Person add constraint UK5e0bv5arhh7jjhsls27bmqp4a unique (personNumber, isActive)

score 5 · Answer 8 · edited Oct 15 '14 at 05:52

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.

edited Oct 15 '14 at 05:52

Pradhan

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answered Oct 15 '14 at 05:07

CodamRanjan

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score 4 · Answer 9 · edited Jun 24 '22 at 08:42

4

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{}

edited Jun 24 '22 at 08:42

Apostolos

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answered Nov 29 '16 at 07:10

hashem yousefi

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score 2 · Answer 10 · edited Apr 12 '19 at 13:24

Unique annotation should be placed right above the attribute declaration. UniqueContraints go into the @Table annotation above the data class declaration. See below:

@Entity
@Table(uniqueConstraints= arrayOf(UniqueConstraint(columnNames = arrayOf("col_1", "col_2"))))
data class Action(
        @Id @GeneratedValue @Column(unique = true)
        val id: Long?,
        val col_1: Long?,
        val col_2: Long?,
)

score 1 · Answer 11 · answered Feb 14 '21 at 01:27

The value of the length property must be greater than or equal to name atribute length, else throwing an error.

Works

@Column(name = "typ e", length = 4, unique = true)
private String type;

Not works, type.length: 4 != length property: 3

@Column(name = "type", length = 3, unique = true)
private String type;

score 1 · Answer 12 · answered Jul 19 '21 at 11:02

1

For me adding @Column(name = "column_name", length = 11, unique = true) worked

answered Jul 19 '21 at 11:02

PKS

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score 0 · Answer 13 · answered Nov 30 '22 at 22:02

Be aware when using @UniqueConstraint :

In Some cases( when using MySql), we have to provide the length of columns used in unique contraint by adding @Column(name="product_id", length = 6), because by default Hibernate will create columns with the max size (default behavior) which generate an error in MySql when creating the unique constraint (Specified key was too long; max key length is 1000 bytes)