Carol McDonald's Blog: Sample Store Catalog using using Groovy and Grails

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Sample Store Catalog using using Groovy and Grails

Posted by caroljmcdonald on April 28, 2008 at 07:35 PM | Comments (3)

grailsexample

Sample Store Catalog using using Groovy and Grails

This Catalog Sample app demonstrates the usage of Groovy and Grails to implement pagination of data sets for a Store Catalog.
download Catalog sample code

Overview of the Technologies and Frameworks in the Sample Application

Grails aims to bring the "coding by convention" paradigm to Groovy. It's an open-source web application framework that leverages the Groovy language and complements Java Web development.

Groovy is an agile and dynamic language for the Java Virtual Machine, it compiles to Java bytecode, and it combines popular features from languages such as Smalltalk, Python, and Ruby.

Grails is a Model-View-Controller based framework that simplifies the development of web applications by reducing the need for configuration files and by generating a lot of the things needed in a database-backed Web application.

The Sample Application

The sample application displays an online catalog of pets sold in a pet store. The image below shows the Catalog Listing page, which allows a user to page through a list of items in a store.

The Model - Grails Domain Classes

The Model is your application's persistent business domain objects. A Grails domain object instance represents a row in a database table. The command

grails
create-domain-class Item

generates the Item.groovy class shown below corresponding to the item table.

After model code generation you have to add the domain object's attributes and relationships. The Item class has a many-to-one relationship with the Address class. In Grails hasMany is the many end of a many-to-one relationship.

Code Sample from: domain\Item.groovy



class Item
{

  Long id

  String name

  String description

  String imageurl

  String imagethumburl

  BigDecimal price

  Address
            address

}

Code Sample from: domain\Address.groovy



class Address
{

  Long id 

  String street1 

  String street2 

  String city 

  String state 

  String zip 

  float latitude 

  float longitude 

  static
hasMany = [item:Item]

}

SQL Sample for items table



CREATE TABLE item (

 id BIGINT NOT NULL,

 product_id BIGINT NOT NULL,

 name VARCHAR(30) NOT NULL,

 description VARCHAR(500) NOT NULL,

 imageurl VARCHAR(55),

 imagethumburl VARCHAR(55),

 price DECIMAL(14,2) NOT NULL,

 address_id BIGINT NOT NULL,

 primary key (id),

 foreign key (address_id) references address(id),

 foreign key (product_id) references product(id)

);

Groovy with Grails dynamically generates getters and setters and the dynamic methods Item.save(), Item.delete(), Item.list(), Item.get() to retrieve/update data from/to the db table.

Grails Object Relational Mapping (GORM) is currently built on top of Hibernate but you don't have to know Hibernate to use it ( Grails 1.1 will support the Java Persistence API) .

The Controller

Controllers handle incoming http requests, interact with the model to get data and to process requests, invoke the correct view, and direct domain data to the view for display. In Grails, http requests are handled by Controller classes which are made up of one or more action methods that are executed on request and then either render a Groovy Server Page or redirect to another action. Grails routes requests to the controller action which corresponds to the URL mapping for the request. In Grails the default mapping from URL to action method follows this convention: http://host/app/controller/action/id . For example the URL http://host/catalog/item/list calls the list action method in the item controller class shown below. Grails Scaffolding provides a series of standardized Controller action methods for listing, showing, creating, updating, and deleting objects of a class. These standardized actions come with both controller logic and default view Groovy Server Pages. The command generate-all Item generates the Item controller and the List, Show, Create, Edit Groovy Server Pages for the Item domain object. The ItemController list action renders a view with a paginated list of item objects.

Code Sample from: grails-app\controllers\ItemController.groovy

class ItemController {

def index = { redirect(action:list,params:params) }

def list = {
if(!params.max) params.max = 10
[ itemList: Item.list( params ) ]
}
. . .

When a URL has a controller but no action (e.g. http://localhost:8080/catalog/item/ ), Grails defaults to the index action. In the ItemController code the index action method redirects to the list action. The ItemController list action method calls the Item.list() method which returns an ArrayList of item objects retrieved from the item database table . If there are more than params.max objects in the table, Grails creates next and previous pagination links automatically. The itemList variable is automatically made available to the view by the framework.

