@Column annotation specify the details about this column.
Below table summarizes the attributes of @Column annotation.
|
Attribute |
Description |
Data type |
|
name |
Specify the column name. Field or property name is taken by default. |
String |
|
unique |
Specify whether this column has unique key constraint or not. |
boolean |
|
nullable |
Specifies whether the column take null value or not. |
boolean |
|
insertable |
Specifies whether the column is included in SQL INSERT statements generated by the persistence provider. |
boolean |
|
updatable |
Specifies Whether the column is included in SQL UPDATE statements generated by the persistence provider. |
boolean |
|
columnDefinition |
Specifies the SQL fragment that is used when generating the DDL for the column. |
String |
|
table |
Specifies the name of the table that contains the column. If absent the column is assumed to be in the primary table. |
String |
|
length |
Specifies he column length. It applies only if a string-valued column is used. |
int |
|
precision |
Specifies the precision for a decimal (exact numeric) column. (Applies only if a decimal column is used.) Value must be set by developer if used when generating the DDL for the column. |
int |
|
scale |
Specifies the scale for a decimal (exact numeric) column. Applies only if a decimal column is used.) |
int |
Example 1: Specifies the column 'person_name' with lenght 512 characters and apply not null constraint.
@Column(name = "person_name", nullable = false, length = 512)
private String name;
Example 2: Explcitly set the type to TEXT and apply not null constraint.
@Column(columnDefinition = "TEXT NOT NULL")
private String description;
Example 3: Make sure that this column is not updatable and
not null also.
@Column(name = "created_ts", nullable = false, updatable = false)
private Timestamp createdTimestamp;
Example 4: Example on precision and scale
Column(name="order_cost", updatable=false, precision=12, scale=2)
public BigDecimal getCost() { return cost; }
Precision refers to the maximum number of digits that are present in the number. For example, 12345.67 has a precision of 7. Scale refers to the maximum number of decimal places in the number. For example, 12345.67 has a scale of 2.
Thus the maximum allowed value for decimal(7,2) is 99999.99
Find the below Person entity class.
@Entity
@Table(name = "person")
public class Person {
@Id
@GeneratedValue
private Integer id;
@Column(name = "person_name", nullable = false, length = 512)
private String name;
private Integer age;
@Column(columnDefinition = "TEXT NOT NULL")
private String description;
@CreationTimestamp
@Column(name = "created_ts", nullable = false, updatable = false)
private Timestamp createdTimestamp;
..........
..........
}
Above entity generates following DDL.
create table person (
id integer not null,
age integer,
created_ts timestamp(6) not null,
description TEXT NOT NULL,
person_name varchar(512) not null,
primary key (id)
)
Find the below working application.
Step 1: Create new maven project ‘hibernate-column-annotation-demo’.
Step 2: Update pom.xml with maven dependencies.
pom.xml
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.sample.app</groupId>
<artifactId>hibernate-column-annotation-demo</artifactId>
<version>1</version>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<java.version>15</java.version>
<maven.compiler.source>${java.version}</maven.compiler.source>
<maven.compiler.target>${java.version}</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>org.postgresql</groupId>
<artifactId>postgresql</artifactId>
<version>42.4.1</version>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>6.1.2.Final</version>
</dependency>
<dependency>
<groupId>javax.persistence</groupId>
<artifactId>javax.persistence-api</artifactId>
<version>2.2</version>
</dependency>
</dependencies>
</project>
Step 3: Define entity class.
Person.java
package com.sample.app.entity;
import java.sql.Timestamp;
import org.hibernate.annotations.CreationTimestamp;
import jakarta.persistence.Column;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.Id;
import jakarta.persistence.Table;
@Entity
@Table(name = "person")
public class Person {
@Id
@GeneratedValue
private Integer id;
@Column(name = "person_name", nullable = false, length = 512)
private String name;
private Integer age;
@Column(columnDefinition = "TEXT NOT NULL")
private String description;
@CreationTimestamp
@Column(name = "created_ts", nullable = false, updatable = false)
private Timestamp createdTimestamp;
public Person(String name, Integer age, String description) {
this.name = name;
this.age = age;
this.description = description;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public Timestamp getCreatedTimestamp() {
return createdTimestamp;
}
public void setCreatedTimestamp(Timestamp createdTimestamp) {
this.createdTimestamp = createdTimestamp;
}
}
Step 4: Create hibernate.cfg.xml file under src/main/resources folder.
hibernate.cfg.xml
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<!-- Database Connection settings -->
<property name="connection.driver_class">org.postgresql.Driver</property>
<property name="connection.url">jdbc:postgresql://127.0.0.1:5432/test</property>
<property name="connection.username">postgres</property>
<property name="connection.password">postgres</property>
<!-- Enable the logging of all the generated SQL statements to the console -->
<property name="show_sql">true</property>
<!-- Format the generated SQL statement to make it more readable, -->
<property name="format_sql">true</property>
<!-- Hibernate will put comments inside all generated SQL statements to
hint what’s the generated SQL trying to do -->
<property name="use_sql_comments">false</property>
<property name="dialect">org.hibernate.dialect.PostgreSQLDialect</property>
<!-- Drop and re-create the database schema on startup -->
<property name="hbm2ddl.auto">create</property>
<!-- mappings for annotated classes -->
<mapping class="com.sample.app.entity.Person" />
</session-factory>
</hibernate-configuration>
Step 5: Define main application class.
