Entity classes

Entity classes correspond to database tables or query result sets.

Entity definition

The following code snippet shows how to define an entity:

@Entity
public class Employee {
    ...
}

An entity class can inherit other entity class.

The following code snippet shows how to inherit other entity class:

@Entity
public class SkilledEmployee extends Employee {
    ...
}

Note

In Java 14 and later version, you can annotate records with @Entity:

@Entity
public record Employee(...) {
}

In the case, the entity is recognize as Immutable even though the immutable property of @Entity is false.

Entity listeners

Entity listeners work before/after Doma issues the database modification statements - INSERT, DELETE and UPDATE.

The following code snippet shows how to define an entity listener:

public class EmployeeEntityListener implements EntityListener<Employee> {
    ...
}

To use the entity listener, specify it to the listener property within the @Entity annotation:

@Entity(listener = EmployeeEntityListener.class)
public class Employee {
    ...
}

An entity subclass inherits parent`s entity listener.

Naming convention

Naming convention maps the names between:

  • the database tables and the Java entity classes

  • the database column and the Java entity fields

The following code snippet shows how to apply the naming convention to an entity:

@Entity(naming = NamingType.SNAKE_UPPER_CASE)
public class EmployeeInfo {
    ...
}

When the name property within the @Table or @Column annotation is explicitly specified, the naming convention is ignored.

An entity subclass inherits parent’s naming convention.

Immutable

An entity class can be immutable.

The following code snippet shows how to define an immutable entity:

@Entity(immutable = true)
public class Employee {
    @Id
    final Integer id;
    final String name;
    @Version
    final Integer version;

    public Employee(Integer id, String name, Integer version) {
        this.id = id;
        this.name = name;
        this.version = version;
    }
    ...
}

The immutable property within the @Entity annotation must be true. The persistent field must be final.

An entity subclass inherits parent’s immutable property.

Table

You can specify the corresponding table name with the @Table annotation:

@Entity
@Table(name = "EMP")
public class Employee {
    ...
}

Without the @Table annotation, the table name is resolved by Naming Convention.

Field definition

By default, the fields are persistent and correspond to the database columns or result set columns.

The field type must be one of the following:

The following code snippet shows how to define a filed:

@Entity
public class Employee {
    ...
    Integer employeeId;
}

Column

You can specify the corresponding column name with the @Column annotation:

@Column(name = "ENAME")
String employeeName;

To exclude fields from INSERT or UPDATE statements, specify false to the insertable or updatable property within the @Column annotation:

@Column(insertable = false, updatable = false)
String employeeName;

Without the @Column annotation, the column name is resolved by Naming Convention.

Note

When the filed type is Embeddable classes, you cannot specify the @Column annotation to the field.

Id

The database primary keys are represented with the @Id annotation:

@Id
Integer id;

When there is a composite primary key, use the @Id annotation many times:

@Id
Integer id;

@Id
Integer id2;

Note

When the filed type is Embeddable classes, you cannot specify the @Id annotation to the field.

Id generation

You can instruct Doma to generate id values automatically using the @GeneratedValue annotation.

The field type must be one of the following:

  • the subclass of java.lang.Number

  • Domain classes, whose value type is the subclass of java.lang.Number

  • java.util.Optional, whose element is either above types

  • OptionalInt

  • OptionalLong

  • OptionalDouble

  • the primitive types for number

Note

The generated values are assign to the field only when the field is either null or less than 0. If you use one of the primitive types as filed type, initialize the field with tha value that is less than 0, such as -1.

Id generation by IDENTITY

To generate values using the RDBMS IDENTITY function, specify the GenerationType.IDENTITY enum value to strategy property within the @GeneratedValue:

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

In advance, define the database primary key as IDENTITY.

Warning

All RDBMS doesn’t support the IDENTITY function.

Id generation by SEQUENCE

To generate values using the RDBMS SEQUENCE, specify the GenerationType.SEQUENCE enum value to strategy property within the @GeneratedValue annotation. And use the @SequenceGenerator annotation:

@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE)
@SequenceGenerator(sequence = "EMPLOYEE_SEQ")
Integer id;

In advance, define the SEQUENCE in the database. The SEQUENCE definitions such as the name, the allocation size and the initial size must correspond the properties within the @SequenceGenerator annotation.

Warning

All RDBMS doesn’t support the SEQUENCE.

Id generation by TABLE

To generate values using the RDBMS TABLE, specify the GenerationType.TABLE enum value to strategy property within the @GeneratedValue annotation. And use the @TableGenerator annotation:

@Id
@GeneratedValue(strategy = GenerationType.TABLE)
@TableGenerator(pkColumnValue = "EMPLOYEE_ID")
Integer id;

In advance, define the TABLE in the database. The TABLE`s definition must correspond to the properties within the @TableGenerator annotation. For example, the DDL should be following:

CREATE TABLE ID_GENERATOR(PK VARCHAR(20) NOT NULL PRIMARY KEY, VALUE INTEGER NOT NULL);

You can change the table name and the column names using the properties within the @TableGenerator annotation.

Version

The version fields for optimistic locking are represented with the @Version annotation.

The field type must be one of the following:

  • the subclass of java.lang.Number

  • Domain classes, whose value type is the subclass of java.lang.Number

  • java.util.Optional, whose element is either above types

  • OptionalInt

  • OptionalLong

  • OptionalDouble

  • the primitive types for number

@Version
Integer version;

Note

When the filed type is Embeddable classes, you cannot specify the @Version annotation to the field.

Tenant Id

The tenant id fields are represented with the @TenantId annotation. The column corresponding to the annotated field is included in the WHERE clause of UPDATE and DELETE statements.

@TenantId
String tenantId;

Note

When the filed type is Embeddable classes, you cannot specify the @TenantId annotation to the field.

Transient

If an entity has fields that you don’t want to persist, you can annotate them using @Transient:

@Transient
List<String> nameList;

OriginalStates

If you want to include only changed values in UPDATE statements, you can define fields annotated with @OriginalStates. The fields can hold the original values that were fetched from the database.

Doma uses the values to know which values are changed in the application and includes the only changed values in UPDATE statements.

The following code snippet shows how to define original states:

@OriginalStates
Employee originalStates;

The field type must be the same as the entity type.

Method definition

There are no limitations in the use of methods.

Example

Instantiate the Employee entity class and use its instance:

Employee employee = new Employee();
employee.setEmployeeId(1);
employee.setEmployeeName("SMITH");
employee.setSalary(new BigDecimal(1000));