I need help for this case.
I have the following entities (I removed getters/setters/hash/toString for easy reading):
#Entity
public class Company implements Serializable{
#Id
private String id;
}
#Entity
public class Document implements Serializable{
#Id
private String id;
}
#Entity
#IdClass(Inbox.PK.class)
public class Inbox implements Serializable {
#Id
#ManyToOne(fetch = FetchType.LAZY)
private Company company;
#Id
#ManyToOne(fetch = FetchType.LAZY)
private Document document;
#OneToOne(fetch = FetchType.LAZY, mappedBy = "inbox")
private Invoice invoice;
public class PK implements Serializable{
private Company company;
private Document document;
}
}
First question is, should I use Company and Document types in PK class or String and String?
And here ... the headache :
#Entity
#IdClass(Invoice.PK.class)
public class Invoice implements Serializable {
#Id
#OneToOne(fetch = FetchType.LAZY, mappedBy = "invoice")
// #MapsId // ???
#JoinColumn(name = "companyId")//, referencedColumnName = "company")// ???
#JoinColumn(name = "documentId")//, referencedColumnName = "document")// ???
// #PrimaryKeyJoinColumn // ????
private Inbox inbox;
#Data
public static class PK implements Serializable {
// private Inbox inbox; // ???
// private String company,document; // ???
// private String companyId,documentId; // ???
// private String inboxCompanyId,inboxDocumentId; // ???
}
}
The PK of the Invoice Entity is also the FK to Inbox (I would like constraints to be generated), and the PK of Inbox is composed of two Entities (Company and Document).
I prefer to use IdClass rather EmbeddedId.
How could I configure Invoice to have, at the end, (company_id,document_id) as PK AND FK to Inbox?
I saw your question posted in upwork. I think you should use string + string type fields with #Id and #Column annotations in PK class.
Related
I have defined several JPA entities in a Spring Boot application.
#Entity
public class EntityA {
#Id
#Column(name = "id")
private String id
// ...
//....other fields
}
#Entity
public class EntityB {
#EmbeddedId
private MyEmbeddedId id;
// ....other fields
}
public class MyEmbeddedId {
#Column(name = "id_a")
private String idA;
#Column(name = "color")
private String color;
}
EntityA is self-sufifcient, EntityB has a composite key, one of whose constituent is primary key of EntityA(represented by column id_a). So I use embedded key feature here. There is a one-to-many relationship between EntityA and EntityB. An instance of EntityA can be mapped to multiple instances of EntityB.
Now, my objective is to fetch EntityA with all its associated EntityB.
How to go about mapping for this?
Try below Entity mappings,
#Entity
public class EntityA {
#Id
#Column(name = "id")
private String id
#OneToMany(mappedBy = "myEmbeddedId.idA",
cascade = CascadeType.ALL)
private Set<EntityB> entityB;
// ...
//....other fields
}
#Entity
public class EntityB {
#EmbeddedId
private MyEmbeddedId myEmbeddedId;
// ....other fields
}
public class MyEmbeddedId {
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name="id_a")
private EntityA idA;
#Column(name = "color")
private String color;
}
When you load EntityA, it will load all associated EntityB.
I have 3 entities named Student, Course, and StudentCourse as follows
#Entity
#Table(name = "student")
public class Student {
#Id
#GeneratedValue
private Integer id;
private String fullName;
}
#Entity
#Table(name = "course")
public class Course {
#Id
#GeneratedValue
private Integer id;
private String courseName;
}
#Entity
#Table(name = "student_course")
public class StudeCourse {
#Id
#GeneratedValue
private Integer studentId;
private Integer courseId;
private String extraColumn;
}
Restrictions: There are a couple of restrictions
One student can have only one course or no course at all
An extra entity (StudentCourse) is required to hold the relation with primary key as studentId only
StudentCourse is required and hence cannot be skipped
Get Student with Course entity if there is one registered
Help required in some magical code to retrieve Course of Student if there is one assigned.
