I have 2 entities Board and Tag. They have a many to many relationship joined by the table board_tag_table. When I add the tags to the board, it saves the correct pair id to the join table. However when I try to output the Board using Thymeleaf my tags show up as blank.
#Table(name="board_table")
public class Board {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
private String title;
#ManyToMany(fetch = FetchType.LAZY,cascade = CascadeType.ALL)
#JoinTable(name = "board_tag_table",
joinColumns = {
//primary key of Board
#JoinColumn(name = "id", referencedColumnName = "id")
},
inverseJoinColumns = {
//primary key of Tag
#JoinColumn(name = "tag_id", referencedColumnName = "tag_id")
})
private Set<Tag> tags = new HashSet<>();
}
#Table(name="tag_table")
public class Tag {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer tag_id;
private String tagname;
#JsonIgnore
#ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "tags")
private Set<Board> boards = new HashSet<>();
}
<tr th:each="board : ${list}">
<td th:text="${board.id}"></td>
<td>
<a th:text="${board.title}" th:href="#{/board/view(id=${board.id})}"></a>
</td>
<td th:text="${board.tags}"> </td>
I tried creating a seperate repository and entity for the join table but keep getting an error.
Related
I have a ManyToMany relationship that is broken down into 2 OneToMany relation. A Book can belong to multiple Categories and a Category can have many Books.
When I query for Book, the categories list just get empty. How can I get a list of all Categories that a Book belong to ? Am I missing something ?
#Entity
public class Book {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;
#NotBlank(message = "Please input book title")
private String title;
private Integer publishYear;
private String publisher;
private String language;
private Integer numberOfPages;
private String avatarUrl;
#OneToMany(targetEntity = BookCategory.class, cascade = CascadeType.ALL)
#JoinColumn(name = "category", nullable = false, insertable = false, updatable = false)
private Set<BookCategory> categories = new LinkedHashSet<>();
}
#Entity
public class Category {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;
#Column(nullable = false)
#NotBlank(message = "Please input category name")
private String name;
}
#Entity
public class BookCategory {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;
#ManyToOne
#JoinColumn(name = "book", nullable = false)
private Book book;
#ManyToOne
#JoinColumn(name = "category", nullable = false)
private Category category;
}
Try using mappedBy attribute with #OneTOMany annotation on the 'One' side of the OneToMany relation.
Or you can also try using the following:
#ManyToMany
#JoinTable(
name = “book”_category,
joinColumns = #JoinColumn(name = “book_id”),
inverseJoinColumns = #JoinColumn(name = “category_id))
Read more:
https://vladmihalcea.com/the-best-way-to-use-the-manytomany-annotation-with-jpa-and-hibernate/
I have two tables that have a manytomany relationship:
first one is ad ( represents all the products)
#Entity
#Table(name = "ad")
public class Ad {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
#ManyToOne(cascade = CascadeType.PERSIST)
#JoinColumn(name = "admin_id")
private Admin admin;
#ManyToMany(mappedBy = "ads", fetch = FetchType.LAZY)
private List<Order> orders = new ArrayList<>();
Second one is order:
#Entity
#Table(name = "`order`")
public class Order {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
#ManyToOne( cascade=CascadeType.
#JoinColumn(name = "buyer_id")
private Buyer buyer;
#ManyToMany(fetch = FetchType.LAZY)
#JoinTable(name = "order_ad", joinColumns = {
#JoinColumn(name = "order_id", referencedColumnName = "id", nullable = false, updatable = false) }, inverseJoinColumns = {
#JoinColumn(name = "ad_id", referencedColumnName = "id", nullable = false, updatable = false) })
private List<Ad> ads = new ArrayList<>();
when I delete order using its repository that is representing a cancellation so I don't want the ads to be deleted as well.
How can I do that?
PS: I can't find a replacement for the orphanRemoval of the onetomany relationship
I have a class called Tag:
#Entity
#Table(name = "tags")
public class Tag {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
#ManyToMany(fetch = FetchType.LAZY,
cascade = {
CascadeType.PERSIST,
CascadeType.MERGE
},
mappedBy = "tags")
private Set<Post> posts = new HashSet<>();
...
}
And a class called Post
#Entity
#Table(name = "posts")
public class Post {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#ManyToMany(fetch = FetchType.LAZY,
cascade = {
CascadeType.PERSIST,
CascadeType.MERGE
})
#JoinTable(name = "post_tags",
joinColumns = { #JoinColumn(name = "post_id") },
inverseJoinColumns = { #JoinColumn(name = "tag_id") })
private Set<Tag> tags = new HashSet<>();
...
}
It creates another table named post_tags.
How can I write a Controller to access that table as it is not similar a repository?
Is there more easy and convenient way to implement ManyToMany relationship ?
My pom.xml
You don't need to access that relation table manually. You can load load all Tag entities, and then load all the referenced Post entities.