After executing code, actions usually render a GSP in the views directory corresponding to the name of the controller and action, for example the list action will render the grails-app\views\item\list.gsp .

The View

The view layer generates a web page, using data from domain objects provided by the controller. In Grails, the view is rendered using Groovy Server Pages. Below is part of the list.gsp for the Catalog application (note I modified the html table format from the default generated).

Code Sample from: grails-app\views\item\list.gsp



<table>

   <thead>

     <tr>

        <g:sortableColumn
property="name" title="Name" />

        <g:sortableColumn
property="imagethumburl" title="Photo" />

        <g:sortableColumn
property="price" title="Price" />

     </tr>

   </thead>

   <tbody>

     <g:each
in="${itemList}"
status="i"
var="item">

        <tr class="${(i % 2) == 0
? 'odd' : 'even'}">

           <td>

            
      <g:link
action="show" id="${item.id}">

               
${item.name?.encodeAsHTML()}</g:link>

           </td>

           <td>

            
<img src="${createLinkTo(dir:'images',file:item.imagethumburl)}"/>

           </td>

          
<td>${item.price?.encodeAsHTML()}</td>

        </tr>

     </g:each>

  </tbody>

 </table>

      

<div class="paginateButtons">

 <g:paginate
total="${Item.count()}" />

</div>

The view uses instance variables set by the controller to access the data it needs to render the GSP.

GSP has a GroovyTagLib similar to the JSP tag library. <g: are GroovyTags.

<g:sortableColumn
The sortableColumn tag renders a sortable column to support sorting in tables.

<g:each
in="${itemList}" status="i"
var="item">

loops through each object in the itemList variable, which is an ordered ArrayList of Item model objects, and assigns each Item model object to the item variable.

<g:link
action="show"
id="${item.id}">${item.name?.encodeAsHTML()}</g:link>

the
<g:link>

GroovyTag creates an html anchor tag href based on the action, id, controller parameters specified. In this example it generates a link to the item/show/id action which when clicked will display the corresponding item details. For example this line will generate the following HTML for the variable item:

<a href="/catalog/item/show/2">Friendly Cat</a>

<img
src="${createLinkTo(dir:'images',file:item.imagethumburl)}"/>

The createLinkTo tag generates an HTML link for the

item's
imagethumburl

attribute.

${item.price?.encodeAsHTML()}

displays the value of the item 's price attribute as escaped HTML text.

<g:paginate
total="${Item.count()}" />

The paginate tag creates next/previous buttons and a breadcrumb trail to allow pagination of results using the Item.count() domain method.

The Show Action Method

In Grails the mapping for the URL http://host/item/show/1 ( http://host/controller/action/id ) will route to the show action in the ItemController passing 1 to the method as the id of the params parameter hash. The show action of the ItemController class is shown below. The ItemController show action renders a view showing the details of the item object corresponding to the id parameter.

Code Sample from: grails-app\controllers\ItemController.groovy

def show = {
   def item = Item.get( params.id )

   if(!item) {
      flash.message = "Item not found with id ${params.id}"
      redirect(action:list)
   }
   else { return [ item : item ] }
}

The show action method calls the Item.get() method which queries the items table returning the item instance variable corresponding to the item with the attribute id (primary key) equal to the id parameter. This is the equivalent of the following sql : select * from items where id='1' . The item variable is automatically made available to the Show view by the framework.

The Show View GSP

After executing code in the action, the show action renders the app/views/item/show.gsp . Below is the GSP for the item show view :

Code Sample from: grails-app\views\item\show.gsp

 

<h2> Detail of item</h2>

      

<table>

<tbody>

    <tr class="prop">

      <td valign="top"
class="name">Name:</td>                          
      

      <td valign="top"
class="value">${item.name}</td>                          
      

   
</tr>                   
      

    <tr class="prop">

        <td valign="top"
class="name">

          
Description:

       
</td>                           
      

        <td valign="top"
class="value">

          
${item.description}

       
</td>                          
      

   
</tr>                       
      

    <tr class="prop">

        <td valign="top"
class="name">Imageurl:</td>                          
      

        <td valign="top"
class="value">

           
<img src="${createLinkTo(dir:'images',file:item.imageurl)}"
/>

       
</td>                           
      

   
</tr>                                           
      

    <tr class="prop">

        <td valign="top"
class="name">Price:</td>                           
      

        <td valign="top"
class="value">$
${item.price}</td>                           
      

    </tr>

    <tr class="prop">

        <td valign="top"
class="name">Address:</td>                           
      

        <td valign="top"
class="value">

         
${item?.address?.street1},
${item?.address?.city},    
      

         
${item?.address?.state}

       
</td>                          
      

   
</tr>                       
      

</tbody>

</table>

${item.description}

displays the value of the item 's description attribute.