#Entity
#Table(name = "student")
public class Student {
#Id
#GeneratedValue
private Integer id;
private String fullName;
// this is not correct code but just what I want
#JoinEntity(entity=StudentCourse, column="courseId")
private Course course;
}
StudentCourse is required and hence cannot be skipped
Ok, lets work with that.
One student can have only one course or no course at all
Implies that there is a #OneToOne relationship between Student and StudentCourse.
With the given information, the following entity model will work:
#Entity
#Table(name = "student")
public class Student {
#Column(name = "id")
#Id
#GeneratedValue
private Integer id;
#Column(name = "full_name")
private String full_name;
#OneToOne
#PrimaryKeyJoinColumn
private StudentCourse studentCourse;
}
#Entity
#Table(name = "student_course")
public class StudentCourse {
#Column(name = "id")
#Id
#GeneratedValue
private Integer id;
#JoinColumn(name = "id", nullable = false, updatable = false)
#MapsId
#OneToOne
private Student student;
#JoinColumn(name = "course_id")
#ManyToOne
private Course course;
...
}
A quick review:
#OneToOne on the Student.studentCourse field signifies that for every Student, there can be only one StudentCourse, and no more.
#PrimaryKeyJoinColumn on the Student.studentCourse field signifies that the value of the primary key column for Student should be used as the foreign key for the related entity, that is, StudentCourse.
#OneToOne on the StudentCourse.student field signifies that for every StudentCourse, there can be only one Student.
#MapsId on the StudentCourse.student field signifies that the primary key column for StudentCourse should be used as the join column for the association.
To check if a student has a course assigned, simply check if student.getStudentCourse() != null and then get the assigned course as student.getStudentCourse().getCourse().
I have three tables each mapping to one of these entities. The 'assigned' table acts as the relationship between 'users' and 'roles' with a foreign key to each table. How would I map this on my entities so that I can get a Set of EntityRoles from the UserEntity? I can't quite figure out how to make this work. Is this even possible?
#Entity
#Table(name = "users")
public class UserEntity {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name="user_id")
private long id;
#Column(name="user_username")
private String username;
#Column(name="user_password")
private String password;
#Column(name="user_email")
private String email;
//I want to be able to get a set of RoleEntities
#OneToMany(fetch = FetchType.LAZY, mappedBy = "id")
private Set<RoleEntity> roles;
}
#Entity
#Table(name = "assigned")
public class AssignedEntity implements Serializable {
#Id
//#Column(name = "assigned_role")
#ManyToOne(targetEntity = RoleEntity.class, fetch = FetchType.LAZY)
#JoinColumn(name = "fk_role")
private long roleId;
#Id
//#Column(name = "assigned_user")
#ManyToOne(targetEntity = UserEntity.class, fetch = FetchType.LAZY)
#JoinColumn(name = "fk_user")
private long userId;
}
#Entity
#Table(name = "roles")
public class RoleEntity implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name="role_id")
#OneToOne(fetch = FetchType.LAZY, mappedBy="roleId")
private long id;
#Column(name="role_name")
private String name;
}
You are using an incorrect/inconvenient mapping. Always keep things as simply as possible.
#Entity
#Table(name = "users")
public class User {
#Id
#GeneratedValue
private Long id;
#ManyToMany(fetch = FetchType.LAZY)
private List<Role> roles;
}
#Entity
#Table(name = "roles")
public class Role {
#Id
private Long id;
#Column
private String name;
}
A persistent provider will create a (valid) join table for you. You can specify the name of the join table using #JoinTable annotation. Also you will need to think about auto generation values of id for the Role entity: the roles table is something like a reference data table. So, probably, you will need to hardcode the id values.
To get user roles (in the persistent context):
user.getRoles()
I followed by tutorial : http://www.codejava.net/frameworks/hibernate/hibernate-one-to-one-mapping-with-foreign-key-annotations-example
I have following code:
#Entity
#Table(name = DomainConstant.TABLE_USER)
public class User{
#Id
#Column(name = DomainConstant.DOMAIN_USER_ID)
#GeneratedValue
private Long userId;
private UserActivationCode userActivationCode;
///////////////////// CONSTRUCTOR....
