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.
Related
I've set up a very simple (Universal Windows) App in C++/WinRT.
It's just App <- MainPage <- DataViewModel <- Data for now.
MainPage has some Sliders etc. which are bound (x:Bind) to DataViewModel, which contains an instance of Data. Working fine so far.
However, the Data is a member of DataViewModel. This seems to be an obvious code smell. Data should not be "owned" by the GUI. All Examples/Samples I've come across seem to be set up like this, though.
I also want to run a background thread (pure C++ code) that works with one and the same instance of Data.
The question: Who "owns" Data. How do I connect things? How to pass the reference?
My best idea so far: The App class itself should just own the one instance of Data. The MainPage ctor should take a Data& and pass it on to the ctor of DataViewModel. However, I don't seem to be able to write a custom ctor for MainPage, because there's generated code involved.
Just pointing me to well coded Sample App would also be appreciated.
IInspectable (in the comment above) makes a noteworthy point: "Ownership really only matters when non-static lifetimes are involved. If Data represents data with static lifetime then there's nothing inherently wrong with exposing it through a static App class member."
In this vein, don't limit your thinking of Data (i.e., the model) to just object(s) which some other object owns. The model should be thought of as a wholly independent component.
Let me approach this notion from another angle. Most people will readily describe MVVM as three independent "layers" or "components" or what have you, wherein the model "doesn't care" about the view model, which in turn "doesn't care" about the view.** In code (as you have seen yourself), you're probably going to find some clear cut ownership patterns to reflect that basic premise. For example, if we're following the the "view-first" approach like the Microsoft samples, you'll start with your App object, which owns an instance of a view object, which in turn instantiates a view model instance.
But the key to MVVM is not who owns whom, it's the relationships between those layers. If you wanted to, you could write a program where, say, the views and view models were all static members of the App class and still have a (conceptually) textbook MVVM structure once everything is hooked up. From that perspective, it doesn't matter where ownership resides.
Now, the thing about Microsoft samples like the Photo Editor is that ultimately they're just demonstrations of how things can work, not a treatise on design patterns. Consider when your data is coming from a database or a web service. Where do you draw the conceptual line between model and view model? The question may sound pedantic, but the way you evaluate these things influences your design decisions.
Which brings me back to your specific question. If it seems like code smell to you when examples you find online stick the model data any old place, you're not wrong. In "real life," the model can be an entire API, not just one illustrative class. You'll potentially have an elaborate subsystem delivering data to you that depends on services completely separate from your application. Or it might be an opaque third-party API that you're calling into via global functions, etc. Just remember that the key isn't "ownership," it's (the conceptual) "relationship." ***
** As a side note, you mention Data being a member of DataViewModel and describe this as Data being "'owned' by the GUI." Ideally, the view model should have no inherent ties to the UI, just application logic. Don't think of it as an extension of UI functionality.
*** But please don't take this post to imply that the actual implementation of the MVVM paradigm isn't important. That's true of any design pattern. The exact form that implementation takes depends on the specific application and whatever your boss wants you to do. All I'm saying is, don't get hung up on ownership. :)
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.
I am looking for an easy-to-implement solution for form-based ontology editing and I wonder if there are any active projects and which of them is the right path to follow.
I need to create instances of an ontology (lets call it ontology A) using forms (either web or desktop) and store them in a triple store (e.g. Virtuoso). I would like to hide as much details as possible regarding the ontological relationships between the entities defined in ontology A and provide a plain simple user interface for CRUD (Create-Retrieve-Update-Delete) operations based on the entity schema defined in ontology A.
For example, I have found two possible solutions in the protege ecosystem:
PropertyFormPortlet It is not a live feature in the current webprotege version.
facsimile project
As described in the respective paper this is a solution that has been implemented for a specific context. Therefore, adapting it to another domain would not be as straightforward as I would like.
I wonder, is there another solution (even out of the protege ecosystem) that could facilitate such a form-based ontology editing. Could somebody provide some guidance?
Just in case someone lands in this question, I write down my conclusions. Practically, none of which I tried worked, but still I found out some interesting things.
OpenLink Structured Data Editor:
OSDE is a browser plugin which aims at populating RDF graphs in the form of files, based on Linked Vocabularies. In my case it didn't work as my locally hosted ontology cannot play the role of a "Linked Vocabulary". However, OpenLink team said they will work on it.
