I am new to coding and I was wondering what is the logical way of representing the interconnections between classes of a system, more specifically the GUI class and the system's classes. Let's consider an online ordering system. In addition, let's consider that we need to make an order in this system. So I imagine that there is a GUI ( after logging in ) and there is a button for make order. So this means that the GUI class will be connected directly to the make order class ( if we assume that there is a class that is responsible for making orders )? Or there should be some intermediate class that should be connected to the GUI and controls the logic of the system ( if user choices make order then this control class deals with the make order class, if user choices to track order then this class deals with the track order class and so on )? I am looking for the most efficient way of writing code.
Edit: In many textbooks, they mention three types of classes that deal with this issue which are boundary class ( GUI), controller class and Logical class, but actually I don't know the exact meaning of the controller and the logical classes types.
MVC is one famous pattern used for this specific purpose. MVC stands for model view controller.
View = Classes responsible for the UI.
Model = This is the business domain where all complex business logic lives. OOP is heavily used here.
Controller = This connects the view with the model. Example - a click on the UI needs to be fulfilled by a model and the controller will connect the UI to that model.
Add REST to this mix which will help UI communicate with Model and the make the model agnostic to type of clients being Web, Mobile or even another server. Angular, React etc are heavily used for UI presentation.
You would needs a persistent layer to persist the state of the model and read it back. Example - A database which can save historical order and read them back. JPA and Hibernate are famous tools for this.
You don't need to deal this raw MVC, rather use one of many web frameworks which will take care of boiler plate code for you. Spring MVC is one such framework in Java world. There are equally famous frameworks for python, node, scala etc. This framework will have standard ways to do REST, Persistence, controller etc. So start from this.
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I am trying to Create Class Diagram for my Web Application but i dont know how to Represent Database Connection and REST API in Class diagrams.
P.S. I am Creating Class Diagram by following model view controller pattern.
A class is a class
In your class diagrams, you model classes of your system. And all the classes look alike:
a database connection would be a class like another, that will keep some properties about the database context and offer methods for connecting to and disconnecting from a given database.
a REST API class would be a class (or a set of classes) like any other. If you're the API consumer you would certainly have no properties in these classes (because REST is stateless and properties create a state). You could for example have a method for every service you could invoke.
Conceptually speaking theses classes in your system are proxies for something which is out of your system, and which would invoke the APIs provided by the database and the webservice.
But perhaps you want to model something else ?
If your system offers an API, and you want to show how the API offered to the external world relates to your internal classes, you could be interested in using a composite structure diagram.
If you want to show the different components if your system, especially how these are wired together using an API, you could be interested in the component diagram.
If your question is not so much about the structure of the classes and the deeper internals of your system, but more about showing that some part are on remote servers or in containers, you could even think of deployment diagrams. But these are more about the concrete layout of the operating infrastructure, and to link it to the classes, you'd need the component diagrams first.
I'm building a WPF application using MVVM pattern, and Caliburn.Micro is the framework choice to boost up the development.
Different from a conventional MVVM-based application, I add a business layer (BL) below the ViewModel (VM) layer to handle logic for specific business cases. VM is left with data binding and simple conversion/presentation logic. Below BL is an extra Data Access layer (DAL) that encapsulates the Data model (DM) underneath built with Entity Framework.
I'm pretty new to both WPF, MVVM and, of course, know almost nothing about Caliburn. I have read plenty of questions and answers about the Caliburn usage and now trying to use what I've learnt so far in my application.
My questions are:
Does it sound okay with the above layered architecture?
In the application bootstrapper, is it correct that we can register all services that will later be used (like EventAgreggator (EA), WindowManager or extra security and validation services), and also all the concerned VMs? These should be injected into VM instances via constructors or so (supposed I'll be using SimpleContainer). So from any VM that are properly designed and instantiated, we can have these services ready to be used. If I understand correctly, Caliburn and its IoC maintain a kind of global state so that different VMs can use and share it.
Navigation: I know this topic has been discussed so many times. But just to be sure I'm doing the right way: There'd be a ShellViewModel acting as the main window for the whole application with different VMs (or screens) loaded dynamically. Each VM can inherit either Screen or ViewModelBase or NotifyChangedBase. When I'm in, let's say, VM A and want to switch to VM B. I'd from inside VM A send a message (using EA) to the ShellViewModel, saying that I want to change to B. ShellViewModel receives the message and reloads its CurrentViewModel property. What should be a proper data structure to maintain the list of VMs to be loaded? How can stuffs like Conductor or WindowManger come into the place?
Can/Should Caliburn in one way or another support the access to the database (via EF). Or this access should be exposed to VM and/or BL only?
Thanks a lot!
Different from a conventional MVVM-based application, I add a business layer (BL) below the ViewModel (VM) layer
That's the standard case. ViewModels can't/shouldn't contain business logic which is considered to be part of the Model (Model in MVVM is considered a layer, not an object or data structure) in the MVVM. ViewModel is for presentation logic only.
