How to map Hibernate entity fields using camelCase to snake_case (underscore) database identifiers

You can achieve this using a custom Hibernate naming strategy.

All you need to do is to use the hibernate-types open-source project.

Hibernate 5.2 or later

You need to add the following Maven dependency:

<dependency>
    <groupId>com.vladmihalcea</groupId>
    <artifactId>hibernate-types-52</artifactId>
    <version>${hibernate-types.version}</version>
</dependency>

And set the following Hibernate configuration property:

<property name="hibernate.physical_naming_strategy"
          value="com.vladmihalcea.hibernate.type.util.CamelCaseToSnakeCaseNamingStrategy"
/>

Hibernate 5.0 and 5.1

You need to add the following Maven dependency:

<dependency>
    <groupId>com.vladmihalcea</groupId>
    <artifactId>hibernate-types-5</artifactId>
    <version>${hibernate-types.version}</version>
</dependency>

And set the following Hibernate configuration property:

<property name="hibernate.physical_naming_strategy"
          value="com.vladmihalcea.hibernate.type.util.CamelCaseToSnakeCaseNamingStrategy"
/>

Hibernate 4.3

You need to add the following Maven dependency:

<dependency>
    <groupId>com.vladmihalcea</groupId>
    <artifactId>hibernate-types-43</artifactId>
    <version>${hibernate-types.version}</version>
</dependency>

And set the following Hibernate configuration property:

<property name="hibernate.ejb.naming_strategy"
          value="com.vladmihalcea.hibernate.type.util.CamelCaseToSnakeCaseNamingStrategy"
/>

Hibernate 4.2 and 4.1

You need to add the following Maven dependency:

<dependency>
    <groupId>com.vladmihalcea</groupId>
    <artifactId>hibernate-types-4</artifactId>
    <version>${hibernate-types.version}</version>
</dependency>

And set the following Hibernate configuration property:

<property name="hibernate.ejb.naming_strategy"
          value="com.vladmihalcea.hibernate.type.util.CamelCaseToSnakeCaseNamingStrategy"
/>

Testing time

Assuming you have the following entities:

@Entity(name = "BookAuthor")
public class BookAuthor {
 
    @Id
    private Long id;
 
    private String firstName;
 
    private String lastName;
 
    //Getters and setters omitted for brevity
}
 
@Entity(name = "PaperBackBook")
public class PaperBackBook {
 
    @Id
    @GeneratedValue(
        strategy = GenerationType.SEQUENCE
    )
    private Long id;
 
    @NaturalId
    private String ISBN;
 
    private String title;
 
    private LocalDate publishedOn;
 
    @ManyToOne(fetch = FetchType.LAZY)
    private BookAuthor publishedBy;
 
    //Getters and setters omitted for brevity
}

When using the CamelCaseToSnakeCaseNamingStrategy custom naming strategy, Hibernate is going to generate the following database schema using the hbm2ddl tool:

CREATE SEQUENCE hibernate_sequence
START WITH 1 INCREMENT BY 1
 
CREATE TABLE book_author (
    id          BIGINT NOT NULL,
    first_name  VARCHAR(255),
    last_name   VARCHAR(255),
    PRIMARY KEY (id)
)
 
CREATE TABLE paper_back_book (
    id              BIGINT NOT NULL,
    isbn            VARCHAR(255),
    published_on    DATE, 
    title           VARCHAR(255),
    published_by_id BIGINT, 
    PRIMARY KEY (id)
)

Cool, right?

I was experiencing the same problem in a Spring boot application, I tried adding the above Hibernate config to the spring properties file with no success, added it as a java bean, again with no success.

I am using Hibernate Properties object, adding the hibernate configuration within this solved my issue:

    protected Properties buildHibernateProperties() {
        Properties hibernateProperties = new Properties();
        hibernateProperties.setProperty("hibernate.implicit_naming_strategy", SpringImplicitNamingStrategy.class.getName());
        hibernateProperties.setProperty("hibernate.physical_naming_strategy", SpringPhysicalNamingStrategy.class.getName());

        return hibernateProperties;
    }

From Hibernate 5.5.4.Final, CamelCaseToUnderscoresNamingStrategy has been introduced, the new strategy is the equivalent of the Spring SpringPhysicalNamingStrategy.

The CamelCaseToUnderscoresNamingStrategy replaces all dots with underscores, all camel casing with underscores and generates all table names in lower case.

For example, the LineItem entity will be mapped to the line_item table.

import org.hibernate.cfg.DefaultNamingStrategy;
import org.hibernate.cfg.ImprovedNamingStrategy;

public class NamingStratagyTest {
    public static void main(String[] args) {
        String colName = DefaultNamingStrategy.INSTANCE.columnName("UserName");
        System.out.println(colName); // UserName
        colName = ImprovedNamingStrategy.INSTANCE.columnName("UserName");
        System.out.println(colName);// user_name
    }
}

There you go, choose the naming strategy that suits your need.