Precondition

To quickly preview Jimmer's main features, we need to provide several entities here as the basic assumption of all discussions in this section.

Status of Entities

tip

In Jimmer applications, the only thing that matters is the unified global ORM entity model.

The global entity model is finalized with the database design, irrelevant to specific query/modification business logics' requirements for interaction formats, and relatively stable.

As for what kind of DTO types each query/modification business needs to interact with, it is completely unimportant.

• Either no DTO is needed at all, e.g. Quick View/Query Arbitrary Shape/Exposing Features/Return Entities Directly.

• Or DTO types can be quickly generated through Object/DTO Conversion/DTO Language, making DTO extremely cheap.

Only the relatively stable entity model is important. So Jimmer is good at handling changing requirements.

UML Relationships Between Entities

Here we list three entity types: BookStore, Book, Author and TreeNode, as the basic assumptions for all discussions in the current section.

Entity Type Definitions

BookStore

Java

@Entity
public interface BookStore {

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

    String name();

    @Nullable
    String website();  

    @OneToMany(mappedBy = "store")
    List<Book> books();  
}

Kotlin

@Entity  
interface BookStore {

    @Id
    @@GeneratedValue(strategy = GenerationType.IDENTITY)  
    val id: Long  

    val name: String  

    val website: String?  

    @OneToMany(mappedBy = "store") 
    val books: List<Book>  
}

Book

Java

@Entity  
public interface Book {

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

    @Key  
    String name();

    @Key
    int edition();  

    BigDecimal price();  

    @Nullable  
    @ManyToOne  
    BookStore store();  

    @ManyToMany
    List<Author> authors();  
}

Kotlin

@Entity
interface Book {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)  
    val id: Long  

    @Key
    val name: String  

    @Key  
    val edition: Int  

    val price: BigDecimal

    @ManyToOne   
    val store: BookStore?  

    @ManyToMany
    val authors: List<Author>  
}

Author

Java

@Entity  
public interface Author {

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

    @Key
    String firstName();  

    @Key
    String lastName();   

    Gender gender();  

    @ManyToMany(mappedBy = "authors")
    List<Book> books();   
}

Kotlin

@Entity
interface Author {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    val id: Long  

    @Key 
    val firstName String   

    @Key
    val lastName: String   

    val gender: Gender  

    @ManyToMany(mappedBy = "authors")
    val books: List<Book>
}

Where Gender is a very simple enum type

Java

public enum Gender { MALE, FEMALE }

Kotlin

enum class Gender { MALE, FEMALE }