Yes, as long as your Business (Domain) Layer has no dependency on the DAL (no reference to it's assembly). Repository interfaces should be defined in the Business Layer, their implementations in the Data Access Layer.
Yes, Bootstrapper is where you build your object graph (configuration the IoC container).
Registering ViewModels: Depends on IoC framework. Some frameworks let you resolve unregistered types, as long as they are not abstract or interfaces (i.e. Unity). Not sure about Caliburn, haven't used it. If the IoC supports it, you don't need to register them.
One possible way to do it. I prefer navigation services though, works better for passing around parameters to views and windows that are not yet instantiated and you always know there is exactly one objects handling it.
With messages, there could be 0, 1 or many objects listening to it. Up to you
What do you mean with support access to the database? You can use it to inject your repositories and/or services into your ViewModels, other than that there isn't much DB related stuff to it.
I'm working on a database application that manages industry-specific inputs and then runs that information through somewhat complicated calculations, lookups, etc. to return a series of other values and a go/no-go conclusion.
I've decided to use Entity Framework (code first for provider independence) and WPF (MVVM pattern). I'm using the POCO entities as my data model and the view model is handling the usuals like basic data / business rule validation.
It seems EF + WPF/MVVM are great at displaying and validating input and getting it into the database for querying for your typical business application like a products, customers, orders setup. But it's not at all clear where to plug in a "calculations layer". Between the view models and the data models (my POCOs), things are already feeling a bit bloated, and now I'm facing adding another layer very much like the other two.
Perhaps the best way to approach this is to make the calculations layer a sort of meta-view model and push as much of the validations, change notification, etc. into them and run with lighter actual view models.
Anyone run into a situation like this?
Edit
Turns out what I really needed was to thin the view models and beef up the entities. So I lightened the view models, moved property change notification and basic validation to entities to allow for direct binding, and made calculation classes directly consume entities as well as adding some basic routines to entities. Thanks for the links on thought ADM articles #Peter Porfy.
For moving validation closer to entities, used Fluent Validation (excellent suggestion #Gloopy!). To make it easier to implement property changed notification on entities, adapted this technique. And to avoid having to create endless property wrappers in view model (to set HasChanges property) I used Josh Smith's PropertyObserver.
MVVM stands for Model-View-ViewModel, where the Model layer contains everything what models your actual domain problem.
So it depends on what you mean 'calculation layer'.
Put it where it belongs.
If the actual operation belongs to a domain entity, then you should put that logic into the entity. Don't make anemic domain models:
Article from Martin Fowler about ADM.
DDD works perfectly with EF code-first.
If something doesn't belong to any entity then probably you should expose that as a service. Then use that from your viewmodels through an interface.
A dependency injection container could make your life easier here, but you can live without it.
You aren't plugging another layer because it's the model layer. Your viewmodels should stay as thin as possible, just modelling your view's state and forwarding actual business operations to the entity/service classes.
I'd probably create an interface/object to handle calculations (or several if they can be split up logically) and pass that object in wherever you would want to use it. You might benefit from using a dependency injection framework maybe this post can help with that so you wouldn't have to explicitly instantiate your objects where you need them.
Also this post mentions FluentValidation.NET which may not apply completely but there are likely some good patterns to learn from/use there as well.
I'm about to develop this small website, its basically a simple web app to store informations about patients for a doctor.
The company i have got the assignment from demands an introducton with a class diagram, honstly, i have done this already but only for standalone apps, i'm very new in designing class diagrams for websites.
What i'm using is the Ivar Jacobson's iterative metho with usecases, where a usecase includes:
Actors, scenario (representing user-system interactions when all goes fine), and worse case scenatio (solutions when something goes wrong).
By applying this i came to a good conclusion, a well prepared class diagram.
My problem is that i'm doubting whether or not i should include jsp views and servlets(in my case action beans since i use Stripes) in the diagram, i mean, the bridge between the business-classes and the user are the jsp-views and the provided info are going to be processed by the servlets (or action beans), would you include them in the class diagram?
For a small project tis might be not that relevant but what if you have a project with 30 views and 20 servlets, the diagram would become messy and huge.
Do you have some tips about it?
Thank you
If the only reason you need the class diagram is to satisfy the client, best find out what they're looking for first.
If however they're not specific (and ignoring the cynical options) I'd suggest the following:
Create a "Domain Model" diagram. i.e. capture the concepts in the domain and their inter-relationships. So Doctor, Patients and associated stuff.
Don't create a "design" class diagram - i.e. no jsps, servlets, etc. If necessary create a simple architecture picture instead showing how the application is layered.
Rationale: a domain model is good for checking scope and verifying domain rules (relationships). A "design" class diagram only obfuscates that. A proliferation of jsps, controllers, etc. hides the underlying architecture pattern while distracting from the useful stuff in the domain model.
hth.
