Creating a model

In this project, we will create a REST API to see the list of user details where we can get a username, email ID, and contact number. So let's create a model of a user where the class name is UserModel.kt.

Here is the code of the model class:

@Entity
@Table(name="user_jpa")
@EntityListeners(AuditingEntityListener::class)
data class UserModel(
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    var id: Long = 0,

    @NotBlank
    @Column(name = "name")
    var name: String ?= null,

    @NotBlank
    @Column(name = "email")
    var email: String ?= null,

    @NotBlank
    @Column(name = "contact_number")
    var contact_number: String ?= null
)

Here, our UserModel class has the following fields:

• id: Primary key with auto increment
• name:  (NOT NULL field)
• email: (NOT NULL field)
• contact_number: (NOT NULL field)

Unlike JDBC, you don't need to create any table manually in your database. JPA will create a table using the UserModel. Let's look at how to create a table in our database using this UserModel object:

• @Entity: All your domain models must be annotated with this annotation. This annotation is used to mark the class as a persistent Java class.
• @Table: This annotation is used to provide the details of the table. The entity will be mapped by it.
• @Id: This is used to define the primary key.
• @GeneratedValue: This annotation is used to define the primary key generation strategy. In the preceding case, we have declared the primary key as an auto increment field.
• @NotBlank: This is used to verify that the annotated field is not null or empty.
• @Column: This is used to verify the properties of the column that will be mapped to the annotated field.