Scala Slick，仅在不存在时如何创建模式

Question

在 Scala Slick 中，可以使用以下内容创建数据库模式：

val schema = coffees.schema ++ suppliers.schema
db.run(DBIO.seq(
  schema.create
))

来自本文档页面底部http://slick.typesafe.com/doc/3.0.0/schemas.html

但是，如果数据库架构已经存在，那么这会引发异常。

是否有正常的方式或正确的方式来创建架构，如果且仅当架构不存在时？

Answer 1

在 Slick 3.3.0 中添加了 createIfNotExists 和 dropIfExists 架构方法。所以：

db.run(coffees.schema.createIfNotExists)

在 Google 上搜索了这个问题，并尝试了几种解决方案，直到弄明白为止。

Answer 2

这是我为多个表所做的，使用 slick 3.1.1 和 Postgres

import slick.driver.PostgresDriver.api._
import slick.jdbc.meta.MTable
import scala.concurrent.Await
import scala.concurrent.duration.Duration
import scala.concurrent.ExecutionContext.Implicits.global

val t1 = TableQuery[Table1]
val t2 = TableQuery[Table2]
val t3 = TableQuery[Table3]
val tables = List(t1, t2, t3)

val existing = db.run(MTable.getTables)
val f = existing.flatMap( v => {
    val names = v.map(mt => mt.name.name)
    val createIfNotExist = tables.filter( table =>
        (!names.contains(table.baseTableRow.tableName))).map(_.schema.create)
    db.run(DBIO.sequence(createIfNotExist))
})
Await.result(f, Duration.Inf)

Answer 3

在 Slick 3.0 中，Mtable.getTables 是 DBAction，所以这样的东西可以工作：

val coffees = TableQuery[Coffees]
try {
  Await.result(db.run(DBIO.seq(
    MTable.getTables map (tables => {
      if (!tables.exists(_.name.name == coffees.baseTableRow.tableName))
        coffees.schema.create
    })
  )), Duration.Inf)
} finally db.close

Answer 4

正如JoshSGoman comment 指出的关于answer of Mike-s 的那样，没有创建表。我设法通过稍微修改第一个答案的代码使其工作：

val coffees = TableQuery[Coffees]

try {
  def createTableIfNotInTables(tables: Vector[MTable]): Future[Unit] = {
    if (!tables.exists(_.name.name == events.baseTableRow.tableName)) {
      db.run(coffees.schema.create)
    } else {
      Future()
    }
  }

  val createTableIfNotExist: Future[Unit] = db.run(MTable.getTables).flatMap(createTableIfNotInTables)

  Await.result(createTableIfNotExist, Duration.Inf)
} finally db.close

使用以下导入：

import slick.jdbc.meta.MTable
import slick.driver.SQLiteDriver.api._

import scala.concurrent.{Await, Future}
import scala.concurrent.duration.Duration
import scala.concurrent.ExecutionContext.Implicits.global

Answer 5

你为什么不简单地检查create之前的存在？

val schema = coffees.schema ++ suppliers.schema
db.run(DBIO.seq(
  if (!MTable.getTables.list.exists(_.name.name == MyTable.tableName)){
    schema.create
  }
))

Answer 6

不能对由 3 个表组成的架构使用 createIfNotExists，其中一个表具有复合主键。这里，第 3 表具有由第 1 表和第 2 表各自的主键组成的主键。当第二次遇到 .createIfNotExists 时，我在此架构上遇到错误。我在 scala 2.12.8 上使用 slick 3.3.1。

    class UserTable(tag: Tag) extends Table[User](tag, "user") {
      def id    = column[Long]("id", O.AutoInc, O.PrimaryKey)
      def name  = column[String]("name")
      def email = column[Option[String]]("email")

      def * = (id.?, name, email).mapTo[User]
    }
    val users = TableQuery[UserTable]
    lazy val insertUser = users returning users.map(_.id)

    case class Room(title: String, id: Long = 0L)
    class RoomTable(tag: Tag) extends Table[Room](tag, "room") {
     def id    = column[Long]("id", O.PrimaryKey, O.AutoInc)
     def title = column[String]("title")
     def * = (title, id).mapTo[Room]
    }
    val rooms = TableQuery[RoomTable]
    lazy val insertRoom = rooms returning rooms.map(_.id)

    case class Occupant(roomId: Long, userId: Long)
    class OccupantTable(tag: Tag) extends Table[Occupant](tag, "occupant") {
      def roomId = column[Long]("room")
      def userId = column[Long]("user")

      def pk = primaryKey("room_user_pk", (roomId, userId) )

      def * = (roomId, userId).mapTo[Occupant]
    }
    val occupants = TableQuery[OccupantTable]

