I am using spring boot and spring data rest and have two entities, Exam and Subject which are defined as follows:
public class Exam {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name="exam_id")
Integer examId;
#Column(name="exam_name")
String examName;
#ManyToMany(mappedBy = "exams")
Set<Subject> subjects = new HashSet<>(0);
}
public class Subject {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "subject_id")
Integer subjectId;
#Column(name = "subject_name")
String subjectName;
#ManyToMany
#JoinTable(
name = "subject_exam",
joinColumns = {#JoinColumn(name = "subject_id", updatable = false, nullable = false)},
inverseJoinColumns = {#JoinColumn(name = "exam_id", updatable = false, nullable = false)}
)
Set<Exam> exams = new HashSet<>(0);
}
Now I have defined projection for subject as follow:
#Projection(name="detail", types={Subject.class})
public interface SubjectDetailProjection {
Integer getSubjectId();
String getSubjectName();
Set<ExamDetailProjection> getExams();
}
Detail projection for exam has also been defined in the same manner.
Now I am getting infinite recursion when calling api for this projection. How can I avoid this issue?
You have to delete, in your ExamDetailProjection, your referente to Subject.
You must to define one package of projections to your Subject and another package of projections to your Exams.
The exam projection will have a subject projection without reference to exam and the same in the other direction.
Related
I started to learn spring data rest. I'm doing PUT operation and it's not working for the nested objects for ManyToMany relationship, whereas it works fine for OneToMany relation.
Entities structures:
#Table(name="CONFIG_DTLS",schema = "app_txn")
#Entity
public class Config {
#Id
#GenericGenerator(name = "UUIDGenerator", strategy = "uuid2")
#GeneratedValue(generator = "UUIDGenerator")
#Column(name = "ID", updatable = false, nullable = false)
private UUID id;
#Column(name = "NAME", nullable = false, length = 75)
private String name;
/*Unable to replace the data in the MBR_CONFIG_MAPPING table in the put operation.
When the control comes to #HandleBeforeSave annotated method in PUT operation,
the request data contains the existing Member info instead of the one which i'm passing in the PUT request body */
#ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE},fetch = FetchType.EAGER)
#JoinTable(schema = "app_txn", name = "MBR_CONFIG_MAPPING",
joinColumns ={#JoinColumn(name="CONFIG_ID",referencedColumnName = "ID")},
inverseJoinColumns = {#JoinColumn(name="MBR_ID",referencedColumnName = "ID")}
)
private Set<Member> members;
//able to replace the notifications completely in PUT operation
#OneToMany(cascade = CascadeType.ALL,fetch = FetchType.EAGER)
#JoinColumn(name = "CONFIG_ID",referencedColumnName = "ID")
private Set<Notification> notifications;
}
Member.java
#Table(name="MBR_DTLS",schema = "app_txn")
#Entity
public class Member {
#Id
#GenericGenerator(name = "UUIDGenerator", strategy = "uuid2")
#GeneratedValue(generator = "UUIDGenerator")
#Column(name = "ID", updatable = false, nullable = false)
private UUID id;
#Column(name = "OTHER_MBR_DATA", updatable = false)
private String otherMbrData;
}
Notification.java
#Table(name="NOTIFICATIONS",schema = "app_txn")
#Entity
public class Notification {
#Id
#GenericGenerator(name = "UUIDGenerator", strategy = "uuid2")
#GeneratedValue(generator = "UUIDGenerator")
#Column(name = "ID", updatable = false, nullable = false)
private UUID id;
#Column(name="LEVEL")
private String level;
#Column(name="EMAIL")
private String email;
}
Interfaces:
#RepositoryRestResource(collectionResourceRel = "configs", path="configs")
public interface ConfigRepo extends PagingAndSortingRepository<Config,UUID> {
}
#RepositoryRestResource(exported=false) // don't want to users to manipulate it directly.
public interface MemberRepo extends PagingAndSortingRepository<Member,Object> {
}
Here I don't want to add or modify anything in the MBR_DTLS table as it is loaded by another backend process. I want to update only the mapping details MBR_CONFIG_MAPPING table whenever user does the PUT/update operation. POST/create operation is working fine. Please share your thoughts on how to fix this and if you have any questions add it in the comment section.
PS: I referred some links online but that does not help much - Spring Data REST - PUT request does not work properly since v.2.5.7
Im new in Java Spring and I'm stuck at this point here for a while:
I have an entity model like this:
Entity Relation now
A channellist contains many channels. A channel can be assigned to many channellists. I have setup my code that this works fine. Now I would like to add a property "sort" to my channels, so I would be able to order the channels for every specific channellist in a way I would like to. From the database relation model I know I have to store this information in the joining table "Channellist_Channel".
