Hibernate JPA @ColumnTransformer Example

@ColumnTransformer

The @ColumnTransformer annotation is used to customize how a given column value is read from or written into the database.

ColumnTransformer
Custom SQL expression used to read the value from and write a value to a column. Use for direct object loading/saving as well as queries. The write expression must contain exactly one '?' placeholder for the value. For example: read="decrypt(credit_card_num)" write="encrypt(?)"

@ColumnTransformer example
@Entity(name = "Employee")
public static class Employee {

@Id
private Long id;

@NaturalId
private String username;

@Column(name = "pswd")
@ColumnTransformer(
read = "decrypt( 'AES', '00', pswd  )",
write = "encrypt('AES', '00', ?)"
)
private String password;

private int accessLevel;

@ManyToOne(fetch = FetchType.LAZY)
private Department department;

@ManyToMany(mappedBy = "employees")
private List<Project> projects = new ArrayList<>();

//Getters and setters omitted for brevity
}
If a property uses more than one column, you must use the forColumn attribute to specify which column the @ColumnTransformer read and write expressions are targeting.

Example : @ColumnTransformer forColumn attribute usage
@Entity(name = "Savings")
public static class Savings {

@Id
private Long id;

@Embedded
@ColumnTransformer(
forColumn = "money",
read = "money / 100",
write = "? * 100"
)
private MonetaryAmount wallet;

//Getters and setters omitted for brevity

}