[英]Slick 3 join query one to many relationship
想象以下关系
一本书由许多章组成,一章恰好属于一本书。 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
}
现在我要做的是:
我想查询所有或特定书籍(按ID) 及其所有章节
转换为普通SQL,类似:
SELECT * FROM books b JOIN chapters c ON books.id == c.book_id WHERE books.id = 10
但是在Slick中,我无法真正完成整个工作。
我试过的
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)
}
但无济于事。 (我使用ScalaTest并得到一个空结果(对于def withChapters(...)
)或val withChapters = for...
另一个异常)
怎么继续呢? 我试图保留文档,但是显然我做错了。
另外:有没有一种简单的方法可以将实际查询视为字符串? 我只找到了query.selectStatement
之类的东西,但不适用于我加入的查询。 对于调试以查看实际查询是否错误将非常有用。
编辑:我的测试如下所示:
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)
}
}
}
}
这样,我得到一个IndexOutOfBoundsException
。
我用它作为我的方法:
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? 或者我还必须做什么才能看到它们?
要翻译您的查询...
SELECT * FROM books b JOIN chapters c ON books.id == c.book_id WHERE books.id = 10
...对于Slick,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)]
。 如果要选择其他书籍,则可以使用其他过滤器表达式。
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 }
那可能更接近您的加入。 检查使用您的数据库生成的SQL,以查看您喜欢的数据库。
您可以通过创建src/main/resources/logback.xml
文件并设置以下内容来记录查询:
<logger name="slick.jdbc.JdbcBackend.statement" level="DEBUG"/>
我有一个建立日志记录的示例项目 。 您将需要将xml文件(例如,Chapter-01文件夹)中的INFO
更改为DEBUG
。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.