When the view model property is bound to the form input field with the ability to change their values, the property must be bound without parentheses. If properties are bound with parentheses, that means that data can only be read from an observable value, and not set. After the input field value changes, the bound observable value, by default, is changed only when control loses focus and native JavaScript onchange event is called.
To force the value to be changed as soon as a user presses the key, binding valueUpdate with one of the available values ('keyup', 'keypress', 'afterkeydown') must be applied. Afterkeydown is the best choice if you want to keep the view model updated in real-time. Two methods are created in this first iteration of your view model. The protected LoadProducts() method is responsible for calling the Get() method on the Repository object and retrieving the list of product objects. The public HandleRequest() method is called from the controller to retrieve the product data. In the future, more logic is added to the HandleRequest() method to perform other functions such as searching, paging, adding, editing, and deleting of product data.
The HandleRequest() method should be the only public method exposed from this view model class. By making all other methods not visible outside the class, your controller only needs to ever call a single method. When using MVVM in WPF, you typically have a view model class for each screen. In MVC, you do the same by having one view model class per page. Of course, there can be exceptions, but this separation keeps your controllers and view model classes small and focused.
The controller's GET method creates an instance of the view model and passes it as the model to the page. The page binds to properties on the view model as HTML input or hidden elements. These bound properties may come from an instance of one of your EF entity classes, or additional properties that are specific to that page. If you have input elements on the page, the POST method in the controller accepts the view model as its parameter and all the bound properties are filled in automatically.
Convenience to create a new instance of a model within a collection. Equivalent to instantiating a model with a hash of attributes, saving the model to the server, and adding the model to the set after being successfully created. If client-side validation failed, the model will be unsaved, with validation errors. In order for this to work, you should set the model property of the collection. The create method can accept either an attributes hash and options to be passed down during model instantiation or an existing, unsaved model object.
Now that you've created the Product entity class and the data layer to get a collection of Product objects, you can build your view model class. So far, you may be thinking, why do I need a view model class? I have everything I need in my Product and my ProductRepository classes. The ProductRepository is passed into the constructor of the ProductViewModel class by the DI service in MVC Core.
A method named HandleRequest() is called on the view model to retrieve the data from the Product table using the Entity Framework, which is implemented in the ProductRepository class. Each row of data in the Product table is represented by the entity class Product . A generic list of Product objects is placed into a Products property of the ProductViewModel. This view model class is used as the model to the Products page to create the HTML table. Many of us have been developing for many years and we've seen technologies come and go. However, the basics of how you create classes with methods and properties hasn't changed.
If you keep any technology-specific objects such as Session, ViewData, TempData, etc., out of your view models, then moving from one technology to another becomes easier. For example, I've had many clients create an MVC application, then decide that they want to create a part of that application in WPF for their data-entry people. I only had to create the UI in WPF and simply reuse the view model classes that had already been tested. Walmart used Backbone.js to create the new version of their mobile web application and created two new frameworks in the process. Thorax provides mixins, inheritable events, as well as model and collection view bindings that integrate directly with Handlebars templates. When returning a JSON response, send down the attributes of the model that have been changed by the server, and need to be updated on the client.
When responding to a "read" request from a collection (Collection#fetch), send down an array of model attribute objects. As you can see in the above code, we have created a list of student objects for an example purpose (in real-life application, you can fetch it from the database). We then pass this list object as a parameter in the View() method. The View() method is defined in the base Controller class, which automatically binds a model object to a view. For this article, you're going to be creating the four projects shown in Figure 1.
This architecture is one that I've found to be flexible, reusable, and testable. The four projects are the MVC Core application, and one class library each for your view model classes, data layer classes, and entity classes. For many of you, the only thing that might be a little different is the addition of the view model classes. The focus of this article is to show how to simplify your controllers and move most of your logic into view model classes. A secondary focus is to illustrate how to build a multi-layered project in Visual Studio Code with .NET Core. The key to MVVM in MVC is moving logic out of the MVC controller and into a view model class that contains properties that you can bind to the user interface.
The controller should only call a method in your view model, and periodically set a property or two prior to calling that method. Normally, properties that don't need to be set as view model properties will be bound to controls on your user interface. To ensure reusability of your view model classes, don't use any ASP.NET objects such as Session, ViewBag, TempData, etc. in your view model. New Rdio was developed from the ground up with a component based framework based on Backbone.js. All of this relies on Backbone's views and models, and all URL routing is handled by Backbone's Router.
When data changes are signaled in realtime, Backbone's Events notify the interested components in the data changes. Backbone forms the core of the new, dynamic, realtime Rdio web and desktop applications. The MVC DI service injects an instance of the ProductRepository and the ProductViewModel classes into the ProductController class.
Two private variables hold each of these instances passed in. When the user navigates to the Product/Products path in the MVC application, the HandleRequest() method is called on the view model. This method loads the products into the Products property in the view model. The view model is then passed to the Products.cshtml page, which you're creating next. This allows you to set the repository object in the POST method of your controller. The other property is a list of Product objects that will be loaded with all the products returned from the table.
Add a model to the collection, firing an "add"event for each model, and an "update" event afterwards. If a model property is defined, you may also pass raw attributes objects and options, and have them be vivified as instances of the model using the provided options. Pass to splice the model into the collection at the specified index. By default save checks validate before setting any attributes but you may also tell set to validate the new attributes by passing as an option. In this in-depth guide we created and deployed a fully tested restaurant menu ordering application called place-my-order with DoneJS. We learned how to set up a DoneJS project, create custom elements and retrieve data from the server.
