如何检索与电梯的多对多关系数据

Question

让我说我有3个表：书，作者和BookAuthor。

Book has id, title 
Author has id, name 
BookAuthor has id, book_id, author_id 

我想查找一本书的所有作者。任何人都可以指导我如何用Lifts mapper语法来做到这一点？

Answer 1

下面是书中的映射：

class Book extends LongKeyedMapper[Book] with IdPk with OneToMany[Long, Book] { 
    def getSingleton = Book 
    object title extends MappedString(this, 200) 
    object BookAuthor extends MappedOneToMany(BookAuthor, BookAuthor.id) 
} 
object Book extends Book with LongKeyedMetaMapper[Book] 

的特质IdPk将书的ID的照顾。那么对于BOOKAUTHOR：

class BookAuthor extends LongKeyedMapper[BookAuthor] with IdPk with OneToOne[Long, BookAuthor] { 
    def getSingleton = BookAuthor 
    object Author extends MappedOneToOne(Author, Author.id) 
} 
object BookAuthor extends BookAuthor with LongKeyedMetaMapper[BookAuthor] 

然后作者，一个简单的映射：

class Author extends LongKeyedMapper[Author] with IdPk { 
    def getSingleton = Author 
    object name extends MappedString(this, 200) 
} 
object Author extends Author with LongKeyedMetaMapper[Author] 

然后打电话找一本书（这里myBook）的所有作者：

myBook.BookAuthor.map(x => x.Author.name) 

如果您想要进行更复杂的加入请求而不必过滤Scala中的所有内容，您始终可以使用DB，并且您始终可以找到有关映射器的更多信息here 。

Answer 2

class Book extends LongKeyedMapper[Book] 
           with IdPK 
           with ManyToMany { 
    def getSingleton = Book 
    object title extends MappedString(this, 255) 
    object authors extends MappedManyToMany( 
     BookAuthors, BookAuthors.book, BookAuthors.author, Author) 
} 

object Book extends Book with LongKeyedMetaMapper[Book] 

class Author extends LongKeyedMapper[Author] 
           with CreatedUpdated with IdPK 
           with ManyToMany { 
    def getSingleton = Author 
    object firstName extends MappedString(this, 255) 
    object lastName extends MappedText(this) 
    object email extends MappedEmail(this, 150) 
    object books extends MappedManyToMany(BookAuthors, 
      BookAuthors.author,  BookAuthors.book, Book) 

} 

object Author extends Author with LongKeyedMetaMapper[Author] 

val warandpeace = Book.create.title("War and Peace").saveMe 
val fred = Author.create.firstName("Fred").saveMe 
fred.books += warandpeace 
fred.saveMe 
val bob = Author.create.firstName("Bob").saveMe 
bob.books += warandpeace 
bob.saveMe 

// then to find all the authors of the book: 
val authors = warandpeace.authors