[英]Slick 3 join query one to many relationship
想象以下關系
一本書由許多章組成,一章恰好屬於一本書。 經典的一對多關系。
我將其建模為:
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
}
現在我要做的是:
我想查詢所有或特定書籍(按ID) 及其所有章節
轉換為普通SQL,類似:
SELECT * FROM books b JOIN chapters c ON books.id == c.book_id WHERE books.id = 10
但是在Slick中,我無法真正完成整個工作。
我試過的
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)
}
但無濟於事。 (我使用ScalaTest並得到一個空結果(對於def withChapters(...)
)或val withChapters = for...
另一個異常)
怎么繼續呢? 我試圖保留文檔,但是顯然我做錯了。
另外:有沒有一種簡單的方法可以將實際查詢視為字符串? 我只找到了query.selectStatement
之類的東西,但不適用於我加入的查詢。 對於調試以查看實際查詢是否錯誤將非常有用。
編輯:我的測試如下所示:
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)
}
}
}
}
這樣,我得到一個IndexOutOfBoundsException
。
我用它作為我的方法:
object Books
{
def withChapters(id: Long) = Books.all.filter(_.id === id) join Chapters.all on (_.id === _.bookID)
}
也:
logback.xml
看起來像這樣:
<configuration>
<logger name="slick.jdbc.JdbcBackend.statement" level="DEBUG/>
</configuration>
我在哪里可以看到日志? 或者我還必須做什么才能看到它們?
要翻譯您的查詢...
SELECT * FROM books b JOIN chapters c ON books.id == c.book_id WHERE books.id = 10
...對於Slick,我們可以filter
books
:
val bookTenChapters =
Books.all.filter(_.id === 10L) join Chapters.all on (_.id === _.bookID)
這將為您提供一個返回Seq[(Books, Chapters)]
。 如果要選擇其他書籍,則可以使用其他過濾器表達式。
或者,您可能希望過濾聯接:
val everything =
Books.all join Chapters.all on (_.id === _.bookID)
val bookTenChapters =
everything.filter { case (book, chapter) => book.id === 10L }
那可能更接近您的加入。 檢查使用您的數據庫生成的SQL,以查看您喜歡的數據庫。
您可以通過創建src/main/resources/logback.xml
文件並設置以下內容來記錄查詢:
<logger name="slick.jdbc.JdbcBackend.statement" level="DEBUG"/>
我有一個建立日志記錄的示例項目 。 您將需要將xml文件(例如,Chapter-01文件夾)中的INFO
更改為DEBUG
。
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