Question

以author，book和加入表author_books为例，加上royalty列：

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，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]
}

以下代码：

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，但由于author_books不能为空而无法插入royalty。

但是如果让db-reverse-engineer插件生成AuthorBooks类，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，我无法致电author.addToAuthorBooks(new AuthorBooks( ))，因为author_books无法author_id或book_id成为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，在作者和图书类中拥有hasMany关联有什么好处？有更好的方法吗？理想情况下，像下面这样的东西会很酷

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

Answer 1

我想推荐一些更改，特别是在您的AuthorBooks域中：

custom user control

为书籍和作者提供额外的ID是多余的。我不是100％肯定我会建议的，但是值得尝试以下内容：

custom user control

Grails：如何使用额外的列插入多对多？

1 个答案: