如何檢索與電梯的多對多關係數據

Question

讓我說我有3個表：書，作者和BookAuthor。

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

我想查找一本書的所有作者。任何人都可以指導我如何用Lifts mapper語法來做到這一點？

Answer 1

下面是書中的映射：

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] 

的特質IdPk將書的ID的照顧。那麼對於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] 

然後作者，一個簡單的映射：

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

然後打電話找一本書（這裏myBook）的所有作者：

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

如果您想要進行更復雜的加入請求而不必過濾Scala中的所有內容，您始終可以使用DB，並且您始終可以找到有關映射器的更多信息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