我正在 Play Framework 2.0.1 中探索 JPA 和 Ebean，以研究在本地关系数据库中生成的内容。在我的测试中，我使用的是 MySQL 的一个分支 MariaDB。
到目前为止，我已经能够使用模型中的 JPA 注释在数据库中成功生成表。我想确保我学会了如何设置一个与另一个实体具有 OneToOne 关系的实体，以及与另一个实体的 OneToMany 关系。
OneToOne：Employee有Address
OneToMany：Employee有Pet（S）
我设置了一个小型应用程序，它允许我快速填充表格、显示一些信息以及从表格中删除行。下面是那些想要查看我的设置的人的代码：
路线
GET / controllers.Application.index()
GET /add controllers.Application.addEmployee()
GET /delete/:id controllers.Application.deleteEmployee(id: Long)
GET /employee/:id controllers.Application.showEmployee(id: Long)
控制器
应用程序.java
public class Application extends Controller {
public static Result index() {
return ok(index.render("entry point"));
}
public static Result addEmployee() {
// Create an employee.
Employee employee = new Employee();
employee.firstName = "John";
employee.lastName = "Doe";
employee.salary = new BigDecimal(123456);
// Create an address for the employee.
Address address = new Address();
address.city = "West Chester";
address.country = "United States of America";
address.postalCode = "19380";
address.province = null;
address.street = "45 Jingleheimer Drive";
// Create pets for the employee.
Pet pet = new Pet();
pet.petString = "dog";
Pet pet2 = new Pet();
pet2.petString = "cat";
employee.address = address;
employee.pets.add(pet);
employee.pets.add(pet2);
employee.save();
return ok(index.render("added an employee"));
}
public static Result showEmployee(Long id) {
Employee e = Employee.get(id);
//String s = e.address.street;
return ok(employee.render(e));
}
public static Result deleteEmployee(Long id) {
Employee.delete(id);
return ok(index.render("deleted employee " + id));
}
}
楷模
雇员.java
@Entity
public class Employee extends Model {
@Id
public Long employee_id;
public String firstName;
public String lastName;
public BigDecimal salary;
@OneToOne(cascade=CascadeType.ALL)
@JoinColumn(name="owner_id")
public Address address;
@OneToMany(cascade=CascadeType.ALL)
@JoinColumn(name="owner_id", referencedColumnName="employee_id")
public List<Pet> pets;
public static Employee get(Long id) {
return find.byId(id);
}
public static void delete(Long id) {
find.byId(id).delete();
}
public static Finder<Long, Employee> find = new Finder<Long,Employee>(Long.class, Employee.class);
}
地址.java
@Entity
public class Address extends Model {
@Id
public Long address_id;
public String street;
public String city;
public String province;
public String country;
public String postalCode;
}
宠物.java
@Entity
public class Pet extends Model {
@Id
public Long pet_id;
public String petString;
}
意见
员工.scala.html
@(employee: models.Employee)
@import helper._
@main("employee view") {
<p>@employee.firstName</p>
<p>@employee.lastName</p>
<p>@employee.salary</p>
<p>@employee.address.country</p>
<p>@employee.pets(1).petString</p>
@for(pet <- employee.pets) {
<p>@pet.petString</p>
}
}
如果我使用 localhost:9000/employee/1 之类的 URL 呈现上面的视图，我会在浏览器中显示以下内容：
John
Doe
123456
cat
dog
cat
请注意，地址所在的国家/地区未显示。我还尝试在控制器中访问它并将其打印到打印 NULL 的命令窗口。
但是，我发现如果我在Address类中添加 getter，我可以在 scala 模板中检索它：
添加
public String getCity() {
return city;
}
...
到 Address.java 结果
John
Doe
123456
United States of America
cat
dog
cat
所以我可以设置一个地址并将其分配给一个员工（它显示在我的数据库中）。此外，正确删除员工会级联并删除数据库中的地址。同样，这适用于 Pet 类，即OneToMany. 那么为什么我需要添加 getter 来访问我的Address属性，而不是 forPet呢？我的一对一关系是否未在 Java 注释中正确设置？