I have two entities, Books and Wishlist. My wish list contains books. I want to get the collection of books that are in my wish list ordered in the same order they were added to the wish list.
#ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
#JoinTable(name = "WISHLISTS_BOOKS", joinColumns = { #JoinColumn(name = "BOOK_ID") }, inverseJoinColumns = { #JoinColumn(name = "WISHLIST_ID") })
private Set<Book> books;
This is where I get stuck. There's an #OrderBy annotation but from what I understand it refers to a field in the book to use to order by. In my case, since a book can belong to multiple wish lists, I can't do that. Instead, I tried to create a added_ts timestamp field in the WISHLISTS_BOOKS join table but I'm not sure how to refer to it.
Can anyone help me sort this out?
You can use #OrderColumn(name = "added_ts") to achieve ordering.
#ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
#JoinTable(name = "WISHLISTS_BOOKS", joinColumns = { #JoinColumn(name = "BOOK_ID") }, inverseJoinColumns = { #JoinColumn(name = "WISHLIST_ID") })
#OrderColumn(name = "added_ts")
private Set<Book> books;
Related
#Entity
public class Post{
private Long id;
#ManyToMany(fetch = FetchType.LAZY)
#JoinTable(name = "tag_posts", joinColumns = #JoinColumn(name = "post_id", referencedColumnName = "id"), inverseJoinColumns = #JoinColumn(name = "post_id", referencedColumnName = "id"))
private Set<Tag> hashtags= new LinkedHashSet<>();
}
Hello I would like to sort hashtags by right order they got added in to post, is anything like this possible?
Or would I just change type to List? Wouldnt this affect performance?
Thanks.
I assume you want to retrieve Post along with the tags but you want tags in the order it got added to the Post.
You can use #OrderBy annotation to get the list of tags while retrieving.
#Entity
public class Post{
private Long id;
#OrderBy(value="orderField")
#ManyToMany(fetch = FetchType.LAZY)
#JoinTable(name = "tag_posts", joinColumns = #JoinColumn(name = "post_id", referencedColumnName = "id"), inverseJoinColumns = #JoinColumn(name = "post_id", referencedColumnName = "id"))
private Set<Tag> hashtags= new LinkedHashSet<>();
}
If you want to create a column in the join table which will keep the same order you can use #OrderByColumn("orderField")
I have three tables. tbl_vendor and tbl_category tables are mapped using #ManyToMany relation. When I am getting 'Vendors' under a particular 'Category' I am also getting 'Areas' because tbl_vendor and tbl_area are also mapped using #ManyToMany.
relations:
in tbl_vendor Model :
#ManyToMany(cascade = CascadeType.DETACH, fetch = FetchType.LAZY)
#JoinTable(name = "tbl_category_vendor", joinColumns = {#JoinColumn(name = "vendor_id")}, inverseJoinColumns = {#JoinColumn(name = "category_id")})
private Set<Category> categories = new HashSet<>();
....
#ManyToMany(cascade = CascadeType.DETACH, fetch = FetchType.LAZY)
#JoinTable(name = "tbl_area_vendor", joinColumns = {#JoinColumn(name = "vendor_id")}, inverseJoinColumns = {#JoinColumn(name = "area_id")})
private Set<Area> areas = new HashSet<>();
in tbl_category Model :
#JsonIgnore
#ManyToMany(cascade = CascadeType.DETACH, mappedBy = "categories", fetch = FetchType.LAZY)
private List<Vendor> vendors = new ArrayList<>();
in tbl_area Model :
#JsonIgnore
#ManyToMany(mappedBy = "areas", fetch = FetchType.LAZY)
private List<Vendor> vendors = new ArrayList<>();
I have a particular case where I don't need this 'Area' with 'Vendor'.
is there any way to ignore already mapped 'Area' from 'Vendor' using JpaRepository in some particular case ?
I never do this, but someone on my project created a many to many relationship between, let's say, a Foo and a Bar. Foo and Bar both have unique system generated IDs. On Foo, I have the following code:
#ManyToMany(targetEntity = Bar.class, cascade = CascadeType.ALL, fetch = FetchType.EAGER)
#JoinTable(name = "FOO_BAR_LNK",
joinColumns = {#JoinColumn(name = "FOO_ID", referencedColumnName = "ID")},
inverseJoinColumns = {#JoinColumn(name = "BAR_ID", referencedColumnName = "ID")})
private Set<Bar> bars;
When the table gets created, it has 3 columns, HIBERNATE_IDX, FOO_ID and BAR_ID. HIBERNATE_IDX contains all zeroes.
