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From: chinmaykolhatkar <git@git.apache.org>
To: dev@apex.incubator.apache.org
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References: <git-pr-209-incubator-apex-malhar@git.apache.org>
In-Reply-To: <git-pr-209-incubator-apex-malhar@git.apache.org>
Subject: [GitHub] incubator-apex-malhar pull request: APEXMALHAR-2010 Add
 Tranform o...
Content-Type: text/plain
Message-Id: <20160321063116.AFA55DFB7D@git1-us-west.apache.org>
Date: Mon, 21 Mar 2016 06:31:16 +0000 (UTC)

Github user chinmaykolhatkar commented on a diff in the pull request:

    https://github.com/apache/incubator-apex-malhar/pull/209#discussion_r56785718
  
    --- Diff: library/src/main/java/com/datatorrent/lib/util/PojoUtils.java ---
    @@ -696,11 +662,97 @@ private static Object createSetter(Class<?> pojoClass, String setterExpr, String
           code = getSingleFieldSetterExpression(pojoClass, setterExpr, exprClass);
         }
     
    +    return compileExpression(code, setterClass, new String[] {PojoUtils.OBJECT, PojoUtils.VAL});
    +  }
    +
    +  /**
    +   * This method takes in expression, compiles the expression to provide a executable form of expression.
    +   * This method uses {@link com.datatorrent.lib.expression.JavaExpressionParser} as expression parser.
    +   *
    +   * @param inputType  Type of input object
    +   * @param expr       expression to be compiled.
    +   * @param returnType Return type of the expression.
    +   * @return Object of type {@link Expression} which can be directly executed.
    +   */
    +  public static Expression createExpression(Class<?> inputType, String expr, Class<?> returnType)
    +  {
    +    return createExpression(inputType, expr, returnType, null);
    +  }
    +
    +  /**
    +   * This method takes in expression, compiles the expression to provide a executable form of expression.
    +   * This methods also takes in list of classes and method which can be imported statically in expression.
    +   * <p/>
    +   * This method uses {@link JavaExpressionParser} as expression parser.
    +   *
    +   * @param inputType      Type of input object
    +   * @param expr           expression to be compiled.
    +   * @param returnType     Return type of the expression.
    +   * @param defaultImports List of classes/method which will be statically imported to expression compilation.
    +   * @return Object of type {@link Expression} which can be directly executed.
    +   */
    +  public static Expression createExpression(Class<?> inputType, String expr, Class<?> returnType,
    +      String[] defaultImports)
    +  {
    +    JavaExpressionParser javaExpressionParser = new JavaExpressionParser();
    +    javaExpressionParser.setInputObjectPlaceholder("$", PojoUtils.OBJECT);
    +
    +    return createExpression(inputType, expr, returnType, defaultImports, javaExpressionParser);
    +  }
    +
    +  /**
    +   * This method takes in expression, compiles the expression to provide a executable form of expression.
    +   * This methods also takes in list of classes and method which can be imported statically in expression.
    +   * <p/>
    +   * Using this method one can override expression parser implementation.
    +   *
    +   * @param inputType      Type of input object
    +   * @param expr           expression to be compiled.
    +   * @param returnType     Return type of the expression.
    +   * @param defaultImports List of classes/method which will be statically imported to expression compilation.
    +   * @param parser         Expression parser that should be used to parse expression.
    +   * @return Object of type {@link Expression} which can be directly executed.
    +   * @see {@link JavaExpressionParser} as a example.
    +   */
    +  public static Expression createExpression(Class<?> inputType, String expr, Class<?> returnType,
    +      String[] defaultImports, Expression.ExpressionParser parser)
    +  {
    +    String code = parser.convertToCompilableExpression(expr, inputType, returnType);
    +
    +    return (Expression)compileExpression(code, Expression.class, new String[] {PojoUtils.OBJECT}, defaultImports);
    +  }
    +
    +  private static Object compileExpression(String code, Class<?> implClass, String[] params)
    +  {
    +    return compileExpression(code, implClass, params, null);
    +  }
    +
    +  private static Object compileExpression(String code, Class<?> implClass, String[] params, String[] defaultImports)
    +  {
    +    List<String> imports = new LinkedList<>();
    +    if (defaultImports != null && defaultImports.length != 0) {
    +      for (String defaultImport : defaultImports) {
    +        if (!defaultImport.startsWith("static")) {
    --- End diff --
    
    When adding a given import as static, that means the method will be directly available in expression to be used. This way, the expression writer can use similar syntax like excel functions.


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