The attribute 'uniqueConstraints' of @Table annotation can be used to apply unique constraints to the specified fields.
@Table annotation:
package javax.persistence;
....
public @interface Table {
....
/**
* (Optional) Unique constraints that are to be placed on
* the table. These are only used if table generation is in
* effect. These constraints apply in addition to any constraints
* specified by the <code>Column</code> and <code>JoinColumn</code>
* annotations and constraints entailed by primary key mappings.
* <p> Defaults to no additional constraints.
*/
UniqueConstraint[] uniqueConstraints() default {};
....
}
@UniqueConstraint annotation:
package javax.persistence;
....
public @interface UniqueConstraint {
/** (Optional) Constraint name. A provider-chosen name will be chosen
* if a name is not specified.
*
* @since Java Persistence 2.0
*/
String name() default "";
/** (Required) An array of the column names that make up the constraint. */
String[] columnNames();
}
Example
Entity
@Entity
@Table(uniqueConstraints = {
@UniqueConstraint(columnNames = "name", name = "uniqueNameConstraint")}
)
public class Employee {
@Id
@GeneratedValue
private long id;
private String name;
private String dept;
.............
}
Main class
Checking generated constraints and persisting/loading data:
public class ExampleMain {
private static EntityManagerFactory entityManagerFactory =
Persistence.createEntityManagerFactory("example-unit");
public static void main(String[] args) {
try {
//constraint assigned to Employee table:
runNativeQuery("SELECT * FROM INFORMATION_SCHEMA.CONSTRAINTS WHERE TABLE_NAME='EMPLOYEE'");
//column names of CONSTRAINTS table:
runNativeQuery("SELECT COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME='CONSTRAINTS'");
persistEmployees();
findAllEmployees();
} finally {
entityManagerFactory.close();
}
}
private static void findAllEmployees() {
System.out.println("-- Employees with phone number NOT 222-222-222 --");
EntityManager entityManager = entityManagerFactory.createEntityManager();
TypedQuery<Employee> query = entityManager
.createQuery("Select e from Employee e", Employee.class);
List<Employee> list = query.getResultList();
list.forEach(System.out::println);
entityManager.close();
}
private static void runNativeQuery(String s) {
System.out.printf("-- %s --%n", s);
EntityManager entityManager = entityManagerFactory.createEntityManager();
Query query = entityManager.createNativeQuery(s);
List list = query.getResultList();
for (Object o : list) {
if (o instanceof Object[]) {
System.out.println(Arrays.toString((Object[]) o));
} else {
System.out.println(o);
}
}
}
public static void persistEmployees() {
Employee employee1 = Employee.of("Diana", "IT");
Employee employee2 = Employee.of("Mike", "Admin");
Employee employee3 = Employee.of("Tim", "Sales");
EntityManager em = entityManagerFactory.createEntityManager();
em.getTransaction().begin();
em.persist(employee1);
em.persist(employee2);
em.persist(employee3);
em.getTransaction().commit();
em.close();
}
}-- SELECT * FROM INFORMATION_SCHEMA.CONSTRAINTS WHERE TABLE_NAME='EMPLOYEE' --
[TEST, PUBLIC, UNIQUENAMECONSTRAINT, UNIQUE, TEST, PUBLIC, EMPLOYEE, UNIQUENAMECONSTRAINT_INDEX_7, null, NAME, , ALTER TABLE PUBLIC.EMPLOYEE ADD CONSTRAINT PUBLIC.UNIQUENAMECONSTRAINT UNIQUE(NAME) INDEX PUBLIC.UNIQUENAMECONSTRAINT_INDEX_7, 9]
[TEST, PUBLIC, CONSTRAINT_7, PRIMARY_KEY, TEST, PUBLIC, EMPLOYEE, PRIMARY_KEY_7, null, ID, , ALTER TABLE PUBLIC.EMPLOYEE ADD CONSTRAINT PUBLIC.CONSTRAINT_7 PRIMARY KEY(ID) INDEX PUBLIC.PRIMARY_KEY_7, 7]
-- SELECT COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME='CONSTRAINTS' --
CONSTRAINT_CATALOG
CONSTRAINT_SCHEMA
CONSTRAINT_NAME
CONSTRAINT_TYPE
TABLE_CATALOG
TABLE_SCHEMA
TABLE_NAME
UNIQUE_INDEX_NAME
CHECK_EXPRESSION
COLUMN_LIST
REMARKS
SQL
ID
-- Employees with phone number NOT 222-222-222 --
Employee{id=1, name='Diana', dept='IT'}
Employee{id=2, name='Mike', dept='Admin'}
Employee{id=3, name='Tim', dept='Sales'}
Also see Queries involving INFORMATION_SCHEMA.