The relation table is enterily managed by your ORM frameork.
But, if you still want to access the relation table, you can use native queries in your Spring Data JPA repository, e.g.
#Query(value="select post_id, tag_id from post_tags", nativeQuery=true)
List<PostTag> loadPostTags();
PostTag class is not a jpa-managed entity and must match the structue of the returned table:
public class PostTag {
private long postId;
private long tagId;
// getter, setter
}
Use this way
#Entity
#Table(name = "tags")
public class Tag {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
#ManyToMany(cascade = CascadeType.ALL)
#JoinTable(name = "post_tags",
joinColumns = { #JoinColumn(name = "id") },
inverseJoinColumns = { #JoinColumn(name = "post_id") })
private Set<Post> posts = new HashSet<>();
...
}
#Entity
#Table(name = "posts")
public class Post {
#Id
#Column(name = "post_id")
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long postId;
...
}
here job has a set of employees, and employee have a set of jobs, but Spring give me this exception
Caused by: org.hibernate.MappingException: Foreign key
(FK1kec5bwba2rl0j8garlarwe3d:account [employee_id])) must have same
number of columns as the referenced primary key (employee
[job_id,employee_id])
this is my employee class :
#Entity
public class Employee {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Integer id ;
private String firstname ;
private String lastname ;
private String email ;
private String phone ;
private String address ;
#OneToOne(cascade = CascadeType.ALL)
#JoinColumn(name = "account_id")
private Account account ;
public Account getAccount() {
return account;
}
public void setAccount(Account account) {
this.account = account;
}
#ManyToOne
#JoinColumn(name = "departement_id")
#JsonIgnore
private Departement departement ;
#ManyToMany(cascade = CascadeType.ALL)
#JoinTable(name = "jobs", joinColumns = #JoinColumn(name = "employee_id", referencedColumnName = "id"), inverseJoinColumns = #JoinColumn(name = "job_id", referencedColumnName = "id"))
private Set<Job>jobs ;
....
}
and here is my job class :
#Entity
#Inheritance
public abstract class Job {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Integer id ;
private String status ; // (pending or done)
private Date date ;
#ManyToMany(cascade = CascadeType.ALL)
#JoinTable(name = "employee", joinColumns = #JoinColumn(name = "job_id", referencedColumnName = "id"), inverseJoinColumns = #JoinColumn(name = "employee_id", referencedColumnName = "id"))
private Set<Employee> employee ;
#ManyToOne
#JoinColumn(name = "BusinnesPartner_id")
#JsonIgnore
private BusineesPartner busineesPartner ;
}
Please can you explain to me why I get this exception.
#JoinTable annotation should be used in the owning entity side , in the other side you should not have #JoinTable , you need to have mappedBy to define the reverse relation since you are establishing a bidirectional relation is if the Job is the owning entity you need to modify Employee pojo
#ManyToMany(cascade = CascadeType.ALL, mappedBy="employee")
private Set<Job>jobs ;
I have two entities which are in many to many relation and I can't load Set <Category> categories. These fields are filled in the database.
#Entity
#Table(name="Product")
public class Product {
#Id
#GeneratedValue
private int idProduct;
private String status;
private String name;
#ManyToMany(fetch = FetchType.EAGER, mappedBy= "products")
private Set <Category> categories;
}
#Entity
#Table(name="Category")
public class Category {
#Id
#GeneratedValue
private int idCategory;
private String name;
#ManyToMany(fetch = FetchType.EAGER)
private Set <Product> products;
}
This returns nothing int the view and the loop doesn't rotate even once.
<c:forEach items="${product.categories}" var="items">
<p>${items.name}</p>
</c:forEach>
I join the schema. Could someone write what to do to make it work, please?
enter image description here
This not works.
#Entity
#Table(name="Category")
public class Category {
#Id
#GeneratedValue
private int idCategory;
private String name;
#ManyToMany(fetch = FetchType.EAGER)
#JoinTable(name = "Product_Category", joinColumns = {
#JoinColumn(name = "Category_idCategory", nullable = false, updatable = false) },
inverseJoinColumns = { #JoinColumn(name = "Product_idProduct",
nullable = false, updatable = false) })
private Set <Product> product;
Hibernate infers the sql that it needs to create from the annotation on the objects. Your product entity is telling hibernate to get information about the SQL join from the Category entity. This is from the mappedBy clause in the #ManyToMany annotation.
When it goes to the Category entity, it doesn't find what it needs, and it just gives an empty set.
Most #ManyToMany annotations are done with a join table. Here is a sample join table annotation
#JoinTable(name = "product_to_category", joinColumns = {
#JoinColumn(name = "category_id", nullable = false, updatable = false) },
inverseJoinColumns = { #JoinColumn(name = "product_id",
nullable = false, updatable = false) })
Depending on your schema, you might need to adjust the above annotation to get it working. It will give you a good start.