JPA @Column annotation to create comment/description

Question

I was wondering is it possible to create from jpa/hibernate annotation a database column description/comment like this:

ALTER TABLE tablename CHANGE status status INT(11) NOT NULL COMMENT 'sample description/comment';

It will be great functionality, but I cant find anything about this in JPA specification.

Maybe I should use @Column(columnDefinition="") property, but I dont have any clue. Please help

Answer 1

You can use @Comment annotation.

This annotation is introduced in hibernate 5.6.0 version(released at 2021-09-21), and Spring Boot 2.6(released at 2021-11-17) is using Hibernate 5.6

https://hibernate.atlassian.net/browse/HHH-4369\ https://github.com/hibernate/hibernate-orm/pull/3611

@Entity(name = "Person")
@javax.persistence.Table(name = TABLE_NAME)
@org.hibernate.annotations.Table(comment = TABLE_COMMENT, appliesTo = TABLE_NAME)
public static class TestEntity {

    @Id
    @GeneratedValue
    @Comment("I am id")
    private Long id;

    @Comment("I am name")
    @javax.persistence.Column(length = 50)
    private String name;

    @ManyToOne
    @JoinColumn(name = "other")
    @Comment("I am other")
    private TestEntity other;

}

Answer 2

Comment description already exists for Table annotations. We must use the Hibernate @Table annotation for that, complementary with the JPA @Table annotation.

For example :

@javax.persistence.Table( name = "Cat" )
@org.hibernate.annotations.Table( comment = "Table for cats" )
public class Cat {
...

Concerning the column's comment : It seems there is no equivalent, even in Hibernate 5.2 / JPA 2.1.

There has been an issue submitted a long time ago (2007) on this subject, but still unresolved : Support @Comment or column attribute on @Table and @Column. Abandoned since 2012 ?

I also found comment use in org.hibernate.dialect.Dialect :

/**
 * Does this dialect/database support commenting on tables, columns, etc?
 *
 * @return {@code true} if commenting is supported
 */
public boolean supportsCommentOn() {
    return false;
}

/**
 * Get the comment into a form supported for table definition.
 *
 * @param comment The comment to apply
 *
 * @return The comment fragment
 */
public String getTableComment(String comment) {
    return "";
}

/**
 * Get the comment into a form supported for column definition.
 *
 * @param comment The comment to apply
 *
 * @return The comment fragment
 */
public String getColumnComment(String comment) {
    return "";
}

For example PostgreSQL81Dialect supports it (supportsCommentOn() returns true).

It enables the use of the SQL command "COMMENT ON ...", like in PostgreSQL (https://www.postgresql.org/docs/current/static/sql-comment.html).
For example :

COMMENT ON TABLE my_schema.my_table IS 'Employee Information';
COMMENT ON COLUMN my_table.my_column IS 'Employee ID number';

It seems to be used there : org.hibernate.tool.schema.internal.StandardTableExporter#getSqlCreateStrings

The column's comment is extracted from the Hibernate Mapping with org.hibernate.mapping.Column#getComment.

Finally, If using Hibernate Tools and reverse engineering, the column's comment is extracted from JDBC DatabaseMetaData, with org.hibernate.cfg.reveng.BasicColumnProcessor#processBasicColumns.

-> String comment = (String) columnRs.get("REMARKS");