Anorm用法

什麼是Anrom

用作寫SQL,但免去JDBC 麻煩的煩惱,典型的JDBC需要create statement/PreparedStatement 師很多try catch,Anorm還簡化了煩人的resultset looping 以及如何將resultset的內容提取

From Java Tutorial {% codeblock %} public void updateCoffeeSales(HashMap<String, Integer> salesForWeek) throws SQLException {

PreparedStatement updateSales = null;
PreparedStatement updateTotal = null;

String updateString =
    "update " + dbName + ".COFFEES " +
    "set SALES = ? where COF_NAME = ?";

String updateStatement =
    "update " + dbName + ".COFFEES " +
    "set TOTAL = TOTAL + ? " +
    "where COF_NAME = ?";

try {
    con.setAutoCommit(false);
    updateSales = con.prepareStatement(updateString);
    updateTotal = con.prepareStatement(updateStatement);

    for (Map.Entry<String, Integer> e : salesForWeek.entrySet()) {
        updateSales.setInt(1, e.getValue().intValue());
        updateSales.setString(2, e.getKey());
        updateSales.executeUpdate();
        updateTotal.setInt(1, e.getValue().intValue());
        updateTotal.setString(2, e.getKey());
        updateTotal.executeUpdate();
        con.commit();
    }
} catch (SQLException e ) {
    JDBCTutorialUtilities.printSQLException(e);
    if (con != null) {
        try {
            System.err.print("Transaction is being rolled back");
            con.rollback();
        } catch(SQLException excep) {
            JDBCTutorialUtilities.printSQLException(excep);
        }
    }
} finally {
    if (updateSales != null) {
        updateSales.close();
    }
    if (updateTotal != null) {
        updateTotal.close();
    }
    con.setAutoCommit(true);
}

} {% endcodeblock %}

使用方法

在build.sbt 加入 {% codeblock %} libraryDependencies ++= Seq( jdbc, "com.typesafe.play" %% "anorm" % "2.4.0" ) {% endcodeblock %}

在program中加入 {% codeblock lang:scala %} import anorm._ import play.api.db.DB

DB.withConnection { implicit c => val result: Boolean = SQL("Select 1").execute() } {% endcodeblock %}

{% codeblock lang:scala %} 如果你擔心有exception 可以wrap 在try catch內 try {

} catch { case ex: Exception =˃ ex.getMessage } {% endcodeblock %}

DB是playframework的datasource

執行query

SQL("Select 1") 常用以下各種method

  • execute() : 用作any query, 回傳一個Boolean, true 代表提取了resultset
  • executeUpdate() : 用作update, insert, delete, 回傳受影響的行數
  • executeInsert() : 用作插入資料, 回傳一個Option[Long] 作用generated ID
  • executeQuery() : 用作提取資料, 回傳SqlQueryResult (資料褲內容) 詳見Reference 2

在SQL 插入數值

Anrom提供方法簡化 PreparedStatement煩複的setXXXX updateSales.setInt(1, e.getValue().intValue()); updateSales.setString(2, e.getKey());

方法1: 使用on

{% codeblock lang:scala %} SQL( """ select * from Country c join CountryLanguage l on l.CountryCode = c.Code where c.code = {countryCode} """) .on("countryCode" -> "FRA") {% endcodeblock %} {countryCode} 的數值變為 "FRA"

方法2: 使用String Interpolation (Scala > 2.10)

{% codeblock %} val name = "Cambridge" val country = "New Zealand"

SQL"insert into City(name, country) values ($name, $country)" {% endcodeblock %} 將name的數值插中$name 當中

提取資料

這裡的API有點難理解, 請先import import anorm.SqlParser._ 以使用built in parser

其中一項SQL最常用的功能為提取資料, Anorm 抽取了將SQLQueryResult (ResultSet)變為所需資料的過程, 我們最終需要ResultSetParser,但ResultSetParserRowParser轉換而來

  • RowParser 將column data變為我們所需的data
  • ResultSetParser 定義如何parse resultSet,例如不同行數會回傳不同data

例子

{% codeblock %} val count: Long = SQL("select count(*) from Country").as(scalar[Long].single) {% endcodeblock %}

as會自動執行executeQuery() 然後將結果給parser用作提取資料 當中RowParser是 scalar[Long], scalar是anorm中用作唯一column的parser,將count(*)變為Long 當中ResultSetParser是scalar[Long].single api 中定義為def single: ResultSetParser[A], 因此return Long

利用column name的parser

{% codeblock %} val populations: List[String ~ Int] = SQL("SELECT * FROM Country").as((str("name") ~ int("population")).) {% endcodeblock %} str("name") 將name 轉換String, int("population") 將population 轉換為int, 每行結果為String ~ Int `代表很多行, 所以總結果為List[String ~ Int]`

String ~ Int 是anorm定義的type, 可用pattern matching 進行轉換 {% codeblock %} val parser = str("name") ~ int("population") map { case n ~ p => (n, p) } {% endcodeblock %}

將RowParser轉換為ResultSetParser

  • single: ResultSetParser[A], Returns a result set parser expecting exactly one row to parse.
  • singleOpt: ResultSetParser[Option[A]], Returns a result set parser for none or one parsed row.
  • *: ResultSetParser[List[A]], Returns possibly empty list parsed from result.
  • +: ResultSetParser[List[A]], Returns non empty list parse from result, or raise error if there is no result.
  • ?: RowParser[Option[A]], Returns a row parser for optional column, that will turn missing or null column as None.

Reference

  1. Play 2.4 Anrom Introduction
  2. Simple SQL API
  3. ResultSetParser API
  4. Anorm built in rowParser API