Then we implemented a unit-tested view-model, ran those tests automatically from the command line and on a continuous integration server. If you want to detect and respond to changes on one object, you'd use observables. If you want to detect and respond to changes of a collection of things, use an observableArray. When new items are added, or when items are removed from array, they automatically appear and disappear in the UI. As mentioned before, the best practice is to create a view model with observable properties for each list item.
Add to Views\Shared folder a new partial page named _StandardViewModelHidden.cshtml. In the view model layer project, rename the Class1.cs file to ProductViewModel.cs and delete all the code within this file. Add the code shown in Listing 4 to create your ProductViewModel class.
You need a parameter-less constructor so MVC can create the class in the POST method of your controller. The other constructor is passed an instance of a ProductRepository class when the ProductViewModel is created by the DI system in MVC Core. Fetch the default set of models for this collection from the server, setting them on the collection when they arrive. The options hash takes success and error callbacks which will both be passed as arguments. When the model data returns from the server, it uses setto merge the fetched models, unless you pass , in which case the collection will be reset.
Delegates to Backbone.syncunder the covers for custom persistence strategies and returns a jqXHR. The server handler for fetch requests should return a JSON array of models. A Model manages an internal table of data attributes, and triggers "change" events when any of its data is modified. Models handle syncing data with a persistence layer — usually a REST API with a backing database.
Design your models as the atomic reusable objects containing all of the helpful functions for manipulating their particular bit of data. Models should be able to be passed around throughout your app, and used anywhere that bit of data is needed. With Backbone, you represent your data as Models, which can be created, validated, destroyed, and saved to the server. Knockout is a fast, extensible and simple JavaScript library designed to work with HTML document elements using a clean underlying view model.
When you run this application first time, as you know we are using Code First Approach and in this database and tables will be created automatically. In this article, you got a taste of how to architect an MVC Core application with multiple projects. Separating your entity, data, and view model classes into separate projects provides you with the most flexibility and helps you focus on each layer as you develop. You also learned how little code you need in your controller. Using a hidden field makes it easy to communicate commands to your view model.
In the next article in this series, you'll learn how to do sorting and paging using the MVVM design pattern. Add a new entity class named ProductSearch to hold the two properties to search for. You're also adding a view model base class that all your view models are going to inherit from. This base class contains, for now, just a single property named EventCommand. A view model class holds this additional state data along with an instance of your entity class .
Later in this article series, you're going to add searching, paging, sorting, and CRUD logic to the product Web page. At that time, you're going to start adding additional properties. The GetView() action method accepts two parameters - customerID and viewName.
These two parameters are passed through an Ajax request. Depending on the viewName parameter either CustomerDetails partial view is returned to the caller or OrderDetails partial view is returned. These two view need model in the form of a Customer object and a List of Order entities respectively. Once model variable is populated the partial view name and the model is passed to the PartialView() method. Here, we used partial views because the HTML output is to be inserted in an existing page through Ajax.
That is all the code that is required to get a cascading dropdown. The jQuery code sets up an event handler that will run whenever the selected item is changed, making an AJAX call that is expecting JSON formatted data. When the AJAX call successfully completes it iterates over the collection of objects building an element for each one and sets the HTML of the dropdown to the new list of items. It would be trivial to replace the code in the repository to retrieve data from a database as well, but I will leave that as an exercise for the reader. Backbone views are almost more convention than they are code — they don't determine anything about your HTML or CSS for you, and can be used with any JavaScript templating library. The general idea is to organize your interface into logical views, backed by models, each of which can be updated independently when the model changes, without having to redraw the page.
Parse is called by Backbone whenever a collection's models are returned by the server, in fetch. The function is passed the raw response object, and should return the array of model attributes to be addedto the collection. The default implementation is a no-op, simply passing through the JSON response.
Override this if you need to work with a preexisting API, or better namespace your responses. Override this property to specify the model class that the collection contains. Not everything in my view model has to be an observable. I can still use it for data binding, I just don't need all the functionality provided by an observable.
One important thing to point out is that I won't be touching the server-side code at all. One goal of my previous article was to expose my application's functionality as raw data -- JSON data, to be precise. By removing the use of partial views (which are data + presentation combined), my options for how I work with the data have increased enormously. But the important point is that because of my architecture, I have options. The place-my-order-api module uses the Feathers NodeJS framework, which in addition to providing a REST API, sends those events in the form of a websocket event like orders created.
To make the order page update in real-time, all we need to do is add listeners for those events to src/models/order.js and in the handler notify the order connection. This 3-part article series presents how to use the Model-View-View-Model design pattern in MVC Core applications. The MVVM approach has long been used in WPF applications but hasn't been as prevalent in MVC or MVC Core applications. This article illustrates how using MVVM in MVC makes your applications even more reusable, testable, and maintainable. You're going to be guided step-by-step building an MVC Core application using the Entity Framework and a view model class to display and search for product data. Adding and removing models one at a time is all well and good, but sometimes you have so many models to change that you'd rather just update the collection in bulk.
Use reset to replace a collection with a new list of models , triggering a single "reset" event on completion, and without triggering any add or remove events on any models. For convenience, within a "reset" event, the list of any previous models is available as options.previousModels. Each model can be a Model instance, an id string or a JS object, any value acceptable as the id argument of collection.get. Fires a "remove" event for each model, and a single "update" event afterwards, unless is passed. The model's index before removal is available to listeners as options.index.
Save a model to your database , by delegating to Backbone.sync. Returns a jqXHR if validation is successful and false otherwise. As with set, you may pass individual keys and values instead of a hash.
