model-view-controller
DESCRIPTION
Model-View-Controller. CS 4720 – Web & Mobile Systems. Abstractions and Tiers. Every system we seem to build we talk about tiers How do we reason about the architecture of a system? How can we communicate how the pieces fit together?. A Two-Tier System. A Two-Tier System?. - PowerPoint PPT PresentationTRANSCRIPT
CS 4720
Model-View-Controller
CS 4720 – Web & Mobile Systems
CS 4720
Abstractions and Tiers• Every system we seem to build we talk about
tiers• How do we reason about the architecture of a
system?• How can we communicate how the pieces fit
together?
2
CS 4720
A Two-Tier System
3
CS 4720
A Two-Tier System?
4
CS 4720
Describing the World• We generally refer to client/server systems as
“two-tier systems”• Why?• What does that communicate?
5
CS 4720
A Three-Tier System• How might a three-tier
system be different than a two tier?
• Do we add a server?• Do we add a client?• What does it mean to have
three tiers?
6
CS 4720
Context Clues• It’s all in what you’re talking about.• If you’re discussion the
overall system, includingthe client, a common view of a three-tier architecture might be this:
7
CS 4720
Context Switch• What if we are talking about just inside our
application?• We assume that the client is there, but it is
somewhat immaterial• How do we define the layers now?
8
CS 4720
Three-Tier Architecture
9
CS 4720
Three-Tier Architecture• We will see this architecture pattern over and
over again in this class– Web development– Web services– Android (basically all mobile…)
• Here we are discussing it in the context of a RESTful web architecture
10
CS 4720
Principles of REST• Remember this one?
– 3. Addressable Resources– Everything has its place and every place has a thing– “Everything is a resource”
• This is actually key to how we go about building a three-tier web application
11
CS 4720
RESTful Tiers• If every resource is a place, and every place is a
resource, how do we define our resources?• We know the URL would look something like:
– http://mysite.com/users/mss2x• Where:
– mysite.com is the domain– users is the “category of resources”– mss2x is a specific instance of the resource
12
CS 4720
RESTful Tiers• What we want the web server / web
application to do is translate this:– http://mysite.com/users/mss2x
• Into effectively a function call that– Identifies what the user is asking for– Loads a particular resource– Displays the pertinent info about that resource
back to the user
13
CS 4720
Model-View-Controller• This is the definition of what MVC is• The MVC pattern maps:
– Identifies what the user is asking for– Loads a particular resource– Displays the pertinent info about that resource
back to the user• To Model, Controller, View (in that order)
14
CS 4720
MVC
15
CS 4720
MVC
16
CS 4720
Controller• The role of the controller is basically traffic cop• It takes the request from the user and (with the
assistance of the server and routing rules) turns it into a method call of sorts
• It finds the appropriate model to load• It finds the appropriate view to load• It returns the whole thing back to the user
17
CS 4720
Model• The model is the representation of the data• This may or may not be directly linked to a
database (but often is in larger apps)• A model is often translated directly into a DB
table, with the columns as its attributes• Think “class definition w/ DB backend”• Often contains relationship rules (a Student has
many Classes, for instance)
18
CS 4720
View• The closest thing to what you’ve been dealing
with so far is the view• It’s effectively an HTML template that will be
populated with the appropriate data from the loaded model
• It often has PHP (or whatever) embedded in it• All UI components go here
19
CS 4720
Putting it all Together• So, if you were building a blog, what might
some of the models be?• What are the resources that should have
addresses to them?• How do they relate to each other?
20
CS 472021
REST and MVC• REST and MVC aren’t directly related, but they
intersect in many, many ways• The idea of “nouns” in the system – of
addressable resources – is a major component of both
• In general, a good MVC system will be RESTful, although a RESTful system does not have to follow MVC.
CS 4720
Example Code• What do some of these things look like?
22