Violating unique constraint
If we try to save the same name for multiple Employees then ConstraintViolationException will be thrown:
public class ExampleMain2 {
private static EntityManagerFactory entityManagerFactory =
Persistence.createEntityManagerFactory("example-unit");
public static void main(String[] args) {
try {
persistEmployees();
} finally {
entityManagerFactory.close();
}
}
public static void persistEmployees() {
Employee employee1 = Employee.of("Diana", "IT");
Employee employee2 = Employee.of("Diana", "Admin");
EntityManager em = entityManagerFactory.createEntityManager();
em.getTransaction().begin();
em.persist(employee1);
em.persist(employee2);
em.getTransaction().commit();
em.close();
}
}
......
Caused by: org.hibernate.exception.ConstraintViolationException: could not execute statement
at org.hibernate.exception.internal.SQLStateConversionDelegate.convert(SQLStateConversionDelegate.java:112)
at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:42)
at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:113)
at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:99)
at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:178)
at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:3171)
at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:3686)
at org.hibernate.action.internal.EntityInsertAction.execute(EntityInsertAction.java:90)
at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:604)
at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:478)
at org.hibernate.event.internal.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:356)
at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:39)
at org.hibernate.internal.SessionImpl.doFlush(SessionImpl.java:1454)
at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:511)
at org.hibernate.internal.SessionImpl.flushBeforeTransactionCompletion(SessionImpl.java:3283)
at org.hibernate.internal.SessionImpl.beforeTransactionCompletion(SessionImpl.java:2479)
at org.hibernate.engine.jdbc.internal.JdbcCoordinatorImpl.beforeTransactionCompletion(JdbcCoordinatorImpl.java:473)
at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl.beforeCompletionCallback(JdbcResourceLocalTransactionCoordinatorImpl.java:178)
at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl.access$300(JdbcResourceLocalTransactionCoordinatorImpl.java:39)
at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl$TransactionDriverControlImpl.commit(JdbcResourceLocalTransactionCoordinatorImpl.java:271)
at org.hibernate.engine.transaction.internal.TransactionImpl.commit(TransactionImpl.java:98)
... 2 more
Caused by: org.h2.jdbc.JdbcSQLException: Unique index or primary key violation: "UNIQUENAMECONSTRAINT_INDEX_7 ON PUBLIC.EMPLOYEE(NAME) VALUES ('Diana', 1)"; SQL statement:
insert into Employee (dept, name, id) values (?, ?, ?) [23505-197]
at org.h2.message.DbException.getJdbcSQLException(DbException.java:357)
at org.h2.message.DbException.get(DbException.java:179)
at org.h2.message.DbException.get(DbException.java:155)
at org.h2.index.BaseIndex.getDuplicateKeyException(BaseIndex.java:101)
at org.h2.mvstore.db.MVSecondaryIndex.requireUnique(MVSecondaryIndex.java:236)
at org.h2.mvstore.db.MVSecondaryIndex.add(MVSecondaryIndex.java:202)
at org.h2.mvstore.db.MVTable.addRow(MVTable.java:732)
at org.h2.command.dml.Insert.insertRows(Insert.java:182)
at org.h2.command.dml.Insert.update(Insert.java:134)
at org.h2.command.CommandContainer.update(CommandContainer.java:102)
at org.h2.command.Command.executeUpdate(Command.java:261)
at org.h2.jdbc.JdbcPreparedStatement.executeUpdateInternal(JdbcPreparedStatement.java:199)
at org.h2.jdbc.JdbcPreparedStatement.executeUpdate(JdbcPreparedStatement.java:153)
at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:175)
... 18 more
Example ProjectDependencies and Technologies Used: - h2 1.4.197: H2 Database Engine.
- hibernate-core 5.3.6.Final: Hibernate's core ORM functionality.
Implements javax.persistence:javax.persistence-api version 2.2 - hibernate-jpamodelgen 5.3.6.Final: Annotation Processor to generate JPA 2 static metamodel classes.
- JDK 1.8
- Maven 3.5.4
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