我尝试使用https://github.com/slick/slick-examples/blob/master/src/main/scala/scala/slick/examples/lifted/FirstExample.scala中的示例数据库构建计数查询：
// Definition of the SUPPLIERS table
object Suppliers extends Table[(Int, String, String, String, String, String)]("SUPPLIERS") {
def id = column[Int]("SUP_ID", O.PrimaryKey) // This is the primary key column
def name = column[String]("SUP_NAME")
def street = column[String]("STREET")
def city = column[String]("CITY")
def state = column[String]("STATE")
def zip = column[String]("ZIP")
// Every table needs a * projection with the same type as the table's type parameter
def * = id ~ name ~ street ~ city ~ state ~ zip
}
// Definition of the COFFEES table
object Coffees extends Table[(String, Int, Double, Int, Int)]("COFFEES") {
def name = column[String]("COF_NAME", O.PrimaryKey)
def supID = column[Int]("SUP_ID")
def price = column[Double]("PRICE")
def sales = column[Int]("SALES")
def total = column[Int]("TOTAL")
def * = name ~ supID ~ price ~ sales ~ total
// A reified foreign key relation that can be navigated to create a join
def supplier = foreignKey("SUP_FK", supID, Suppliers)(_.id)
}
// Connect to the database and execute the following block within a session
Database.forURL("jdbc:h2:mem:test1", driver = "org.h2.Driver") withSession {
(Suppliers.ddl ++ Coffees.ddl).create
// Insert some suppliers
Suppliers.insert(101, "Acme, Inc.", "99 Market Street", "Groundsville", "CA", "95199")
Suppliers.insert( 49, "Superior Coffee", "1 Party Place", "Mendocino", "CA", "95460")
Suppliers.insert(150, "The High Ground", "100 Coffee Lane", "Meadows", "CA", "93966")
// Insert some coffees (using JDBC's batch insert feature, if supported by the DB)
Coffees.insertAll(
("Colombian", 101, 7.99, 0, 0),
("French_Roast", 49, 8.99, 0, 0),
("Espresso", 150, 9.99, 0, 0),
("Colombian_Decaf", 101, 8.99, 0, 0),
("French_Roast_Decaf", 49, 9.99, 0, 0)
)
/**** This part works fine */
val query = for (c <- Coffees) yield c
query foreach println
/*********/
/******This one fails */
val query1 = for (c <- Coffees) yield c.length
println("query1 = " + query1.list.head)
提出的错误H2是：
Column "X4.COF_NAME" not found; SQL statement:
CREATE FORCE VIEW PUBLIC._1 AS
SELECT
X4.COF_NAME,
X4.SUP_ID,
X4.PRICE,
X4.SALES,
X4.TOTAL
FROM SYSTEM_RANGE(1, 1) [42122-168]
org.h2.jdbc.JdbcSQLException: Column "X4.COF_NAME" not found; SQL statement:
CREATE FORCE VIEW PUBLIC._1 AS
SELECT
X4.COF_NAME,
X4.SUP_ID,
X4.PRICE,
X4.SALES,
X4.TOTAL
FROM SYSTEM_RANGE(1, 1) [42122-168]
at org.h2.message.DbException.getJdbcSQLException(DbException.java:329)
at org.h2.message.DbException.get(DbException.java:169)
at org.h2.message.DbException.get(DbException.java:146)
at org.h2.expression.ExpressionColumn.optimize(ExpressionColumn.java:138)
at org.h2.command.dml.Select.prepare(Select.java:799)
at org.h2.command.Parser.prepare(Parser.java:202)
at org.h2.engine.Session.prepare(Session.java:388)
at org.h2.engine.Session.prepare(Session.java:375)
at org.h2.table.TableView.compileViewQuery(TableView.java:99)
at org.h2.table.TableView.initColumnsAndTables(TableView.java:144)
at org.h2.table.TableView.init(TableView.java:95)
at org.h2.table.TableView.(TableView.java:61)
at org.h2.table.TableView.createTempView(TableView.java:420)
at org.h2.command.Parser.readTableFilter(Parser.java:1037)
at org.h2.command.Parser.parseSelectSimpleFromPart(Parser.java:1690)
at org.h2.command.Parser.parseSelectSimple(Parser.java:1797)
at org.h2.command.Parser.parseSelectSub(Parser.java:1684)
at org.h2.command.Parser.parseSelectUnion(Parser.java:1527)
at org.h2.command.Parser.readTableFilter(Parser.java:1026)
at org.h2.command.Parser.parseSelectSimpleFromPart(Parser.java:1690)
at org.h2.command.Parser.parseSelectSimple(Parser.java:1797)
at org.h2.command.Parser.parseSelectSub(Parser.java:1684)
at org.h2.command.Parser.parseSelectUnion(Parser.java:1527)
at org.h2.command.Parser.parseSelect(Parser.java:1515)
at org.h2.command.Parser.parsePrepared(Parser.java:405)
at org.h2.command.Parser.parse(Parser.java:279)
at org.h2.command.Parser.parse(Parser.java:251)
at org.h2.command.Parser.prepareCommand(Parser.java:217)
at org.h2.engine.Session.prepareLocal(Session.java:415)
at org.h2.engine.Session.prepareCommand(Session.java:364)
at org.h2.jdbc.JdbcConnection.prepareCommand(JdbcConnection.java:1109)
at org.h2.jdbc.JdbcPreparedStatement.(JdbcPreparedStatement.java:74)
at org.h2.jdbc.JdbcConnection.prepareStatement(JdbcConnection.java:626)
at scala.slick.session.Session$class.prepareStatement(Session.scala:29)
at scala.slick.session.BaseSession.prepareStatement(Session.scala:201)
at scala.slick.jdbc.StatementInvoker.results(StatementInvoker.scala:29)
at scala.slick.jdbc.StatementInvoker.elementsTo(StatementInvoker.scala:17)
at scala.slick.jdbc.Invoker$class.foreach(Invoker.scala:90)
at scala.slick.jdbc.StatementInvoker.foreach(StatementInvoker.scala:10)
at scala.slick.jdbc.Invoker$class.build(Invoker.scala:66)
at scala.slick.jdbc.StatementInvoker.build(StatementInvoker.scala:10)
at scala.slick.jdbc.Invoker$class.list(Invoker.scala:56)
at scala.slick.jdbc.StatementInvoker.list(StatementInvoker.scala:10)
at scala.slick.jdbc.UnitInvoker$class.list(Invoker.scala:150)
at scala.slick.driver.BasicInvokerComponent$QueryInvoker.list(BasicInvokerComponent.scala:19)
是由于使用错误？这是一个错误吗？
如果我使用
，则会引发错误println("query1 = " + query1.firstOption.getOrElse(0))
以及......
答案 0 :(得分：3)
您是否尝试过以下操作？
val query1 = for (c <- Coffees) yield c.name.count
println("query1 = " + query1.firstOption.getOrElse(0))
背后的秘诀是c.primary-key.count;在这种情况下，name是Coffees的主键。