There are situations, where you want to calculate a value from other entity properties by applying some computations. You can do this with the help of @Formula annotation.
Example
@Entity
@Table(name = "account")
public class Account {
@Id
private Integer accountId;
private Double principal;
private Double timeInYears;
private Double rateOfIntrest;
@Formula(value = "(principal * timeInYears * rateOfIntrest ) /100")
private Double interestToPay;
//Getters and setters omitted for brevity
}
When loading the Account entity, Hibernate is going to calculate the interestToPay property using the configured @Formula.
Find the below working application.
Step 1: Create new maven project ‘hibernate-formula-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-formula-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 Account entity class.
Account.java
package com.sample.app.entity;
import org.hibernate.annotations.Formula;
import jakarta.persistence.Entity;
import jakarta.persistence.Id;
import jakarta.persistence.Table;
@Entity
@Table(name = "account")
public class Account {
@Id
private Integer accountId;
private Double principal;
private Double timeInYears;
private Double rateOfIntrest;
@Formula(value = "(principal * timeInYears * rateOfIntrest ) /100")
private Double interestToPay;
public Account(Integer accountId, Double principal, Double timeInYears, Double rateOfIntrest) {
this.accountId = accountId;
this.principal = principal;
this.timeInYears = timeInYears;
this.rateOfIntrest = rateOfIntrest;
}
public Integer getAccountId() {
return accountId;
}
public void setAccountId(Integer accountId) {
this.accountId = accountId;
}
public Double getPrincipal() {
return principal;
}
public void setPrincipal(Double principal) {
this.principal = principal;
}
public Double getRateOfIntrest() {
return rateOfIntrest;
}
public void setRateOfIntrest(Double rateOfInrest) {
this.rateOfIntrest = rateOfInrest;
}
public Double getTimeInYears() {
return timeInYears;
}
public void setTimeInYears(Double timeInYears) {
this.timeInYears = timeInYears;
}
public Double getInterestToPay() {
return interestToPay;
}
public void setInterestToPay(Double interestToPay) {
this.interestToPay = interestToPay;
}
}
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.Account" />
</session-factory>
</hibernate-configuration>
Step 5: 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.Account;
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[]) {
Account account = new Account(1, 1000000.0, 2.3, 2.0);
try (final Session session = SESSION_FACTORY.openSession()) {
session.beginTransaction();
session.persist(account);
// Since entity is cached on persist, lets flush and refresh the entity to
// refetch the data from database.
session.flush();
session.refresh(account);
session.getTransaction().commit();
Account persistedAccount = session.find(Account.class, 1);
System.out.println("prinicpal : " + persistedAccount.getPrincipal());
System.out.println("timeInYears : " + persistedAccount.getTimeInYears());
System.out.println("rateOfInrest : " + persistedAccount.getRateOfIntrest());
System.out.println("interestToPay : " + persistedAccount.getInterestToPay());
}
}
}
Total project structure looks like below.
Run App.java, you will see below messages in console.
Aug 09, 2022 8:54:03 PM org.hibernate.Version logVersion
INFO: HHH000412: Hibernate ORM core version 6.1.2.Final
Aug 09, 2022 8:54:03 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
WARN: HHH10001002: Using built-in connection pool (not intended for production use)
Aug 09, 2022 8:54:03 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001005: Loaded JDBC driver class: org.postgresql.Driver
Aug 09, 2022 8:54:03 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 8:54:03 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001001: Connection properties: {password=****, user=postgres}
Aug 09, 2022 8:54:03 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001003: Autocommit mode: false
Aug 09, 2022 8:54:03 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections <init>
INFO: HHH10001115: Connection pool size: 20 (min=1)
Aug 09, 2022 8:54:04 PM org.hibernate.engine.jdbc.dialect.internal.DialectFactoryImpl logSelectedDialect
INFO: HHH000400: Using dialect: org.hibernate.dialect.PostgreSQLDialect
Aug 09, 2022 8:54:04 PM org.hibernate.metamodel.internal.EntityInstantiatorPojoStandard resolveConstructor
INFO: HHH000182: No default (no-argument) constructor for class: com.sample.app.entity.Account (class must be instantiated by Interceptor)
Hibernate:
drop table if exists account cascade
Aug 09, 2022 8:54:04 PM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@41dc0598] 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 8:54:04 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: SQL Warning Code: 0, SQLState: 00000
Aug 09, 2022 8:54:04 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: table "account" does not exist, skipping
Hibernate:
create table account (
accountId integer not null,
principal float(53),
rateOfInrest float(53),
timeInYears float(53),
primary key (accountId)
)
Aug 09, 2022 8:54:04 PM org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@3e4e4c1] 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 8:54:04 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
account
(principal, rateOfInrest, timeInYears, accountId)
values
(?, ?, ?, ?)
Hibernate:
select
a1_0.accountId,
(a1_0.principal * a1_0.timeInYears * a1_0.rateOfInrest ) /100,
a1_0.principal,
a1_0.rateOfInrest,
a1_0.timeInYears
from
account a1_0
where
a1_0.accountId=?
prinicpal : 1000000.0
timeInYears : 2.3
rateOfInrest : 2.0
interestToPay : 46000.0
Data in PostgresSQL is given below.
test=# \d+ account;
Table "public.account"
Column | Type | Collation | Nullable | Default | Storage | Compression | Stats target | Description
---------------+------------------+-----------+----------+---------+---------+-------------+--------------+-------------
accountid | integer | | not null | | plain | | |
principal | double precision | | | | plain | | |
rateofintrest | double precision | | | | plain | | |
timeinyears | double precision | | | | plain | | |
Indexes:
"account_pkey" PRIMARY KEY, btree (accountid)
Access method: heap
test=#
test=# SELECT * FROM account;
accountid | principal | rateofintrest | timeinyears
-----------+-----------+---------------+-------------
1 | 1000000 | 2 | 2.3
(1 row)
You can download complete working application from this link.
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