JPA持续存在ManyToMany错误未选择数据库

Question

I have 2 tables. Book and Category . A book can have multiple categories, and a category can have a list of book, right? So I create a new table category_book to make a ManyToMany relationship, with only book_id(fk) and category_id(fk) in it.

My Book Entity:

 @Id
@Column(name = "book_id", nullable = false)
@GeneratedValue(strategy=GenerationType.SEQUENCE)
private int bookId;

@ManyToMany
@JoinTable(name = "category_book", joinColumns = @JoinColumn(name = "book_id"), inverseJoinColumns = @JoinColumn(name = "category_id"))
private List<CategoryEntity> categoriesList;

...other basic attributes and constructors and getters and setters.....

My Category Entity:

@Id
@Column(name = "category_id", nullable = false)
@GeneratedValue(strategy=GenerationType.SEQUENCE)
private int categoryId;

@ManyToMany(mappedBy = "categoriesList", cascade = CascadeType.PERSIST)
private List<BookEntity> bookEntityList;

The servlet to add new book (categories already added seperately before.)

String[] category= request.getParameterValues("checkbox_category");
List<CategoryEntity> categoryEntityList = new ArrayList<>();
BookEntity newbook = new BookEntity();


for(String s: category){
       CategoryEntity categoryEntity2 = new CategoryEntity();
                categoryEntity2.setCategoryId(Integer.parseInt(s));   
       categoryEntityList.add(categoryEntity);
            }
    newbook.setCategories(categoryEntityList);
bookSessionBean.addBook(newbook);

BookSessionBean:

public void addBook(BookEntity book){
    em.persist(book);
}

I checked many topics, but couldn't solve the problem. The error keeps showing.

Internal Exception: java.sql.SQLException: No database selected
Error Code: 1046
Call: INSERT INTO category_book (category_id, book_id) VALUES (?, ?)
    bind => [2 parameters bound]
Query: DataModifyQuery(name="categoriesList" sql="INSERT INTO category_book (category_id, book_id) VALUES (?, ?)")

or

    Error Code: 1046
Call: ALTER TABLE category_book ADD CONSTRAINT FK_category_book_category_id FOREIGN KEY (category_id) REFERENCES book.category (category_id)
Query: DataModifyQuery(sql="ALTER TABLE category_book ADD CONSTRAINT FK_category_book_category_id FOREIGN KEY (category_id) REFERENCES book.category (category_id)")

All other things can persist successfully, only this ManyToMany cause troubles.

UPDATE: It's not because of connection URL jdbc, I'm using connection pool to get database and it's correct. If I remove the all the @ManyToMany relationship related, it will run normal. But this time I need to use ManyToMany relationship.

The persistence.xml file:

    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
    <jta-data-source>jdbc/book</jta-data-source>  
    <properties>
        <property name="javax.persistence.schema-generation.database.action" value="create"/>
    </properties>

UPDATE 2: I just check clearly, I tried to remove all ManyToMany related, it's working perfectly, but since I add @ManyToMany back again, it gives many errors, even it's still deploys successfully (but can't add new book or add to new table category_book via servlet and service session bean )

Still haven't find anything to solve this problem. Am I doing anything wrong?

Answer 1

Well, this can only mean you haven't configured the persistance.xml correctly.

The way the connection url should look like is:

"jdbc:databaseType://ip:port/databaseName"

example: "jdbc:mysql://localhost:3306/books"

Answer 2

So, after of hours and hours researching on the internet what's the problem, but no help. Then at some point I tried to look into the error message, and the problem is the one I find it hard to understand, no other place ever mentions it.

The error No Database Selected is because of the name column in the @ManyToMany @JoinTable annotation. I need to put the databasename.columnname then it's working. But I check many many tutorials and some answers/questions here, they dont need databasename , weird, right? And If I use @Column I dont need databasename at all.

@Id
@Column(name = "book_id", nullable = false)
@GeneratedValue(strategy=GenerationType.SEQUENCE)
private String bookId

    @ManyToMany(cascade = CascadeType.MERGE)
@JoinTable(name = "book.category_book", joinColumns = @JoinColumn(name = "book_id"), inverseJoinColumns = @JoinColumn(name = "category_id"))
//The correct one. `book` is my databasename. 

To get the code working more correctly, because in table category_book I have 2 primary keys book_id and category_id (works as foreign key), I have to change the ArrayList to HashSet to allow duplicated keys.

private Set<CategoryEntity> categoriesList = new HashSet<>();

I remove casdade for CategoryEntity, add cascade MERGE for BookEntity.

Now everything's working and running.