Valknut – View Models

The application utilises view models heavily for all kinds of client-side communication. A page view model is an obvious candidate. But even JSON requests and responses are deserialised into a view model for better server-side manipulation.

Core Hierarchy

The application view model architecture is highly formalised. It follows a strong hierarchy for transmitting the various kinds of data models to the client and back. The base of this entire hierachy is the class FitNet.Web.ViewModels.EntityViewModel. This class exposes the properties Id and Name.

All entity view models which are used to enumerate records, show editable forms or delete rows inherit from EntityViewModel. This offers the structure required to perform common sets of actions on these entities irrespective of their individual types and properties.

Page View Model

This is a generic class that is designed for transmitting data for a standard HTML output. It has a single generic type parameter that has to inherit from the EntityViewModel. This class exposes the properties Title, Permalink and Entity. The type of Entity matches the type of the generic parameter.

All entity controllers can use this class to generate an editor page with a shared set of page properties and layout hosting a form with entity type-specific fields.

DataTables View Models

DataTables is a popular jQuery plugin for rendering grids on the client-side. It supports dynamic retrieval of data, page-wise splitting, record offsets and many other features required for viewing collections.

This library is utilised heavily in Valknut, and as a result, the back-end provides built-in view models for data retrieval and submission directly through DataTables.

The classes required for this feature are listed below.

  • FitNet.Web.ViewModels.DataTables.RequestViewModel
  • FitNet.Web.ViewModels.DataTables.ColumnViewModel
  • FitNet.Web.ViewModels.DataTables.OrderViewModel
  • FitNet.Web.ViewModels.DataTables.SearchViewModel
  • FitNet.Web.ViewModels.DataTables.ResponseViewModel

Request View Models

This is a composite class that organises several other view models into a single instance. When the plugin makes an AJAX request, the request is serialised into this type. It’s native properties are Draw, Start, Length and Error. These properties are required for cache-busting, record navigation and error handling.

The Search property contains an instance of the SearchViewModel, while Columns and Order are collections of type ColumnViewModel and OrderViewModel respectively.

Server-side Processing

An AJAX request from a DataTables instance can be processed on the client-side or on the server. In the former scenario, all data is retrieved in a single network operation and stored in memory on the client. This is convenient and quick for small data sets.

But if your data sets are large or contain an indefinite number of rows, server-side processing is more efficient. For this, the plugin sends some additional information with each request.

  1. Column Data
  2. Column Name
  3. Column Searchable
  4. Column Orderable
  5. Column Search Value
  6. Column Search RegEx
  7. Column to Order By
  8. Direction of Ordering
  9. Record Number to Start At
  10. Length of Data Set
  11. Global Search Value
  12. Global Search RegEx

Column and ordering parameters are an indexed collection. The entire request is URL encoded. An example of the body sent is shown below (with the request split into multiple lines for legibility).


Column View Model

The column fields are deserialised into an instance of this class. Each column has its own instance, and each instance has the properties Data, Name, Searchable, Orderable, Start, Length, as well as a nested instance of the search view model.

The server can utilise these values to perform any additional ordering or filtering on the result data set before dispatching it back to the client.

Order View Model

This is a very simple class consisting of only two properties – Column and Direction. The first is the index of the primary sorting column, and the second is a string containing the value asc or desc.

The server can utilise these properties to sort the data on the server.

Search View Model

This class contains the properties Value and RegEx, which is used to transmit keywords or regular expressions to the server. The data set can be filtered against these parameters before returning it to the client.

Response View Model

In addition to the collection of records, the DataTables instance also requires some additional information such as the current page number. This view model implements properties for these values.

The complete list of properties are Draw, Start, RecordsFiltered, RecordsTotal, Search, Error and Data. The last one is an ICollection instance and contains the rows to be rendered.