App.java
package com.sample.app;
import java.io.IOException;
import java.net.URISyntaxException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import com.sample.app.entity.Person;
public class App {
private static final SessionFactory SESSION_FACTORY = buildSessionFactory();
private static SessionFactory buildSessionFactory() {
try {
final StandardServiceRegistry standardRegistry = new StandardServiceRegistryBuilder()
.configure("hibernate.cfg.xml").build();
final Metadata metaData = new MetadataSources(standardRegistry).getMetadataBuilder().build();
return metaData.getSessionFactoryBuilder().build();
} catch (Throwable ex) {
throw new ExceptionInInitializerError(ex);
}
}
public static void main(final String args[]) throws ClassNotFoundException, IOException, URISyntaxException {
Person person1 = new Person("Krishna", 23, "I am a traveller");
Person person2 = new Person("Ram", 31, "blogger, Entrepreneur, content writer");
try (final Session session = SESSION_FACTORY.openSession()) {
session.beginTransaction();
session.persist(person1);
session.persist(person2);
session.getTransaction().commit();
}
}
}
Total project structure looks like below.
Run App.java, you will see below messages in console.
Aug 09, 2022 3:29:30 PM org.hibernate.Version logVersion
INFO: HHH000412: Hibernate ORM core version 6.1.2.Final
Aug 09, 2022 3:29:30 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
WARN: HHH10001002: Using built-in connection pool (not intended for production use)
Aug 09, 2022 3:29:30 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001005: Loaded JDBC driver class: org.postgresql.Driver
Aug 09, 2022 3:29:30 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001012: Connecting with JDBC URL [jdbc:postgresql://127.0.0.1:5432/test]
Aug 09, 2022 3:29:30 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001001: Connection properties: {password=****, user=postgres}
Aug 09, 2022 3:29:30 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001003: Autocommit mode: false
Aug 09, 2022 3:29:30 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections <init>
INFO: HHH10001115: Connection pool size: 20 (min=1)
Aug 09, 2022 3:29:31 PM org.hibernate.engine.jdbc.dialect.internal.DialectFactoryImpl logSelectedDialect
INFO: HHH000400: Using dialect: org.hibernate.dialect.PostgreSQLDialect
Aug 09, 2022 3:29:31 PM org.hibernate.metamodel.internal.EntityInstantiatorPojoStandard resolveConstructor
INFO: HHH000182: No default (no-argument) constructor for class: com.sample.app.entity.Person (class must be instantiated by Interceptor)
Hibernate:
drop table if exists person cascade
Aug 09, 2022 3:29:31 PM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@288f173f] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
Aug 09, 2022 3:29:31 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: SQL Warning Code: 0, SQLState: 00000
Aug 09, 2022 3:29:31 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: table "person" does not exist, skipping
Hibernate:
drop sequence if exists person_SEQ
Aug 09, 2022 3:29:31 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: SQL Warning Code: 0, SQLState: 00000
Aug 09, 2022 3:29:31 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: sequence "person_seq" does not exist, skipping
Hibernate: create sequence person_SEQ start with 1 increment by 50
Aug 09, 2022 3:29:31 PM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@2ef0dd86] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
Hibernate:
create table person (
id integer not null,
age integer,
created_ts timestamp(6) not null,
description TEXT NOT NULL,
person_name varchar(512) not null,
primary key (id)
)
Aug 09, 2022 3:29:31 PM org.hibernate.engine.transaction.jta.platform.internal.JtaPlatformInitiator initiateService
INFO: HHH000490: Using JtaPlatform implementation: [org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform]
Hibernate:
select
nextval('person_SEQ')
Hibernate:
select
nextval('person_SEQ')
Hibernate:
insert
into
person
(age, created_ts, description, person_name, id)
values
(?, ?, ?, ?, ?)
Hibernate:
insert
into
person
(age, created_ts, description, person_name, id)
values
(?, ?, ?, ?, ?)
Query the database in PostgreSQL, you will observe that two table person, person_seq are created. ‘person_seq’ table is used to generate sequence numbers that are used in person primary key auto generation.
test=# \d
List of relations
Schema | Name | Type | Owner
--------+------------+----------+----------
public | person | table | postgres
public | person_seq | sequence | postgres
(2 rows)
test=#
test=# SELECT * FROM person;
id | age | created_ts | description | person_name
----+-----+-------------------------+---------------------------------------+-------------
1 | 23 | 2022-08-09 15:29:31.54 | I am a traveller | Krishna
2 | 31 | 2022-08-09 15:29:31.548 | blogger, Entrepreneur, content writer | Ram
(2 rows)
test=#
test=# SELECT * FROM person_seq;
last_value | log_cnt | is_called
------------+---------+-----------
51 | 31 | t
(1 row)
test=#
test=# \d+ person;
Table "public.person"
Column | Type | Collation | Nullable | Default | Storage | Compression | Stats target | Description
-------------+--------------------------------+-----------+----------+---------+----------+-------------+--------------+-------------
id | integer | | not null | | plain | | |
age | integer | | | | plain | | |
created_ts | timestamp(6) without time zone | | not null | | plain | | |
description | text | | not null | | extended | | |
person_name | character varying(512) | | not null | | extended | | |
Indexes:
"person_pkey" PRIMARY KEY, btree (id)
Access method: heap
test=#
test=#
test=# \d+ person_seq;
Sequence "public.person_seq"
Type | Start | Minimum | Maximum | Increment | Cycles? | Cache
--------+-------+---------+---------------------+-----------+---------+-------
bigint | 1 | 1 | 9223372036854775807 | 50 | no | 1
You can download this application from this link.
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