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A Scala ORM and DSL for talking with Databases using minimum verbosity and maximum type safety
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/*******************************************************************************
 * Copyright 2010 Maxime Lévesque
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 ***************************************************************************** */
package org.squeryl

import dsl.ast._
import internals.ResultSetMapper
import java.sql.ResultSet

trait Query[R] extends Queryable[R] {

  def iterator: Iterator[R]

  protected[squeryl] def invokeYield(rsm: ResultSetMapper, resultSet: ResultSet): R

  def dumpAst: String

  /**
   * returns a 'pretty' statement, i.e. values are printed instead of '?'  
   */
  def statement: String

  def ast: ExpressionNode

  private[squeryl] def copy(asRoot: Boolean, newUnions: List[(String, Query[R])]): Query[R]

  /**
   * Returns the first row of the query. An exception will be thrown
   * if the query returns no row or more than one row.
   */
  def single: R = {
    val i = iterator
    val r = i.next()
    if (i.hasNext)
      org.squeryl.internals.Utils.throwError("single called on query returning more than one row : \n" + statement)
    r
  }

  /**
   * Returns Some(singleRow), None if there are none, throws an exception 
   * if the query returns more than one row.
   */
  def singleOption: Option[R] = {
    val i = iterator
    val res =
      if (i.hasNext)
        Some(i.next())
      else
        None

    if (i.hasNext)
      org.squeryl.internals.Utils
        .throwError("singleOption called on query returning more than one row : \n" + statement)
    res
  }

  def headOption = {
    val i = iterator
    if (i.hasNext)
      Some(i.next())
    else
      None
  }

  def union(q: Query[R]): Query[R]

  def unionAll(q: Query[R]): Query[R]

  def intersect(q: Query[R]): Query[R]

  def intersectAll(q: Query[R]): Query[R]

  def except(q: Query[R]): Query[R]

  def exceptAll(q: Query[R]): Query[R]

  def distinct: Query[R]

  def forUpdate: Query[R]

  def page(offset: Int, pageLength: Int): Query[R]

  private[squeryl] def root: Option[Query[R]] = None
}