grails - Grails:如何使用多列插入多对多？

Question

以author，book和带有额外的author_books列的联接表royalty为例:

CREATE TABLE 'author_books' (
    'author_id` bigint(20) NOT NULL,
    'book_id' bigint(20) NOT NULL,
    'royalty' int NOT NULL,
    PRIMARY KEY ('author_id', 'book_id') ,
    INDEX 'FK24C812F6183CFE1B' ('book_id'),
    INDEX 'FK24C812F6DAE0A69B' ('author_id')

)

如果我没有db-reverse-engineer插件生成AuthorBooks类，则生成的代码将是:

class Author {
    String name
    static hasMany = [books: Book]
}

class Book {
    String title
    static hasMany = [authors: Author]
    static belongsTo = [Author]
}

如下代码:

def author1 = new Author(name: 'author1').addToBooks(new Book(title: 
                         'book1')).save(flush: true)

会在 author表中插入一行，在 book表中插入一行，但是由于 author_books不能为null，因此无法插入到 royalty中。

但是，如果让db-reverse-engineer插件生成AuthorBooks类，则生成的代码将是:

class Author {
    String name
    static hasMany = [authorBookses: AuthorBooks]
}

class Book {
    String title
    static hasMany = [authorBookses: AuthorBooks]
}

class AuthorBooks implements Serializable {
    Long authorId
    Long bookId
    Integer royalty
    Author author
    Book book

    int hashCode() {
        def builder = new HashCodeBuilder()
        builder.append authorId
        builder.append bookId
        builder.toHashCode()
    }

    boolean equals(other) {
        if (other == null) return false
        def builder = new EqualsBuilder()
        builder.append authorId, other.authorId
        builder.append bookId, other.bookId
        builder.isEquals()
    }

    static belongsTo = [author: Author, book: Book]

    static mapping = {
        author insertable: false       // these insertable and updateable codes were manually added
        author updateable: false       // otherwise it would not run
        book insertable: false
        book updateable: false
        id composite: ["authorId", "bookId"]
        version false
   }
}

在这种情况下，我无法调用 author.addToAuthorBooks(new AuthorBooks( ))，因为 author_books不能将 author_id或 book_id设置为 null。最后，我需要执行以下操作才能使其正常工作:

def author1 = new Author(name: 'author1').save(flush: true)
def book1 = new Book(title: 'book1').save(flush: true)
def authorbook1 = new AuthorBooks(authorId: author1.id, bookId: book1.id, 
                      royalty: 50, author: author1, book: book1).save(flush: true)

这是我可以接受的。但是在Author和Book类中拥有hasMany关联有什么好处呢？还有更好的方法吗？理想情况下，跟随以下操作会很酷

def author1 = new Author(name: 'author1').addToBooks(book: new Book(title: 'book1'), 
                         royalty: 50).save(flush: true)

Answer 1

我建议您进行一些更改，特别是在您的AuthorBooks域中:

class Author {
    String name
    static hasMany = [authorBookses: AuthorBooks]
}

class Book {
    String title
    static hasMany = [authorBookses: AuthorBooks]
}

class AuthorBooks implements Serializable {
    Integer royalty
    Author author
    Book book

    int hashCode() {
        def builder = new HashCodeBuilder()
        builder.append author.id
        builder.append book.id
        builder.toHashCode()
    }

    boolean equals(other) {
        if (other == null) return false
        def builder = new EqualsBuilder()
        builder.append author.id, other.author.id
        builder.append book.id, other.book.id
        builder.isEquals()
    }

    static belongsTo = [author: Author, book: Book]

    static mapping = {
        id composite: ["author", "book"]
        version false
   }
}

为书籍和作者添加其他ID是多余的。我不确定要提出的建议，但值得尝试以下方法:

def author1 = new Author(name: 'author1', authorBookses: new HashSet())
def book1 = new Book(title: 'book1', authorBookses: new HashSet())
def authorbook1 = new AuthorBooks(royalty: 50, author: author1, book: book1)

author1.authorBookses(authorbook1)
book1.authorBookses(authorbook1)

authorbook1.save(flush: true)