Planned lessonJNR-028-L01

Mapping an entity

Lesson 1 of 8
Junior

On This Lesson 4 topics

In this lesson
Planned topics
Draft outline details
Practice

This lesson is planned. The outline below lists the topics it will cover. The full lesson has not been published yet.

In this lesson

turn a class into a table mapping.

Planned topics

@Entity marks a class as persistent; @Id marks its primary key.
JPA needs a no-argument constructor (protected is fine); entities are normal classes, not records.
@Table and @Column set names, length, and nullability; they should match the real schema.
Store enums with @Enumerated(EnumType.STRING), never the default ordinal (numbers break when you reorder).
Entities model the database, not the API: do not return them from controllers.

Draft outline details

Demonstration

java

@Entity
@Table(name = "product")
public class Product {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @Column(nullable = false, length = 120)
    private String name;
    @Enumerated(EnumType.STRING)
    private ProductStatus status;
    protected Product() {}
}

Check your understanding

Which enum mapping is safe?

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EnumType.STRING.

Practice

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