Model View ViewModel (MVVM) Design
Model View ViewModel (MVVM) is an architectural design based off of the MVC model. You can see my post of MVC HERE, if you are unfamiliar with it.
In MVVM, you have Model objects which are pure (containing all the content of the page) and the view still contains the user interface (which can be web, WPF, etc.). The View can either web or application based and is what the users will use to interact with (UI). View model is the in-between that makes this the MVVM.. it is the model but pull out of model what to display on particular view
A great example of its use is for electronic medical records keeping in a hospital with many employees dealing with one patient. In the database, ALL of the patients' data-- let us say this includes the patient's name, date of birth, address, billing information, insurance, blood pressure, pulse, blood work, medical history, medications, current chief complaint, and physical exam.
At the front desk of an ER, the employee will require the patient's name, date of birth, address, billing information, and insurance. And, the user interface would only allow that employee to see that information (of course in an actual hospital there is a little more to this like room assignments, etc.. But I am simplifying this for the example). Front desk user would have a way to enterPatient and create new ones.
A triage nurse would get the patient's name, blood pressure, pulse, and current chief complaint. It is unlikely they would care about the patient's address and billing info. So, nurse user = updateVitals.. plus how to display that!
A physician would continue the exam and get the patient's info about their name, birth, address, billing, and insurance from what the front desk entered. This is relevant because they need their name (what to call them..?), where they are from, their age, what insurance covers the medication they may prescribe, etc. The physician would also get the blood pressure, pulse, and chief complaint from what the triage nurse entered. Lastly, the physician could get the rest of the medical history, labs, physical exam, and medications from the patient.. and enter those into the system.
There are obviously ore factors into this like the billing / discharge department, lab work, RN's, every technician possible, and other employees to consider. There would be confidentiality to consider. Also what to do if multiple people are in the same patient entering data and whose will be overridden or how to simultaneously take both pieces of data and allow them to be fused in a logical matter. Time stamping and adding signatures could be considered. How does one display labs that are too high/low with a simple "H/L" or a red coloring? There is a lot that goes into an application and makes for constant improvement of these systems. Hence, for why MVVM and other variants of the MVC are important because that way all these changes/updates and even more can be easily implemented in the design in a time and cost effective manner for the programmers.
In MVC, that would all just be in the view. Yes, all of that above. And you would have a "fun" time making separate user interfaces for each type of login. This would lead to a lot of extra work and strife from the designer and developer's side.
The design of MVVM and WPF is to facilitate the separation of view layer development (designer's User Interfaces) from the "code behind." Hence, now the UI developers can worry about designing new and better displays while the developers are able to maintain the application functionality and business logic of the programming. The better separation of layers lets teams work more efficiently to maintain and build new systems.
Remember, it is important to consider your application and user needs and the best way to model it for the long run. Nothing is worse than building a solid brick house on a sinkhole, or a water soluble house on a beach where it rains a lot. ;)
