英文:
JPA Entities: how to check recursive parents
问题
我有一个简单的实体表示一个群组。
public class Group {Long id;String name;@JoinColumn(name = "idparent", nullable = true, referencedColumnName = "ID")@ManyToOne(targetEntity = Group.class, fetch = FetchType.EAGER, cascade = {}, optional = true)private Group parent;}
一个群组可以是一些群组的父群组。
在测试期间，我设置 A.parent = A，所以对象 A 陷入了递归。
是否有一个注解或者什么东西可以检查以下约束？
a.id != a.parent.id
英文:
I have a simple entity representing a group.
public class Group {Long id;String name;@JoinColumn(name = "idparent", nullable = true, referencedColumnName = "ID")@ManyToOne(targetEntity = Group.class, fetch = FetchType.EAGER, cascade = {}, optional = true)private Group parent;}
A group can be the parent of some groups.
During tests I set A.parent = A, so the A object fall in recursion.
Is there an annotation or something to check the following constraint?
a.id != a.parent.id
答案1
得分: 1
您可以创建一个自定义验证器和类级别的注解约束，使用验证 API 的 Constraint 注解绑定一个验证器类。
@Constraint(validatedBy = GroupConstraintValidator.class)@Target({TYPE })@Retention(RUNTIME)public @interface GroupConstraint {String message() default "Invalid TestA.";Class<?>[] groups() default {};Class<? extends Payload>[] payload() default {};}
创建一个验证器类，其中包含验证逻辑以检查 a.id != a.parent.id：
public class GroupConstraintValidator implements ConstraintValidator<GroupConstraint, Group>{@Overridepublic boolean isValid(Group object, ConstraintValidatorContext context) {if (!(object instanceof Group)) {throw new IllegalArgumentException("@CustomConstraint only applies to TestA");}Group group = (Group) object;if (group.getParent() != null && group.getParent().getId() == group.getId()) {return false;}return true;}}
将此约束应用于实体类 Group：
@Entity@GroupConstraintpublic class Group {@Id@GeneratedValue(strategy = GenerationType.AUTO)@Column(name= "ID", unique = true)private Long id;private String name;@JoinColumn(name = "IDPARENT", nullable = true, referencedColumnName = "ID")@ManyToOne(targetEntity = Group.class, fetch = FetchType.EAGER, cascade = {}, optional = true)private Group parent;}
现在，在生命周期回调期间，即当子引用自身时，验证提供程序应该抛出约束违规。
Group child = new Group();// 设置属性child.setParent(child);em.persist(child);
英文:
You can create a custom validator and class level annotation constraint, bind a validator class using the Constraint annotation of validation api.
@Constraint(validatedBy = GroupConstraintValidator.class)@Target({TYPE })@Retention(RUNTIME)public @interface GroupConstraint {String message() default "Invalid TestA.";Class<?>[] groups() default {};Class<? extends Payload>[] payload() default {};}
Create the validator class with the validation logic to check a.id != a.parent.id
public class GroupConstraintValidator implements ConstraintValidator<GroupConstraint, Group>{@Overridepublic boolean isValid(Group object, ConstraintValidatorContext context) {if (!(object instanceof Group)) {throw new IllegalArgumentException("@CustomConstraint only applies to TestA");}Group group = (Group) object;if (group.getParent() != null && group.getParent().getId() == group.getId()) {return false;}return true;}}
Apply this constraint to the entity class, Group.
@Entity@GroupConstraintpublic class Group {@Id@GeneratedValue(strategy = GenerationType.AUTO)@Column(name= "ID",unique = true)private Long id;private String name;@JoinColumn(name = "IDPARENT", nullable = true, referencedColumnName = "ID")@ManyToOne(targetEntity = Group.class, fetch = FetchType.EAGER, cascade = {}, optional = true)private Group parent;
Now the validation provider should through a constraint violation during lifecycle callbacks , that is when child references itself.
Group child = new Group();//set attributeschild.setParent(child);em.persist(child);
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