Dynamic Web Development with Seaside

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25.4.2Getting Started

You can install Magma using SqueakSource as indicated from http://wiki.squeak.org/squeak/2657. You basically get three packages, the client, the server and the tests. Typically you will load the server package, since the client package contains the code to connect to a remote server and the server package contains the client and server code.

To start we will work with a local repository. Later we describe the simple steps to do to get a remote server. Note that the difference between the two setups is quite small. We will define a small class to group all the operations to set up and manage a connection as well as accessing the session.

Setting up the Database. The first action is to set up the database using the message #create:root:. We have to give a file location and a root of the object graph we want to store in this location.

MagmaRepositoryController create: 'todo' root: ToDoList new.

Here the controller will create a repository in the path{/tmp/todo} folder and it takes the singleton of the ToDoList class since it contains all the items of our application. It is often the case that you specify a dictionary where you can define multiple roots of your application. We will use such code in the class that will manage the storage of our application.

Object subclass: #ToDoDB
instanceVariableNames: 'session'
classVariableNames: 'Default'
poolDictionaries: ''
category: 'ToDo-Model'

We define the class method path which returns the file location of our repository as well as the method createDB. Then we create the repository by executing ToDoDB createDB.

ToDoDB class>>path
^ 'todo'
ToDoDB class>>createDB
MagmaRepositoryController
create: self path
root: ToDoList new.

We define an accessor method for the session and we define a MagmaSession using the path specified before and connect to the session using the method connectAs:. Note here that we send the message MagmaSession class>>openLocal: to the session since we are in local mode.

ToDoDB>>session
^ session
ToDoDB>>connect
session := (MagmaSession openLocal: self class path)
connectAs: 'user'

We make sure that the session will be correctly set in the singleton method by sending the instance message connect we previously defined.

ToDoDB class>>uniqueInstance
^ Default ifNil: [ Default := self new connect; yourself ]

We also define the method release which disconnects and closes the session. Note that the method MagmaSession>>disconnectAndClose deals with the fact that we are in local or remote mode.

ToDoDB class>>release
Default isNil ifFalse: [
Default session disconnectAndClose.
Default := nil ]

The following root method illustrates how we could access the session root object.

ToDoDB class>>root
^ self uniqueInstance session root

We finally provide a class method to commit changes to the database using the method MagmaSession>>commit:.

ToDoDB class>>commit: aBlock
self uniqueInstance session commit: aBlock

Now we are ready to test. We will create a repository, add an item to the list and commit the changes and release the connection.

ToDoDB createDB.
ToDoDB commit: [ ToDoDB root add: ToDoItem new ].
ToDoDB release.

Now using these messages we can decide when we will store the data. For example we modify the method ToDoListView>>edit: and wrap the change of the current item into a commit: so that the resulting objects get stored.

ToDoListView>>edit: anItem
| result |
result := self call: (ToDoItemView new model: anItem copy).
result isNil ifFalse: [
ToDoDB commit: [
self model items replaceAll: anItem with: result ] ]

Magma will detect the changes from the root object and save them if we wrap the action inside commit:.

Note that the Magma tutorial available at http://wiki.squeak.org/squeak/2689 proposes ways to avoid modifying the domain objects to make them persistent.

Copyright © 20 November 2017 Stéphane Ducasse, Lukas Renggli, C. David Shaffer, Rick Zaccone
This book is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 license.

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