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

Question

I have database fields in underscore. I have entity fields in camelcase. I can't change either of those.

Is there something, maybe a class level annotation I can use to default entity column name annotations to the camelcase equivalent?

for example, I have an entity like this:

@Entity
public class AuthorisationEntity {

    @Column(name = "non_recoverable")
    private BigDecimal nonRecoverable;

    @Column(name = "supplier_recoverable")
    private BigDecimal supplierRecoverable;

    @Column(name = "refund_amount")
    private BigDecimal refundAmount;

}

I dream of this:

@Entity
@DatabaseIsUnderscoreAndThisAnnotationConvertsThemToCamelCaseByDefault
public class AuthorisationEntity {

    private BigDecimal nonRecoverable;

    private BigDecimal supplierRecoverable;

    private BigDecimal refundAmount;

}

Answer 1

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?