Sorry if this is a duplicate, It's not so much 'What is MVVM' though, but rather, 'Is this MVVM', I've read quite a bit, and think I've got a basic understanding of what it is, I've got my own 'one-liner', as such, on how I interpret it, but want to make sure it's correct before I firmly ingrain it in my head,
Essentially; The Model is pure data - no methods, there is one ViewModel per Model, it holds a reference to the Model - it performs all changes to the Models data and finally the View will hold one (or more) ViewModel reference(s) and format & display the data provided by the ViewModel.
(Not after links to tutorials, blogs etc, just a yes, or no with tweaks will be fine, as I'll have to re-read everything again anyway if not :) )
Not completely - at least, not as I would completely define it.
The Model does not have to be pure data. The model is the portion of your application that is completely domain specific, and has no "presentation related" information.
This will typically include all of the domain specific data, but also potentially methods that are pure business logic, and data access, etc. Anything specific to the business logic and processes, and not part of the "display", is part of the model.
Also, although "one ViewModel per Model" is the most common form of working, there are times when you may expose a "model" class through multiple ViewModels. This can be useful, for example, if you are trying to expose only part of a model to your designer, as it allows you to make a smaller ViewModel class. The ViewModel adapts the model for work with the View - if the entire Model is not required, this adapter can be made smaller (and more easily testable, maintainable, etc) by only working with the portion required.
Personally, I prefer to think in terms of "one ViewModel per View", as the ViewModel can adapt one or more models in order to work appropriately with a given View, but even then, sometimes it's helpful to swap out a ViewModel within the same View in order to change content.
Close, but not quite. Here are some points that are are different than yours:
Models can have methods on them. They are not just data. They might have methods like "retrieve", "store", etc. Business logic code. View agnostic.
There is no restriction to how many ViewModels hold a reference to the Model. ViewModels encapsulate view-level behavior, so you may have many different sets of behavior for the same model. For example, one ViewModel might be a read-only transformation of a model item. Another might provide read/write form validation on the same model item.
There can be more than one ViewModel per view, based on the behavior you want. For example, you might include "premium content" behavior with one ViewModel and "free content" behavior with another ViewModel but maintain the same view.
Essentially, yes. Practically, not really. Best practice is always to reduce dependencies and split up your responsibilities among classes on a 1:1 basis, but you'll find IRL situations where it isn't as easy to be a MVC purist.
I think the best attitude is to do your best, then document the rest. Don't sweat purity too much.
There is a lot of great information here, and I think that most of these answers are right. I don't think there is any 1 specific definition, nor is there 1 specific authority on this matter. Even microsoft does not really have clear definition on this.
The one item I would add which is not in the name of MVVM, but is common to all implementations of MVVM that I am familiar with. This is a Messaging or Notification system, which seems to always be linked as a platform for the ViewModel. Messaging just notifies the View Models when things change which may affect others. A good implementation of this in mind allows View Models and Views to both be agnostic about things they do not directly bind to by using generic notification messages.
The benefit of the entire pattern in my opinion is to make you application with modular, swappable parts with as little type-dependency as possible.
This is a real missing part in my mind, as it provides the same benefits / functions that you gain from separate controller logic in the MVC pattern.
That is pretty close. Except it is not correct to say that the Model is only pure data. It can and should contain methods for performing the various use cases against it.
Your understanding is wrong.
You can have several Models and all of them could have their own Views and then be a part of a single ViewModel.
Example:
You have the Models: Product, Customer
Each of them have their own View represented as a Custom Control
And you have a ViewModel which combines all your models and finally on the window of your app you combine all together your Views which talk to your Models via your ViewModel
Think of it like this. The Model is your system, the meat and veg of what the system does. The only considerations it has is how to do it's job, not how it is going to be used. It exposes events, attributes and methods defined at the system level, but it has no concept of what will be pressing it's buttons (or if it even has buttons!). It does not try to format data to a more user friendly format, it formats its data in a model friendly way.
The view model is the UX (user experience). It defines how you are going to use the system. It defines (through public commands and attributes) user orientated access into the system. It is the bridge that the user will use to enter the system. It binds onto the events of the model, and through it's commands, it will provide access into the models functionality.
It should handle validation, (is that age a sensible age?) retrieve data, converting and caching of records whilst they are being displayed. So, for example, you're looking at a patient record, the viewmodel gets the data from the model, and caches it internally, then publishes this to the view. What happens if the model announces an update to that data? Throw the cached data away? what if you've edited it? This is all up to you, and this behavior should be defined in the view model.
The view model is a "contract" of what functionality and data is exposed to the user (through the view). The view model has no concept of HOW it is going to be displayed or interacted with. Commands should be named at a functional level, such as RefreshList, NOT MouseClickHandler.
Finally, the View. This is simply a visible representation of what is in the view model. Buttons and menus etc bind onto commands. Fields bind onto attributes and will update automatically through the magic of binding.
If you ever see yourself doing : "text1.text = value" you're doing it wrong. If you ever find yourself writing a command handler that says "my.ViewModel.SomeCommand" you're doing it wrong.