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" %>
...

Select

Use title property of book for option values

Use closure for optionValue

Use bookOptionValueFormatter that is defined as variable on this page

Use bookFormatter that is passed as a model property from SampleController.

...

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:

...

Select

Use title property of book for option values

It The Stand

Use closure for optionValue

It - 0451169514 The Stand - 0307743683

Use bookOptionValueFormatter that is defined as variable on this page

It (0451169514, 1104) The Stand (0307743683, 1472)

Use bookFormatter that is passed as a model property from SampleController.

It (pages: 1104) The Stand (pages: 1472) ...

The optionKey attribute also allows closures as arguments.

Code written with Grails 2.3.2.

Original article

shadow-left