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Setting a default value for a createdDateTime field in a JPA entity is a common requirement in many applications. It ensures that every new record automatically has a creation timestamp. This can be handled in both JPA (Java code) and PostgreSQL (database schema). Let’s walk through the best way to do it using @PrePersist and PostgreSQL’s default CURRENT_TIMESTAMP.

1. Define the Entity Class with @PrePersist

In the JPA entity, we use the @PrePersist lifecycle hook to automatically assign the current date and time when an entity is saved for the first time.

java

import javax.persistence.*;
import java.time.LocalDateTime;

@Entity
public class MyEntity {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "created_date_time", nullable = false, updatable = false)
    private LocalDateTime createdDateTime;

    @PrePersist
    protected void onCreate() {
        this.createdDateTime = LocalDateTime.now();
    }

    // Getters and setters
    public Long getId() {
        return id;
    }

    public LocalDateTime getCreatedDateTime() {
        return createdDateTime;
    }

    public void setCreatedDateTime(LocalDateTime createdDateTime) {
        this.createdDateTime = createdDateTime;
    }
}

2. Add a Default Value in PostgreSQL

Even though JPA handles the default timestamp at the Java level, it's good practice to set a default value in the database as well — especially to cover cases where data is inserted directly into the database.

Here’s how you can alter the table to add a default value for the created_date_time column:

sql

ALTER TABLE my_entity
ADD COLUMN created_date_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP NOT NULL;

This ensures that even if JPA doesn't set the value, PostgreSQL will.

3. Combining JPA and PostgreSQL for Robustness

By using both @PrePersist in the entity and setting a default in PostgreSQL, you cover:

• ORM-based inserts (@PrePersist sets the time).
• Direct SQL inserts (PostgreSQL default kicks in).

4. Full Spring Boot Example

Dependencies (pom.xml):

xml

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
    <dependency>
        <groupId>org.postgresql</groupId>
        <artifactId>postgresql</artifactId>
        <scope>runtime</scope>
    </dependency>
</dependencies>

application.properties:

properties

spring.datasource.url=jdbc:postgresql://localhost:5432/mydatabase
spring.datasource.username=myusername
spring.datasource.password=mypassword
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true

Repository:

java

import org.springframework.data.jpa.repository.JpaRepository;

public interface MyEntityRepository extends JpaRepository<MyEntity, Long> {
}

Controller:

java

import org.springframework.web.bind.annotation.*;
import org.springframework.beans.factory.annotation.Autowired;
import java.util.List;

@RestController
@RequestMapping("/entities")
public class MyEntityController {

    @Autowired
    private MyEntityRepository repository;

    @PostMapping
    public MyEntity create(@RequestBody MyEntity entity) {
        return repository.save(entity);
    }

    @GetMapping
    public List<MyEntity> getAll() {
        return repository.findAll();
    }
}

Conclusion

To reliably set a default createdDateTime in JPA with PostgreSQL:

• Use @PrePersist in the entity class to set the timestamp before saving.
• Define a DEFAULT CURRENT_TIMESTAMP in the PostgreSQL schema to back it up.
• This ensures consistent behavior whether your data is inserted via JPA or SQL.

This is a solid best-practice approach for audit fields like createdDateTime.