我可以成功创建架构并首先添加用户、房间和居住者。在 .createIfNotExists 的第二次使用中，如下所示，我收到重复主键错误：

  println("\n2nd run on .createIfNotExists using different values for users, rooms and occupants")
  val initdup = for {
    _         <- users.schema.createIfNotExists
    _         <- rooms.schema.createIfNotExists
    _         <- occupants.schema.createIfNotExists
      curlyId   <- insertUser += User(None, "Curly", Some("curly@example.org"))
      larryId   <- insertUser += User(None, "Larry")
      moeId     <- insertUser += User(None, "Moe", Some("moe@example.org"))
      shedId   <- insertRoom += Room("Shed")
      _         <- occupants += Occupant(shedId, curlyId)
      _         <- occupants += Occupant(shedId, moeId)
    } yield ()

例外情况如下：

2nd run on .createIfNotExists using different values for users, rooms and occupants
[error] (run-main-2) org.h2.jdbc.JdbcSQLException: Constraint "room_user_pk" already exists; SQL statement:
[error] alter table "occupant" add constraint "room_user_pk" primary key("room","user") [90045-197]
[error] org.h2.jdbc.JdbcSQLException: Constraint "room_user_pk" already exists; SQL statement:
[error] alter table "occupant" add constraint "room_user_pk" primary key("room","user") [90045-197]
[error]         at org.h2.message.DbException.getJdbcSQLException(DbException.java:357)
[error]         at org.h2.message.DbException.get(DbException.java:179)
[error]         at org.h2.message.DbException.get(DbException.java:155)
[error]         at org.h2.command.ddl.AlterTableAddConstraint.tryUpdate(AlterTableAddConstraint.java:110)
[error]         at org.h2.command.ddl.AlterTableAddConstraint.update(AlterTableAddConstraint.java:78)
[error]         at org.h2.command.CommandContainer.update(CommandContainer.java:102)
[error]         at org.h2.command.Command.executeUpdate(Command.java:261)
[error]         at org.h2.jdbc.JdbcPreparedStatement.execute(JdbcPreparedStatement.java:249)
[error]         at slick.jdbc.JdbcActionComponent$SchemaActionExtensionMethodsImpl$$anon$6.$anonfun$run$7(JdbcActionComponent.scala:292)
[error]         at slick.jdbc.JdbcActionComponent$SchemaActionExtensionMethodsImpl$$anon$6.$anonfun$run$7$adapted(JdbcActionComponent.scala:292)
[error]         at slick.jdbc.JdbcBackend$SessionDef.withPreparedStatement(JdbcBackend.scala:425)
[error]         at slick.jdbc.JdbcBackend$SessionDef.withPreparedStatement$(JdbcBackend.scala:420)
[error]         at slick.jdbc.JdbcBackend$BaseSession.withPreparedStatement(JdbcBackend.scala:489)
[error]         at slick.jdbc.JdbcActionComponent$SchemaActionExtensionMethodsImpl$$anon$6.$anonfun$run$6(JdbcActionComponent.scala:292)
[error]         at slick.jdbc.JdbcActionComponent$SchemaActionExtensionMethodsImpl$$anon$6.$anonfun$run$6$adapted(JdbcActionComponent.scala:292)
[error]         at scala.collection.Iterator.foreach(Iterator.scala:941)
[error]         at scala.collection.Iterator.foreach$(Iterator.scala:941)
[error]         at scala.collection.AbstractIterator.foreach(Iterator.scala:1429)
[error]         at scala.collection.IterableLike.foreach(IterableLike.scala:74)
[error]         at scala.collection.IterableLike.foreach$(IterableLike.scala:73)
[error]         at scala.collection.AbstractIterable.foreach(Iterable.scala:56)
[error]         at slick.jdbc.JdbcActionComponent$SchemaActionExtensionMethodsImpl$$anon$6.run(JdbcActionComponent.scala:292)
[error]         at slick.jdbc.JdbcActionComponent$SchemaActionExtensionMethodsImpl$$anon$6.run(JdbcActionComponent.scala:290)
[error]         at slick.jdbc.JdbcActionComponent$SimpleJdbcProfileAction.run(JdbcActionComponent.scala:28)
[error]         at slick.jdbc.JdbcActionComponent$SimpleJdbcProfileAction.run(JdbcActionComponent.scala:25)
[error]         at slick.basic.BasicBackend$DatabaseDef$$anon$3.liftedTree1$1(BasicBackend.scala:276)
[error]         at slick.basic.BasicBackend$DatabaseDef$$anon$3.run(BasicBackend.scala:276)
[error]         at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
[error]         at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
[error]         at java.lang.Thread.run(Thread.java:748)
[error] Nonzero exit code: 1
[error] (Compile / run) Nonzero exit code: 1

此外，我可以在使用 O.PrimaryKey 约定创建所有表的架构上多次使用 .createIfNotExists。

我可以做些什么来按摩代码吗？是否有解决方法使 .createIfNotExists 在复合主键情况下仍然可用？