OData2SPARQL:
In our test, the WebIDE did not manage to create the forms out of the box as suggested by the respective video tutorial. However, we managed to use OpenUI library as a client of the OData services automatically created by OData2SPARQL, providing a web service interface for our ontology.
Ontowiki:
In our test environment, OntoWiki partially worked. We could save data but there were some bugs when trying to add properties etc. OntoWiki developers said that they plan to refactor in order to actively support it in newer hosting settings, but this is not the case right now.
[Pre]
I have to say that I'm dummy newbie who is trying to get together important puzzles with such crucial details as DDD, TDD, MVVM, and EFCore. I have an about 10 years of windows form develop experience in complete wrong manner, and after I'm joined to Plurasight I'm understood that I'm just lost my last 10 years, and this is really sad :).
[Problem description]
I have an App that i want to re-write from scratch by using latest and greatest technics that've learned for the last 6 month on Pluralsight, but the problem is that these new knowledge’s is stopping me, because simply I'm afraid that I'll do it wrong again...(that is stupid I know, but it is what it is).
So back to my questions, I have a big problem domain, and pretty well documented business logic, which i have to turn in to the code. I'm understand that my start point is design data layer, for these purposes I want to use Entity framework core (I saw Julie Lerman's course on Pluralsight and I think's she is amazing and inspires me to use EFCore as ORM for my app). But at the same time leakage of experience produces more questions than what I’ve learned with Pluralsight, and I will try to write them all(please don’t judge me too hard)
It is looks like that I will need 2 or even more data model projects in my solution, and here is why I have multiple document set types, each of the type contain more than one reference books used to generate unique file names and data sheets. But it looks weird to me have 3 Data model projects such as MyApp.PackType1.DataModel, MyApp.PackType2.DataModel, and each of them will be preinstalled with the EFCore, and each of them will generates its own database based on Data Context defined by EF. Isn’t it very redundant or this is correct way?
I don’t understand how to join these multiple Data Models projects, including Shared Kernel into the one nice model
I don’t understand what is the best way to design my data classes? Should they be just POCO’s or I can design them as nice looking classes with the private var’s and public properties? What are the best practices in here?
Also I don’t understand what is the best practice to use a MVVM pattern on top of that, and is it applicable at all to use MVVM in this case?
Should I keep my Tests in separate projects like MyApp.PackType1.DataModel.Tests, or keep them in same project?
Best regards,
Maks!
P.S.
Apologize for unclear definitions and questions, English isn't my native language.
It's very complicated to answer your question because you have asked for a lot of details, but I going to provide a brief answer and I hope it will be helpful.
You can have only one model for your entities (DDD) and create sub model from this model in your end level projects (Web API or UI)
Read point #1
You have to create an Entity Layer project that represents your database and then you can create DTO's for specific scenarios
From my point of view, use Angular but you can use another UI framework such as React or VueJs, but I prefer to use Angular to build UI interfaces and consume .NET Core Web API from client
Create unit tests and integration tests for you Web API projects and as additional feature you can use Db in memory provider for tests
May be this guide is useful: https://www.codeproject.com/Articles/1160586/Entity-Framework-Core-for-Enterprise
Regards
Hm, multiple DbContexts (models) usually come about when you have distinct databases you are using. General rule is one Context = one Database. Exceptions can occur when there are a lot of tables that can be grouped functionally, but there are downsides to that approach.
A DbContext is a repository pattern but for individual tables. Using a Unit of Work pattern and layering with a custom repository provider would allow you to make it "appear" as a single database, hiding the complexity from the front-end.
Your entity descriptions are usually created as straight POCO. You can get creative with different DTOs
In a nutshell, an MVVM pattern goes like this:
Request from UI to a controller
Controller possibly issues multiple calls to Data Layer to gather data
Assemble data in a single ViewModel (everything the page needs)
Return to UI
The beauty of the approach is single roundtrip (request/response) to the UI
Separate Project in my opinion. There are techniques to spoof the database connection using EF so you are not using "live" data.
That CodeProject article will come in handy.
Jeffrey Palermo pioneered the onion architecture, which I have found a good approach.
http://www.headspring.com/jeffrey/onion-architecture-part-4-after-four-years/
However his statement "Inner layers define interfaces. Outer layers implement interfaces" seems to contradict IoC, if my understanding is correct, which states that Consumer define interface and providers implement it, i.e. the control lies with the consumer not the provider.
This principle makes sense to me, since, imagine you are writing a UI, this principle means you can get on with creating your UI without knowing anything about the services you are going to call since you are in charge of defining the interface that exposes all the functionality your will need.
