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December 9, 2013

Grails Goodness: Using Closures for Select Value Rendering

To generate an HTML select we can use the Grails tag <g:select .../>. We use the optionValue attribute to specify a specific property we want to be used as the value. But we can also define a closure for the optionValue attribute to further customize the value that is shown to the user.

Suppose we have a simple domain class Book with a couple of properties. We want to combine multiple properties as the text for the HTML select options. In the following GSP we define first a <g:select .../> tag where we simply use the title property. In the next <g:select .../> tag we use a closure to combine multiple properties.

We can also pass the closure as model property to the GSP from a controller. In a controller we define the transformation in a closure and pass it along to the GSP page. On the GSP we can use this closure as a value for the optionValue attribute of the <g:select .../> tag. The following GSP shows all three scenarios.

<%@ page import="com.mrhaki.grails.sample.Book" contentType="text/html;charset=UTF-8" %>
<html>
<head>
    <title>Simple GSP page</title>
    <meta name="layout" content="main"/>
    <style>
        p { margin-top: 20px; margin-bottom: 5px;}
    </style>
</head>

<body>

    <h1>Select</h1>

    <p>Use title property of book for option values</p>

    <g:select from="${Book.list()}"
          optionKey="id"
          optionValue="title"
          name="bookSimple"/>

    <p>Use closure for optionValue</p>
    <g:select from="${Book.list()}"
              optionKey="id"
              optionValue="${{ book -> "${book.title} - ${book.isbn}" }}"
              name="bookCustom"/>

    <g:set var="bookOptionValueFormatter"
           value="${{ book -> "${book.title} (${book.isbn}, ${book.numberOfPages})" }}"/>

    <p>Use bookOptionValueFormatter that is defined as variable on this page</p>
    <g:select from="${Book.list()}"
              optionKey="id"
              optionValue="${bookOptionValueFormatter}"
              name="bookVar"/>

    <p>Use bookFormatter that is passed as a model property from SampleController.</p>
    <g:select from="${Book.list()}"
              optionKey="id"
              optionValue="${bookFormatter}"
              name="bookModel"/>

</body>


</html>

Here is a sample controller which passes the transformation to the GSP:

package com.mrhaki.grails.sample

class SampleController {

    def index() {
        final formatter = { book -> "$book.title (pages: $book.numberOfPages)" }
        [bookFormatter: formatter]
    }
}

When we run the application and open the page in a web browser we get the following HTML source:

...
<h1>Select</h1>

<p>Use title property of book for option values</p>

<select name="bookSimple" id="bookSimple" >
  <option value="1" >It</option>
  <option value="2" >The Stand</option>
</select>

<p>Use closure for optionValue</p>
<select name="bookVar" id="bookCustom" >
  <option value="1" >It - 0451169514</option>
  <option value="2" >The Stand - 0307743683</option>
</select>

<p>Use bookOptionValueFormatter that is defined as variable on this page</p>
<select name="bookVar" id="bookVar" >
  <option value="1" >It (0451169514, 1104)</option>
  <option value="2" >The Stand (0307743683, 1472)</option>
</select>

<p>Use bookFormatter that is passed as a model property from SampleController.</p>
<select name="bookModel" id="bookModel" >
  <option value="1" >It (pages: 1104)</option>
  <option value="2" >The Stand (pages: 1472)</option>
</select>
...

The optionKey attribute also allows closures as arguments.

Code written with Grails 2.3.2.