MY PROBLEM IS: I dont understand how I'm able asign this property to my Entity "Channel" so that every Channel has a "sort"-value depending on the context of the channellist. I read for this case, I have to add a new Entity which will represent the join table "Channellist_Channel" and add the property "sort" there. But the puzzle in my head is just not complete to do it :/
Here are my two entitys Channellist and Channel
CHANNELLIST:
#Entity
#Table(name = "channellist", schema = "stream")
public class Channellist {
#Id
#Column(name = "ID")
private int id;
#Column(name = "DISPLAYNAME")
private String displayName;
#ManyToMany
#JoinTable(
schema = "stream",
name = "Channellist_Channel",
joinColumns = #JoinColumn(name = "channellist_id"),
inverseJoinColumns = #JoinColumn(name = "channel_id")
)
private Set<Channel> channels;
//Constructors...
//Getter Setter...
CHANNEL:
#Entity
#Table(name = "channel", schema = "stream")
public class Channel {
#Id
#Column(name = "id")
private String id;
#Column(name = "display_name")
private String displayName;
#Column(name = "type")
private int type;
#Column(name = "logo_url")
private String logoUrl;
#Column(name = "stream_url")
private String streamUrl;
#OneToMany(mappedBy = "channelId", fetch = FetchType.LAZY)
#OrderBy(value = "timeStart ASC")
private Set<ChannelEpg> programs;
#JsonIgnore
#ManyToMany
#JoinTable(
schema = "stream",
name = "Channellist_Channel",
joinColumns = #JoinColumn(name = "channel_id"),
inverseJoinColumns = #JoinColumn(name = "channellist_id")
)
private Set<Channellist> channellists;
//Constructors...
//Getters Setters...
My JSON Response from "GetAllChannellists: Please Ignore the TAG "programs" under "channels". Its not relevant for my problem.
JSON RESPONSE:
[
{"id":1,
"displayName":"Standard",
"channels":[
{"id":"344143862749137509158c22d1606ad5",
"displayName":"KiKa",
"type":0,
"logoUrl":"https://example.de/test/kika.png",
"streamUrl":"https://example.de/test/kika.m3u8",
"programs":[
{"channelId":"344143862749137509158c22d1606ad5",
"timeStart":"2022-08-09T11:30:00.000+00:00",
"timeEnd":"2022-08-09T11:40:00.000+00:00",
"title":"logo!",
"subTitle":null,
"description":"a verry long description, no one cares"},
{"channelId":"344143862749137509158c22d1606ad5",
"timeStart":"2022-08-09T11:40:00.000+00:00",
"timeEnd":"2022-08-09T12:10:00.000+00:00",
"title":"Tiere bis unters Dach",
"subTitle":"Jojo, der Held",
"description":"another long description, no one cares"},
[...]
{"id":2,
"displayName":"Deluxe",
"channels":[
[...]
My goal is it to make it look like this:
[
{"id":1,
"displayName":"Standard",
"channels":[
{"id":"344143862749137509158c22d1606ad5",
"displayName":"KiKa",
"sort":21,
"type":0,
"logoUrl":"https://example.de/test/kika.png",
"streamUrl":"https://example.de/test/kika.m3u8",
When I make changes to one attribute of an entity, it also somehow gets changed for every other entity that uses that entity. I have three entities as you can see below.
Students and courses need to have a many-to-many relationship between them and the course needs to have a one-to-many relationship with course lectures.
When I make changes to courses or course lectures that belong to a specific student by doing #Transactional student.getCourse().get(0).setTitle("whatever"), those changes are also reflected in other students who share the same course. I need help with this, thank you
The student class
public class Student {
#Id
#SequenceGenerator(
name = "student_sequence",
sequenceName = "student_sequence",
allocationSize=1
)
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "student_sequence")
private Long studentId;
private String fullName;
#Column(name = "email_address", nullable = false)
private String email;
private String username;
private String password;
#ManyToMany(mappedBy = "students", fetch = FetchType.EAGER)
private List<Course> courses ;
public void addCourse(Course course) {
if (courses == null) {
courses = new ArrayList<>();
}
courses.add(course);
}
Course Class
public class Course {
#Id
#SequenceGenerator(
name = "course_sequence",
sequenceName = "course_sequence",
allocationSize = 1
)
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "course_sequence")
private Long courseId;
private String title;
private double courseRating = 0;
private LocalDateTime createdAt = LocalDateTime.now();
private double completedProgress = 0;
#Embedded
private CourseInformation courseInformation;
#OneToMany(cascade = CascadeType.MERGE, fetch = FetchType.EAGER)
#JoinColumn(name = "course_id", referencedColumnName = "courseId")
private List<CourseLecture> courseLectures;
#ManyToMany(
cascade = CascadeType.MERGE,
fetch = FetchType.LAZY
)
#JoinTable(
name = "student_course_mapping",
joinColumns = #JoinColumn(
name = "course_id",
referencedColumnName = "courseId"
),
inverseJoinColumns = #JoinColumn(
name = "student_id",
referencedColumnName = "studentId"
)
)
#ToString.Exclude
private List<Student> students;
There is no relationship mapping in the CourseLecture class.
This is not wrong, but just the way JPA works.