What is HIBERNATE_IDX?
It appears that HIBERNATE_IDX is part of a tie-breaker to guarantee unique indices on join tables and prevent cartesian products. Kind of pieced together, but that's what I think.
I have quite big problem with hibernate annotation mapping. Heres my diagram:
As for mapping object, few are simple cause its 1...N for:
TASK_DEF -> REPORT_DATA
REPORT_DATA -> REPORT_DATA_COLUMN
REPORT_DATA -> REPORT_DATA_VALUE
right?
Now problem is when I'm trying to map Collection of REPORT_DATA_VALUE to REPORT_DATA_COLUMN. I've tried this way:
#OneToMany(fetch = FetchType.LAZY)
#ForeignKey(name = "FK_REPORT_DATA_VALUE_REPORT_DA", inverseName = "PK_REPORT_DATA_COLUMN")
#JoinTable(name = "REPORT_DATA_VALUE", joinColumns = {
#JoinColumn(name = "REPORT_DATA_ID"),
#JoinColumn(name = "COLUMN_NM")
}, inverseJoinColumns = {
#JoinColumn(name = "REPORT_DATA_ID"),
#JoinColumn(name = "COLUMN_NM")
})
List<ReportDataValue> reportDataValueList;
But hibernate selects wrong identifies, therefore couldnt execute query. Could someone help me with this?
There is a problem in your code. Try this instead:
#OneToMany(fetch = FetchType.LAZY)
#JoinTable(name = "REPORT_DATA_VALUE", joinColumns = {
#JoinColumn(name = "REPORT_DATA_ID"),
}, inverseJoinColumns = {
#JoinColumn(name = "COLUMN_NM")
})
List<ReportDataValue> reportDataValueList;
By the way, If I were you, I wouldn't create a table for One To Many. I'd do this:
public class A{
#ManyToOne(fetch=FetchType.LAZY)
#JoinColumn(name="B_ID")
B b;
}
public class B{
#OneToMany(mappedBy="b",fetch=FetchType.EAGER)
Set<A> as;
}
Let I have Tables (Books and Authors have ManyToMany relation ship)
BOOKS
id
book_name
AUTHORS
id
author_name
BOOKS_AUTHORS
id
book_id
author_id
I map this Tables on Entities
class Books
{
#Id
long id;
#Column(name = "author_name")
String name;
#ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
#JoinTable(name = "BOOKS_AUTHORS",
joinColumns = #JoinColumn(name = "book_id"),
inverseJoinColumns = #JoinColumn(name = "author_id"))
List<Authots> authors;
// setter, getters, adder
}
class Authors
{
#Id
long id;
#Column(name = "author_name")
String name;
#ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
#JoinTable(name = "BOOKS_AUTHORS",
joinColumns = #JoinColumn(name = "author_id"),
inverseJoinColumns = #JoinColumn(name = "book_id"))
List<Books> books;
// setter, getters, adder
}
Now, I try do next
public void addAuthor(final String bookName, final Author author)
{
final Book book = // get book from database by bookName
if (book == null)
throw new DataNotFoundException("Book not found :(");
author.addBook(book);
book.addAuthor(author);
entityManager.persist(author);
}
1) I get exception that ID of BOOKS_AUTHORS record must be not NULL
2) How I can Generate ID (ising sequance generator) for relationship-table BOOKS_AUTHORS
You cannot use #ManyToMany to create join table with id field in it.
If id field in the join table is a requirement, you have to create a special entity class (such as BookAuthor) for that table and connect it with books and authors with #ManyToOne/#OneToMany relationships.
Otherwise you need to remove id field from BOOKS_AUTHORS table.
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
private long id;
If books_authors is not mapped using Hibernate, then use the database side auto id incrementor. Example:
ALTER table book_authors CHANGE id long NOT NULL AUTO_INCREMENT;
Try using Projection
session.CreateCriteria(typeof (BOOKS_AUTHORS))
.SetProjection(Projections.Max("Id"))
.UniqueResult()
and add to it +1 :) Sory its .net code im not familiar with java hope it will help you.
In SpringBoot 1.5.3 and spring-boot-starter-data-jpa you can use annotation {#OrderColumn(name = "id")}. For you example it should looks like:
#ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
#JoinTable(name = "BOOKS_AUTHORS",
joinColumns = #JoinColumn(name = "author_id"),
inverseJoinColumns = #JoinColumn(name = "book_id"))
#OrderColumn(name = "id")
List<Books> books;