/// STANDARD GET AND SET....
#OneToOne(cascade = CascadeType.ALL)
#JoinColumn(name = DomainConstant.DOMAIN_ACTIVATION_LINK_ID)
public UserActivationCode getUserActivationCode() {
return userActivationCode;
}
}
#Entity
#Table(name = DomainConstant.TABLE_USER_ACTIVATON_LINK)
public class UserActivationCode {
#Id
#Column(name = DomainConstant.DOMAIN_ACTIVATION_LINK_ID)
#GeneratedValue
private Long userActivationCodeId;
#Column(name = DomainConstant.DOMAIN_ACTIVATION_DATE)
#Temporal(javax.persistence.TemporalType.DATE)
private Date date;
#Column(name = DomainConstant.DOMAIN_ACTIVATION_CODE)
private String code;
///////////////////// CONSTRUCTOR....
/// STANDARD GET AND SET....
}
When I save the User object it does not make record in UserActivationCode, why?
Like this:
User newUser = new User();
newUser.setUserActivationCode(new UserActivationCode("this is example"));
userDao.save(newUser);
I have record only in user table.
Can you tell me why?
Your problem is that you are mixing access types. In the User entity you have specified #Id on a field (private Long userId) whereas you have defined the join mapping on a property (the getter to UserActivationCode). If you specify the join mapping on the field, it should work as is.
#Entity
#Table(name = DomainConstant.TABLE_USER)
public class User{
#Id
#Column(name = DomainConstant.DOMAIN_USER_ID)
#GeneratedValue
private Long userId;
#OneToOne(cascade = CascadeType.ALL)
#JoinColumn(name = DomainConstant.DOMAIN_ACTIVATION_LINK_ID)
private UserActivationCode userActivationCode;
///////////////////// CONSTRUCTOR....
/// STANDARD GET AND SET....
public UserActivationCode getUserActivationCode() {
return userActivationCode;
}
}
For more information on access and access types, see Access, Java EE 7
I wrote an example for the code i am trying to implement, i get an error with Constraint "Student_Teacher_FK" already exists.
the #embiddable class has a foreign key that is created twice with current code.
#Entity
public class Teacher {
#Id
#GeneratedValue
private Long id;
#Column(name = "Name")
private String name;
}
#Entity
public class Student{
#Id
#GeneratedValue
private Long id;
#Column(name = "Name")
private String name;
}
#Embeddable
public class StudentList implements Serializable {
#ManyToMany
#JoinTable(name = "Student_Teacher",
joinColumns =
#JoinColumn(name = "Student_ID", referencedColumnName = "ID"),
inverseJoinColumns =
#JoinColumn(name = "Teacher_ID", referencedColumnName = "ID")
)
#ForeignKey(name = "Student_Teacher_FK", inverseName = "Teacher_Student_FK")
public List<Student> studentList = new ArrayList<Student>();
}
#Entity
public class HistoryTeacher extends Teacher {
#Embedded
#NotNull
private StudentList StudentList = new StudentList ();
}
#Entity
public class LangTeacher extends Teacher {
#Embedded
#NotNull
private StudentList StudentList = new StudentList ();
}
#Entity
public class RetiredTeacher extends Teacher {
// has no students
}
#embeddable : Defines a class whose instances are stored as an intrinsic part of an owning entity and share the identity of the entity (http://docs.oracle.com/javaee/6/api/javax/persistence/Embeddable.html)
As you are declaring it in 2 different entity, jpa will create associated association table (student-teacher) 2 times with associated fk, which is explicitely named, and so created 2 times too with the same name. Here is your error.
I don't think using #embeddable is appropriated for what you're intending to do. A student has is own existence and is not part of teacher itself (not an uml composition / black diamond) so it's not an embeddable entity. Student list should be held by teacher entity using a simple manyToMany association.