Question

想象一下以下关系

一本书由许多章组成，一章只属于一本书。经典的一对多关系。

我将其建模为：

case class Book(id: Option[Long] = None, order: Long, val title: String)

class Books(tag: Tag) extends Table[Book](tag, "books")
{
  def id = column[Option[Long]]("id", O.PrimaryKey, O.AutoInc)
  def order = column[Long]("order")
  def title = column[String]("title")

  def * = (id, order, title) <> (Book.tupled, Book.unapply)
  def uniqueOrder = index("order", order, unique = true)

  def chapters: Query[Chapters, Chapter, Seq] = Chapters.all.filter(_.bookID === id)
}

object Books
{
  lazy val all = TableQuery[Books]
  val findById = Compiled {id: Rep[Long] => all.filter(_.id === id)}

  def add(order: Long, title: String) = all += new Book(None, order, title)
  def delete(id: Long) = all.filter(_.id === id).delete

//  def withChapters(q: Query[Books, Book, Seq]) = q.join(Chapters.all).on(_.id === _.bookID)

  val withChapters = for
  {
    (Books, Chapters) <- all join Chapters.all on (_.id === _.bookID)
  } yield(Books, Chapters)
}

case class Chapter(id: Option[Long] = None, bookID: Long, order: Long, val title: String)

class Chapters(tag: Tag) extends Table[Chapter](tag, "chapters")
{
  def id = column[Option[Long]]("id", O.PrimaryKey, O.AutoInc)
  def bookID = column[Long]("book_id")
  def order = column[Long]("order")
  def title = column[String]("title")

  def * = (id, bookID, order, title) <> (Chapter.tupled, Chapter.unapply)
  def uniqueOrder = index("order", order, unique = true)

  def bookFK = foreignKey("book_fk", bookID, Books.all)(_.id.get, onUpdate = ForeignKeyAction.Cascade, onDelete = ForeignKeyAction.Restrict)
}

object Chapters
{
  lazy val all = TableQuery[Chapters]
  val findById = Compiled {id: Rep[Long] => all.filter(_.id === id)}

  def add(bookId: Long, order: Long, title: String) = all += new Chapter(None, bookId, order, title)
  def delete(id: Long) = all.filter(_.id === id).delete
}

现在我想做什么：

我想查询所有或特定图书（按ID）及其所有章节

转换为纯SQL，类似于：

SELECT * FROM books b JOIN chapters c ON books.id == c.book_id WHERE books.id = 10

但是在Slick中我无法真正完成这一切。

我尝试了什么：

object Books
{
    //...
    def withChapters(q: Query[Books, Book, Seq]) = q.join(Chapters.all).on(_.id === _.bookID)
}

以及：

object Books
{
    //...
    val withChapters = for
    {
        (Books, Chapters) <- all join Chapters.all on (_.id === _.bookID)
    } yield(Books, Chapters)
}

但无济于事。（我使用ScalaTest，我得到一个空结果（def withChapters(...)）或val withChapters = for...的另一个例外）

如何继续这个？我试图保留文档，但显然我做错了。

另外：有没有一种简单的方法可以将实际查询视为字符串？我只找到query.selectStatement之类的内容，但这不适用于我加入的查询。非常适合调试以查看实际查询是否错误。

编辑：我的测试如下：

class BookWithChapters extends FlatSpec with Matchers with ScalaFutures with BeforeAndAfter
{
  val db = Database.forConfig("db.test.h2")

  private val books = Books.all
  private val chapters = Chapters.all

  before { db.run(setup) }
  after {db.run(tearDown)}

  val setup = DBIO.seq(
    (books.schema).create,
    (chapters.schema).create
  )

  val tearDown = DBIO.seq(
    (books.schema).drop,
    (chapters.schema).drop
  )

  "Books" should "consist of chapters" in
  {
    db.run(
      DBIO.seq
      (
        Books.add(0, "Book #1"),
        Chapters.add(0, 0, "Chapter #1")
      )
    )

    //whenReady(db.run(Books.withChapters(books).result)) {
    whenReady(db.run(Books.withChapters(1).result)) {
    result => {
      //  result should have length 1
        print(result(0)._1)
      }
    }
  }
}

像这样我得到IndexOutOfBoundsException。

我用这个作为我的方法：

object Books
{
      def withChapters(id: Long) = Books.all.filter(_.id === id) join Chapters.all on (_.id === _.bookID)
}

也：

logback.xml看起来像这样：

<configuration>
    <logger name="slick.jdbc.JdbcBackend.statement" level="DEBUG/>
</configuration>

我在哪里可以看到日志？或者我还需要做些什么才能看到它们？

Answer 1

翻译您的查询...

SELECT * FROM books b JOIN chapters c ON books.id == c.book_id WHERE books.id = 10

...要点赞，我们可以filter books：

val bookTenChapters = 
  Books.all.filter(_.id === 10L) join Chapters.all on (_.id === _.bookID)

这将为您提供一个返回Seq[(Books, Chapters)]的查询。如果要选择不同的书籍，可以使用不同的过滤表达式。

或者，您可能希望过滤联接：

val everything = 
   Books.all join Chapters.all on (_.id === _.bookID)

val bookTenChapters = 
  everything.filter { case (book, chapter) => book.id === 10L }

这可能会更接近您的加入。检查使用您使用的数据库生成的SQL，看看您喜欢哪个。

您可以通过创建src/main/resources/logback.xml文件并设置：

来记录查询

 <logger name="slick.jdbc.JdbcBackend.statement" level="DEBUG"/>

我有example project with logging set up。您需要在xml文件中将INFO更改为DEBUG，例如，在章01文件夹中。

Slick 3加入查询一对多关系

1 个答案: