custom_data_sources.rst

Custom Data Sources

To avoid the need for writing a separate endpoint each time we need different data to process the request, each endpoint can have the data sources defined by a user. For example, if we are using the default endpoint which returns objects using the views, we may add one more data source to display a weather forecast on the page.

Data source is the C# class that implements the IDataSource interface. Endpoints can use the data sources as they (or developer) want. Default endpoint uses them to construct the view model for the views. Let’s write our own simple data source which will return some hardcoded values.

Create the HardcodedValuesDataSource class inside the main web application project and implement the IDataSource interface there (in order to be able to write custom code in your Platformus-based web application, you can’t use Platformus as the compiled executable; use it as the NuGet packages instead, or write your own extension project and then put its compiled DLL file inside the extensions folder):

public class HardcodedValuesDataSource : DataSourceBase
{
  protected override dynamic GetRawData(IRequestHandler requestHandler, DataSource dataSource)
  {
    ExpandoObject viewModel = new ExpandoObject();

    (viewModel as IDictionary<string, dynamic>).Add("Value", "Some hardcoded value from our custom data source.");
    return viewModel;
  }
}

As you can see, we used the DataSourceBase abstract class instead of implementing the IDataSource interface from scratch. It provides useful methods to manipulate the data source parameters (see below).

Please do not confuse the data source entity (the Platformus.Routing.Data.Entities.DataSource class which implements the IEntity interface) and the implementations of the IDataSource interface (real data sources). Entities are used to describe the data sources by the users in the backend. They are simple DTO objects, while the real data sources implement some logic. The data source entity contains the CSharpClassName property, which actually defines which C# class is used as the real data source.

Now, when our data source class is added, navigate to the backend’s Development/Endpoints section, then to the data source list of the Default endpoint, and create one more data source:

Please note, that our new data source C# class is automatically resolved and added to the drop down list. Click the Save button. Data source is created:

All the regular pages now have the HardcodedValues property inside their view models. (It is only because the default endpoint acts in this way, but you can implement the endpoint which will process the data sources in a different way).

Let’s update the RegularPage.cshtml view to display the value from our new data source:

<p>@Model.HardcodedValues.Value</p>

Run the web application and check the output:

Good. Everything works as expected.

Data Source Parameters and Parameter Groups

As well as the endpoints, data sources support parameters and parameter groups. The implementation is absolutely the same, so please just take a look at the one for the endpoints. Also, please take a look at the built-in data sources to see how they use this feature.