MappedSuperclass

Basic Usage

org.babyfish.jimmer.sql.MappedSuperclass is used to provide abstract super types that can be inherited by entities.

The super type itself is not an entity, but can be inherited by multiple entity types to avoid duplicate declaration of the same properties in multiple entities.

Let's look at an example. First define the super type:

Java

BaseEntity.java

@MappedSuperclass
public interface BaseEntity {

    LocalDateTime createdTime();

    @ManyToOne
    User createdBy();

    LocalDateTime modifiedTime();

    @ManyToOne
    User modifiedBy();
}

Kotlin

BaseEntity.kt

@MappedSuperclass
interface BaseEntity {

    val createdTime: LocalDateTime

    @ManyToOne
    val createdBy: User

    val modifiedTime: LocalDateTime

    @ManyToOne
    val modifiedBy: User
}

Other entities can inherit it:

• BookStore

  Java

  BookStore.java

  @Entity
  public interface BookStore extends BaseEntity {
  
      ...Omit other code...
  }

  Kotlin

  BookStore.kt

  @Entity
  interface BookStore : BaseEntity {
  
      ...Omit other code...
  }

• Book

  Java

  Book.java

  @Entity
  public interface Book extends BaseEntity {
  
      ...Omit other code...
  }

  Kotlin

  Book.kt

  @Entity
  interface Book : BaseEntity {
  
      ...Omit other code...
  }

• Author

  Java

  Author.java

  @Entity
  public interface Author extends BaseEntity {
  
      ...Omit other code...
  }

  Kotlin

  Author.kt

  @Entity
  interface Author : BaseEntity {
  
      ...Omit other code...
  }

Multiple Inheritance

Types decorated with MappedSuperclass support multiple inheritance. Other types can inherit from multiple MappedSuperclass super types.

Add a new abstract interface TenantAware to be inherited by all multi-tenant entities:

Java

TenantAware.java

@MappedSuperclass  
public interface TenantAware {

    String tenant();
}

Kotlin

TenantAware.kt

interface TenantAware {

    val tenant: String
}

Java

Book.java

@Entity
public interface Book extends BaseEntity, TenantAware {

    ...Omit other code...
}

Kotlin

Book.kt

@Entity
interface Book : BaseEntity, TenantAware {

    ...Omit other code...
}

Modify Book to inherit not only BaseEntity but also TenantAware.

tip

The role of @MapperSuperclass is not just to reduce duplicate code, it can also cooperate with two other functions:

• Global Filters
• Interceptors

When used in cooperation with them, multiple inheritance can provide good flexibility.