Technically it works, because they all reference the same instance as JPA guarantees to always return the same instance for a given class and id in single session.
If you don't want that you'd have to do the work either in different sessions, or you have to change your data model, so that each student has their own course. Of course this would be a strange model.
Update based on your comment:
Looks like indeed you need a different model, instead of Student -N-M-> Course you need something like Student -1-N-> Attendance -N-1-> Course, making the mapping table of your relationship into an entity and allowing it to store extra data that is specific to Student AND Course
I m new to Spring Boot. I have a table (Team) that has resources, am storing in a separate table (Resources) and have team_resource mapping table (with fields teamid, resourceid). My question is should I have a domain class for the mapping_table too ?
When I m inserting a new team (POST) with resources I create entry in all 3 tables. I m using facade/dao pattern for writing/ reading to the DB. I have to handle when the team is modified/ deleted. Should I have a domain class for the mapping_table?
There are multiple approaches you can handle it
Approach 1
Define #ManyToMany between your Team and Resources entity like this:
In Team Entity
#ManyToMany(fetch = FetchType.LAZY,
cascade = {
CascadeType.PERSIST,
CascadeType.MERGE
})
#JoinTable(name = "resources",
joinColumns = { #JoinColumn(name = "id") },
inverseJoinColumns = { #JoinColumn(name = "id") })
private Set<Resources> resources= new HashSet<>();
In your resources entity:
#ManyToMany(fetch = FetchType.LAZY,
cascade = {
CascadeType.PERSIST,
CascadeType.MERGE
},
mappedBy = "resources")
private Set<Team> teams= new HashSet<>();
Approach 2
#Entity
#Table(name = "team_resources")
public class TeamResources implements Serializable {
#EmbeddedId
private TeamResourcesId id;
#ManyToOne
#JoinColumn(name = "team_id", referencedColumnName = "id", insertable = false, updatable = false)
private Team team;
#ManyToOne
#JoinColumn(name = "resources_id", referencedColumnName = "id", insertable = false, updatable = false)
private Resources resources;
public TeamResources (Team u, Resources r) {
// create primary key
this.id = new TeamResourcesId (u.getUserId(), q.getQuestionId());
// initialize attributes
this.user = u;
this.question = q;
}
#Embeddable
public static class TeamResourcesId implements Serializable {
#Column(name = "team_id")
protected Long teamId;
#Column(name = "resources_id")
protected Long resourcesId;
public TeamResourcesId () {
}
public TeamResourcesId (Long teamId, Long resourcesId) {
this.teamId= teamId;
this.resourcesId= resourcesId;
}
//Getter , setter. equal and hash
}
so to answer your question, follow second approach and its good to not define bidirectional approach as it can lead to some run time problem if not handled properly.
How can inner join be done on Many to Many relations using Predicate BooleanExpression?
I have 2 entities
public class A {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;
#ManyToMany(fetch = FetchType.LAZY,
cascade = { CascadeType.DETACH, CascadeType.MERGE,
CascadeType.REFRESH, CascadeType.PERSIST})
#JoinTable(name = "a_b_maps",
joinColumns = #JoinColumn(name = "a_id", nullable =
false,referencedColumnName = "id"),
inverseJoinColumns = #JoinColumn(name = "b_id", nullable = false,
referencedColumnName = "id")
)
private Set<B> listOfB = new HashSet<B>();
}
public class B {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;
#ManyToMany(fetch = FetchType.LAZY,
cascade = { CascadeType.DETACH, CascadeType.MERGE,
CascadeType.REFRESH, CascadeType.PERSIST})
#JoinTable(name = "a_b_maps",
joinColumns = #JoinColumn(name = "b_id", nullable =
false,referencedColumnName = "id"),
inverseJoinColumns = #JoinColumn(name = "a_id", nullable = false,
referencedColumnName = "id")
)
private Set<A> listOfA = new HashSet<A>();
}
A Base repo
#NoRepositoryBean
public interface BaseRepository<E, I extends Serializable>
extends JpaRepository<E, I> {
}
And a repository class for A
public interface Arepo extends BaseRepository<A, Integer>,
QueryDslPredicateExecutor<A> {
Page<A> findAll(Predicate predicate, Pageable pageRequest);
}
Now I want to use A Repo with Predicate query. I need to form a predicate where I can load A based on some given Bs
I tried
QA a = QA.a;
QB b = QB.b;
BooleanExpression boolQuery = null;
JPQLQuery<A> query = new JPAQuery<A>();
query.from(a).innerJoin(a.listOfB, b)
.where(b.id.in(someList));
Now I am able to form a JPQLQuery, but the repository expects a Predicate. How can I get Predicate from the JPQLQuery??
Or, how can the inner join be achieved using Predicate?
I am able to create a Predicate with the help of answer given here
https://stackoverflow.com/a/23092294/1969412.
SO, instead of using JPQLQuery, I am directly using
a.listOfB.any()
.id.in(list);
This is working like a charm.