So to that end Jeffreys statement seems a contradiction and confuses me about where to put contract(interface definitions), because it seems to imply that:
Domain Layer
MyEntity
IMyService
Service
MyEntityService : IMyService
Since there is no layer beneath Domain, where do I put IMyEntity. Also it means I cannot create a Presentation project until Domain exists and has defined IMyService.
As I side note, where do I place IMyEntityRepository and MyEntityRepository ? Since service relies on IMyEntityRepository and MyEntityRepository relies on IMyEntity
So, where to begin? :-)
Let’s start with the real role of an IOC. According to Wikipedia,
Inversion Of Control is a programming technique in which object
coupling is bound at run time by an assembler object and is typically
not known at compile time.
In your case, your UI will manipulate services interfaces without knowing the service implementation that will be bound at run time. It’s not up to the consumer to define those service interfaces; they will be defined in the application core of your Onion architecture, but we’ll see that later.
"Inner layers define interfaces. Outer layers implement interfaces", that’s how the Onion Architecture is designed, but do not forget that the outermost layer is the IOC! It’s up to the IOC to bind interfaces with the right implementations at run time!
You’re right saying that your UI won’t work without having at least one implementation available for the interfaces you will manipulate. But in this case, if for any reason you need to build your UI first, consider using a mocking framework!
Your last question is about where you need to place your IMyEntityRepository and MyEntityRepository classes. Well, that’s the easy part ;-) IMyEntityRepository definitely needs to be placed within your Application core. All your entities, service interfaces, repository interfaces and whatever interfaces need to be at the same place. MyEntityRepository implementation should be placed somewhere in your infrastructure layer as his role will be mainly to deal with getting data out of the DB.
Hope that helps!
I have worked with Jeffrey for many years, and I would say that IoC is integral to making Onion Architecture possible. Interfaces for external dependencies are defined in projects with few (if any) dependencies (in other words, projects at the "center" of the onion). Classes that implement those interfaces that depend on external dependencies are located in projects at the edge / on the surface of the onion. IoC containers, then, are needed to "hook up" the class implementations on the edge of the onion to interfaces at the core of the onion at run-time.
We've implemented Onion on my project and it's conceptually pretty simple.
Create a project that contains only interfaces and POCO's, we'll call this Contract for now
Create one or more projects that contains the implementations of your interfaces and all your 3rd party things like NHibernate mappings, we'll call this Implementation(s)
Add a direct reference to Contract from projects that need to use this functionality but don't add a reference to Implementation from these projects
In your composite root (application entry point) projects do two things (1) as part of the build copy the latest version of implementation to a configured location (we use AppSettings for the configuration but there are a lot of options here) (2) have your container scan the configured location for your Implementation Dll(s)
This approach allows you to only rely on Contract and the idea is that you can switch Implementation so if you want to move to Entity Framework or something else in the future you only have to reimplement Implementation using that framework.
We also copy the NHibernate DLLs to the configured scanning location and this allows us to make the architecture defensive so that it is difficult to not follow the it because NHibernate is only available where it should be used.
The interfaces in the onion architecture are the ones that the layer depends on (i.e. consumes), whose implementation indeed is provided by the outer layer.
More specifically, the architecture itself does not say you have to abstract the business logic behind interfaces (which you should probably do anyway, in respect of the dependency inversion principle, but that's another story). What is says is that the dependencies of the layer should be modeled as interfaces so implementations can be provided by the outer layer.
The best example is infrastructure code, and particularly data access. Your business logic needs to load and store data, so it defines an interface that it'll consume. The outer layer will provide an implementation using NHibernate or EF or whatever.
Actually, the low-level layers (from the DIP; i.e. the data access and other commodities) are on the outermost layers of the onion, while the high-level layers (i.e. the business logic) are closer to the center.
See also http://blog.8thlight.com/uncle-bob/2012/08/13/the-clean-architecture.html which replaces the domain, business logic and more business logic terms with entities, use cases and interface adapters which IMO are easier to reason about. The farther you go from the center, the most specific you are to what the user sees and use; the closer to the center the more generic; at the center are those things that are transverse to your enterprise, then the use cases which are specific to your app more don't dictate how they'll be used or in which environment (which DB, which UI, etc.), then you'll make adapters between your use-cases and your technical framework (ASP.NET MVC, WCF, WPF –in a non-web scenario–, EF, NHibernate, etc.)