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

User · Answer

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;

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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    quot Builder quot   toBuilder   true   Entity  Table name    quot users quot   uniqueConstraints    UniqueConstraint columnNames     quot person id quot    quot company id quot     public class AppUser extends BaseEntity         Column name    quot person id quot       private Long personId        ManyToOne      JoinColumn name    quot company id quot       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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

You can use at class level with following syntax   Entity  Table uniqueConstraints   UniqueConstraint columnNames   username      public class SomeEntity        Column name    username       public String username

[java] @UniqueConstraint annotation in Java

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