In my last post we created very simple Grails project and deployed it on Google Application Engine. Now we will try to extend it to use Google Datastore for persistence.
Configuration
Create a project in the same way as in previous post but ensure you will choose JPA as a persistence provider. Another option is JDO but I simply don't know this technology;)
Next step will be to install gorm-jpa plugin for Grails:
grails install-plugin gorm-jpa
Application goals
We will create very simple one page application to manage list of books. On the top there will be a list of book items. At the bottom there will a form to store new ones.
Implementation
We should create class for our domain object - grails-app\domain\test\Book.groovy:
package test
import javax.persistence.*;
@Entity
class Book implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
Long id
String title
static constraints = {
id visible:false
}
}
We need also web controller that will be responsible for 3 web actions:- index - main action listing all books
- save - adding new book
- remove - removing book
import test.*
class BookController {
def index = {
[books : Book.list( params )]
}
def save = {
Book b=new Book(params)
b.save()
redirect(action : index)
}
def remove = {
Book b=Book.get(params.id)
b.delete()
redirect(action : index)
}
}
Finally add GSP page (grails-app\views\book\index.gsp) that will present data and invoke particular actions of our controller:<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<meta name="layout" content="main" />
<title></title>
</head>
<body>
<h1>Books:</h1>
<table>
<thead>
<tr>
<th>Id</th>
<th>Title</th>
<th></th>
</tr>
</thead>
<g:each in="${books}" status="i" var="book">
<tr>
<td>${book.id}</td>
<td>${book.title}</td>
<td><g:link action="remove" id="${book.id}">remove</g:link> </td>
</tr>
</g:each>
</table>
<h1>New:</h1>
<g:form action="save">
<table>
<tr>
<td>Title</td>
<td><g:textField name="title" /></td>
</tr>
<tr>
<td colspan="2"><input type="submit" /></td>
</tr>
</table>
</g:form>
</body>
</html>
Deploy the application just as we did it in last post. Point the browser to /book resource of your web app. You should see our page running.Now, you can also browse datastore on GAE account pages:
Very useful posts, thankyou, this has got me started with GAE.
ReplyDeletei think it won't work with on-to-many relationships when id type is long. you'd need to do the following
ReplyDelete@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Extension(vendorName = "datanucleus", key = "gae.encoded-pk", value = "true")
String id
regards,
wojciech (your new colleague)