如何使用 JPA 创建 UNIQUE 列？

Question

My POJO is using JPA and when I apply unique value in the column is not working for me I tried to use the UniqueConstraint and also not working for me.

below is my code

@Entity
@Table(name = "users", uniqueConstraints={@UniqueConstraint(columnNames = {"user_id"}),@UniqueConstraint(columnNames = {"username"}),@UniqueConstraint(columnNames = {"email"})})

    public class Users {

     @Id
     @GeneratedValue(strategy = GenerationType.AUTO)
     @Column(name="user_id",unique=true,nullable = false)
     private int UserId;

     @Column(name = "username" ,unique=true,nullable = false)
     private String Username;

     @Column(name = "email",unique=true ,nullable = false)
     private String email;

     @Column(name = "firstname",nullable = false)
     private String firstname;

     @Column(name = "lastname", nullable = false)
     private String lastname;

     @Column(name = "password", nullable = false)
     private String password;

     @Column(name = "active")
     private int active;

     @ManyToMany(cascade=CascadeType.ALL)
     @JoinTable(name="user_role", joinColumns=@JoinColumn(name="user_id"), inverseJoinColumns=@JoinColumn(name="role_id"))
     private Set<Role> roles;

below is the generated table in the database (MySQL)

| users | CREATE TABLE users (
  user_id int(11) NOT NULL,
  username varchar(255) NOT NULL,
  active int(11) DEFAULT NULL,
  email varchar(255) NOT NULL,
  firstname varchar(255) NOT NULL,
  lastname varchar(255) NOT NULL,
  password varchar(255) NOT NULL,
  PRIMARY KEY (user_id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 |

Hibernate log after spring start

Hibernate: create table users (user_id integer not null, username varchar(255) not null, active integer, email varchar(255) not null, firstname varchar(255) not null, lastname varchar(255) not null, password varchar(255) not null, primary key (user_id)) engine=InnoDB Hibernate: alter table users drop index UKfnranlqhubvw04boopn028e6 Hibernate: alter table users add constraint UKfnranlqhubvw04boopn028e6 unique (username, email) Hibernate: alter table users drop index UK_r43af9ap4edm43mmtq01oddj6 Hibernate: alter table users add constraint UK_r43af9ap4edm43mmtq01oddj6 unique (username) Hibernate: alter table users drop index UK_6dotkott2kjsp8vw4d0m25fb7

Answer 1

Try like this:

 @Entity
    @Table(name="users",uniqueConstraints=@UniqueConstraint(columnNames={"user_id","username","email"}))

        public class Users {

Answer 2

Apparently there's nothing wrong with this code. unique=true in @Column is a shortcut for @UniqueConstraint(columnNames = {"user_id"} and other particular constraints. You could only use one of them except for multiple unique constraints.

But if you are confused why the generated CREATE TABLE doesn't contain these unique constraints, check the log, you can find alter table commands just after CREATE TABLE .

In this case commands could be,

alter table users add constraint UK_some_id unique (username)
alter table users add constraint UK_some_id unique (email)

Hope this help.

Answer 3

in jpa the id is already unique so to make username and email unique add the statement

unique=true

to the corresponding @Column annotation.

PS : remember the unique cannot be null when insert new item you should drop the table before run the application and remove uniqueConstraints in table annotation

Answer 4

if you set unique in @Column that's mean let your JPA provider create the database for you - it will create the unique constraint on the specified column.

But after creating a database, or you alter it once created, then unique doesn't have any effect

Answer 5

I had the same problem here, set length to your unique columns.. It worked here. Do

@Column(name = "userName", length = 50, unique = true)

Answer 6

Set the column to have the fixed length make it work because mysql size for unique constrains limited to 1000 bytes

@Column(name = "username", length = 200, unique = true)

Answer 7

Use @javax.persistence.Column(unique = true). Dont forget to restart your application.

&& you cant alter your column if there are still duplicated values in it. drop your table, and recreate it with your generated ddl. (if ure not usin springboot)

&& if youre using springboot, go to your application.properties & set spring.jpa.hibernate.ddl-auto to update

This updates the schema if necessary.

Answer 8

The column needs to be non nullable for it to be unique!

@Column(unique = true) will NOT work

@Column(unique = true, nullable = false) will work

Answer 9

If the database or schema already exists before adding the uniqueConstraints then it won't work.

So drop the database or schema and run the application to create new database with these uniqueConstraints

DROP DATABASE database_name;