<img
src="${createLinkTo(dir:'images',file:item.imageurl)}" />

generates an HTML image tag for the item's imageurl attribute.


${item?.address?.city}

displays the value of the item's address city attribute.

The image below shows the resulting page for the url http://host/catalog/item/show/105, which displays the item 105's details:

Layouts

Grails layouts let you put common html on multiple views (for example page headers, footers, sidebars). Default layout templates are in the views layouts directory with a file name corresponding to the controller, or you can associate a view with a layout using the "layout" meta tag to your page:

<meta name="layout" content="main">

To add a title and parrot image to the top of the Pet Catalog pages, I put this table in the app\views\layouts\main.gsp layout:

Code Sample from: app/views/layouts/main.gsp

<table>
<tr>
   <td>Pet Catalog</td>
   <td>
     <img src="${createLinkTo(dir:'images',file:'pet_logo.jpg')}"/>
   </td>
</tr>
</table>

Conclusion
This concludes the sample application which demonstrates how to work with Groovy and Grails to page through a list of Item Model objects which are retrieved using Item Controller action methods, and displayed using Item View GSPs.

Setting Things Up and Running the Sample code on MySQL and Jetty:

If MySQL is already installed, then download GlassFish v2 UR1. Otherwise you can also Download GlassFish v2 UR1 and MySQL co-bundle from the usual Download Page (instructions).
Download and install Grails.
Download the sample code and extract its contents. You should now see the newly extracted directory as <sample_install_dir>/Catalog, where <sample_install_dir> is the directory where you unzipped the sample package. For example, if you extracted the contents to C:\ on a Windows machine, then your newly created directory should be at C:\Catalog.
The file "/Catalog/grails-app/conf/DataSource.groovy" is configured for a MySQL configuration.
Start the MySQL database as follows:
- > mysqld_safe --user root --console
Create the pet-catalog database:
- > mysqladmin create petcatalog --user root
Create the tables in the MySQL pet-catalog database as follows:
- ```
shell> mysql pet-catalog < catalog.sql
```
- using the file catalog.sql file from the /Catalog directory.
Run the project as follows:
in a command window in the /Catalog directory enter the command
```
> grails run-app
```
This will run the Application using the built-in Jetty Servlet engine.

When you run the project, your browser should display the Catalog home page at http://localhost:8080/catalog/ .

Run the Sample code on Glassfish:

Use the WAR file in <sample_install_dir>/Catalog/Catalog.waror Create a WAR file:
- ```
> grails war
```
Copy the WAR file (catalog-0.1.war) to your Glassfish installation "domains/domain/autodeploy" directory. (Start Glassfish and MySQL if you haven't already)
Enter the URL http://localhost:8080/catalog-0.1/ in your browser, you should see the home page of the Sample Application.

References

To learn how to build a Grails CRUD app see: TOTD #30: CRUD Application using Grails - Hosted on Jetty and HSQLDB
To learn how to run a Grails app on Glassfish and mySQL see: TOTD #31: CRUD Application using Grails - Hosted on GlassFish and MySQL
Grails framework
Groovy
MySQL commands

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Comments

Comments are listed in date ascending order (oldest first) | Post Comment

Excellent article! Thanks a lot.
Posted by: guillaumelaforge on April 29, 2008 at 12:35 AM

You may also want to take a look at the Grails Pet Store.
Posted by: peter_backlund on April 29, 2008 at 07:42 AM

Thanks, yes that's interesting. My example isn't meant to be a Pet Store port btw, just a simple sample online catalog using grails. I've done similar sample online catalogs using Java EE, Spring, Seam, VWP, JRuby, Jmaki
Posted by: caroljmcdonald on April 29, 2008 at 07:50 AM

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