Sunday, 13 November 2022

Hibernate 6: Handle enum Using AttributeConverter

We can map an enum to a database column type by implementing AttributeConverter interface.

 

Step 1: Define Gender enum class.

 

Gender.java

public enum Gender {
    MALE('M'), FEMALE('F');

    private final char code;

    Gender(char code) {
        this.code = code;
    }

    public static Gender fromCode(char genderCode) {
        if (genderCode == 'F' || genderCode == 'f') {
            return FEMALE;
        }

        if (genderCode == 'M' || genderCode == 'm') {
            return MALE;
        }

        throw new UnsupportedOperationException("The code " + genderCode + " is not supported!");
    }

    public char getCode() {
        return code;
    }
}

Step 2: Implement AttributeConverter interface and override convertToDatabaseColumn, convertToEntityAttribute methods.

@Converter
public class GenderConverter implements AttributeConverter<Gender, Character> {

    @Override
    public Character convertToDatabaseColumn(Gender gender) {
        if (gender == null) {
            return null;
        }

        return gender.getCode();
    }

    @Override
    public Gender convertToEntityAttribute(Character genderCode) {
        if (genderCode == null) {
            return null;
        }

        return Gender.fromCode(genderCode);
    }
}

Step 3: Use the converter defined in step 2 while defining enum variables in the entity class.

 

@Entity
@Table(name = "person")
public class Person {

    @Id
    private Integer id;

    private String name;

    @Convert(converter = GenderConverter.class)
    private Gender gender;

    ......
    ......
}

 

Find the below working application.

 

Step 1: Create new maven project ‘hibernate-enum-attribute-converter-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-enum-attribute-converter-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 Gender enum.

 

Gender.java

 

package com.sample.app.enums;

public enum Gender {
    MALE('M'), FEMALE('F');

    private final char code;

    Gender(char code) {
        this.code = code;
    }

    public static Gender fromCode(char genderCode) {
        if (genderCode == 'F' || genderCode == 'f') {
            return FEMALE;
        }

        if (genderCode == 'M' || genderCode == 'm') {
            return MALE;
        }

        throw new UnsupportedOperationException("The code " + genderCode + " is not supported!");
    }

    public char getCode() {
        return code;
    }
}

 

Step 4: Define GenderConverter class.

 

GenderConverter.java
package com.sample.app.converters;

import com.sample.app.enums.Gender;

import jakarta.persistence.AttributeConverter;
import jakarta.persistence.Converter;

@Converter
public class GenderConverter implements AttributeConverter<Gender, Character> {

    @Override
    public Character convertToDatabaseColumn(Gender gender) {
        if (gender == null) {
            return null;
        }

        return gender.getCode();
    }

    @Override
    public Gender convertToEntityAttribute(Character genderCode) {
        if (genderCode == null) {
            return null;
        }

        return Gender.fromCode(genderCode);
    }
}

 

Step 5: Define Person entity class.

 

Person.java

 

package com.sample.app.entity;

import com.sample.app.converters.GenderConverter;
import com.sample.app.enums.Gender;

import jakarta.persistence.Convert;
import jakarta.persistence.Entity;
import jakarta.persistence.Id;
import jakarta.persistence.Table;

@Entity
@Table(name = "person")
public class Person {

    @Id
    private Integer id;

    private String name;

    @Convert(converter = GenderConverter.class)
    private Gender gender;

    public Person(Integer id, String name, Gender gender) {
        this.id = id;
        this.name = name;
        this.gender = gender;
    }

    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 Gender getGender() {
        return gender;
    }

    public void setGender(Gender gender) {
        this.gender = gender;
    }

}

 

Step 6: 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>

        <property name="hbm2ddl.auto">update</property>

        <!-- mappings for annotated classes -->
        <mapping class="com.sample.app.entity.Person" />

    </session-factory>

</hibernate-configuration>

 

Step 7: Define main application class.

 

App.java

 

package com.sample.app;

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;
import com.sample.app.enums.Gender;

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[]) {

        Person p1 = new Person(1, "Srinu", Gender.MALE);
        Person p2 = new Person(2, "Swetha", Gender.FEMALE);

        try (final Session session = SESSION_FACTORY.openSession()) {
            session.beginTransaction();

            session.persist(p1);
            session.persist(p2);

            session.getTransaction().commit();

        }

    }
}

Total project structure looks like below.



Run App.java, you will see below messages in the console.

Aug 12, 2022 12:31:23 PM org.hibernate.Version logVersion
INFO: HHH000412: Hibernate ORM core version 6.1.2.Final
Aug 12, 2022 12:31:23 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
WARN: HHH10001002: Using built-in connection pool (not intended for production use)
Aug 12, 2022 12:31:23 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001005: Loaded JDBC driver class: org.postgresql.Driver
Aug 12, 2022 12:31:23 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001012: Connecting with JDBC URL [jdbc:postgresql://127.0.0.1:5432/test]
Aug 12, 2022 12:31:23 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001001: Connection properties: {password=****, user=postgres}
Aug 12, 2022 12:31:23 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001003: Autocommit mode: false
Aug 12, 2022 12:31:23 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections <init>
INFO: HHH10001115: Connection pool size: 20 (min=1)
Aug 12, 2022 12:31:24 PM org.hibernate.engine.jdbc.dialect.internal.DialectFactoryImpl logSelectedDialect
INFO: HHH000400: Using dialect: org.hibernate.dialect.PostgreSQLDialect
Aug 12, 2022 12:31:24 PM org.hibernate.metamodel.internal.EntityInstantiatorPojoStandard resolveConstructor
INFO: HHH000182: No default (no-argument) constructor for class: com.sample.app.entity.Person (class must be instantiated by Interceptor)
Aug 12, 2022 12:31:24 PM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@1b7332a7] 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,
        gender char(1),
        name varchar(255),
        primary key (id)
    )
Aug 12, 2022 12:31:24 PM org.hibernate.engine.transaction.jta.platform.internal.JtaPlatformInitiator initiateService
INFO: HHH000490: Using JtaPlatform implementation: [org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform]
Hibernate: 
    insert 
    into
        person
        (gender, name, id) 
    values
        (?, ?, ?)

 

Query person table to confirm the same.

test=# SELECT * FROM person;
 id | gender |  name  
----+--------+--------
  1 | M      | Srinu
  2 | F      | Swetha
(2 rows)

You can download the application from this link.



  

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