Server-Side Paging and Sorting for a Microflow Data Source

Last modified: August 27, 2024

Introduction

Using server-side paging and sorting for a microflow data source, you can model out how you retrieve data to a single page and ensure it ends up in the correct sorting order. With this approach, you do not need to return all the data to the client — you can just return a single page. This can be helpful for getting data from external sources like a REST service, but can also be useful for a regular retrieve activity in a microflow. To do this, however, you must model the logic for getting the correct data in the microflow itself.

This how-to teaches you how to do the following:

  • Create a data grid with a microflow data source which retrieves data from a REST service
  • Add server-side paging and sorting to that data grid

Prerequisites

Before starting this how-to, make sure you have completed the following prerequisites:

Creating a Microflow Data Source

In this section, you will create a JSON structure and import mapping for a REST service. To do this, complete the first four sections of Consume a REST Service — (until Adding an Input Entity to the Domain Model is done).

You must complete these steps with one crucial change: you must use this REST service URL for your JSON snippet: https://my-json-server.typicode.com/mendix/howto-api-data/airports.

Once successful, your app should have the following elements:

  • A JSON structure based on the airport data:

    json structure

  • Import mapping:

    import mapping

  • An input entity added to the domain model:

    input entity

Now, you can start calling the REST service from your microflow data source. To create a microflow data source which returns a list of characters, do the following:

  1. Right-click your module, click Add Microflow, and create a new microflow named Call_REST.

  2. From the Toolbox, drag a Call REST service activity into the microflow.

  3. Double-click your Call REST service activity.

  4. Click the Location > Edit button:

    edit call rest

  5. In the Template field, add https://my-json-server.typicode.com/mendix/howto-api-data/airports and click OK:

    airport template

  6. Click the Response tab:

    response tab

  7. Select Apply import mapping from the Response handling drop-down menu.

  8. Click Mapping > Select and select the import mapping you created.

  9. For Variable Name, type Result. Click OK to accept the changes:

    variable result

  10. From the Toolbox, drag the Retrieve activity into the microflow and double-click it.

  11. Click Association > Select, click Expand All, and select JsonObject_Summary (List of NativeMobile.JsonObject).

  12. Click OK to accept this association.

  13. Right-click the Retrieve activity and select Set $JsonObjectList as return value:

    set return value

Creating a Data Grid with a Microflow Data Source

In the previous section, you created a microflow which returns a list of characters. Now, you will use this microflow as a data source for a data grid:

  1. From the Toolbox, drag a Data grid onto a page.

  2. Double-click the blue header of the newly-placed data grid.

  3. Click the Data source tab:

    data source tab

  4. Select Type > Microflow.

  5. Click Microflow > Select and select the Call_REST microflow.

  6. Click OK to accept the changes to the data source.

  7. When you see the “Do you want to automatically fill the contents of the data grid?” pop-up window, click Yes:

    click yes

  8. When you see the “Do you want to generate controls for microflow source parameters of the data grid? This will enable server-side paging sorting and searching for the grid.” pop-up window, click Yes:

    click yes again

This generates a data view around your data grid, creates the necessary widgets and nanoflows, and adds the Paging object as an input to your microflow:

paging object

Adding Paging Support to the Microflow Data Source

In the previous section, you added the Paging input parameter to your microflow. This parameter contains the PageNumber attribute which is updated when you navigate through the pages with the paging bar in the client. In this section, you will use the PageNumber attribute to retrieve a specified page from your REST service:

  1. Open the CallREST microflow.

  2. Double-click the Call REST service activity.

  3. Click Location > Edit.

  4. Change Template to https://my-json-server.typicode.com/mendix/howto-api-data/airports?_limit=5&_page={1}:

    add page bit to template

  5. Click Parameters > New for a new parameter and enter the following expression toString($Paging/PageNumber) for this parameter:

    add page number parameter

  6. Click OK to accept this expression.

  7. Click OK to accept the changes for the location, and click OK once more to accept the changes for the Call REST service activity. You are now back at your microflow.

Deploy your app and navigate to the page where you added your data grid. You can now use your newly added server-side paging by using the paging bar buttons above the data grid.

Adding Server-Side Sorting Support to the Microflow Data Source

Now, you have service-side paging for your data grid. Next, add server-side sorting to it.

Clicking the header on the data grid in the client will update the Paging entity by setting the attribute SortAttribute to the attribute which is associated to the header you clicked, and the SortAscending is set to true for ascending and false for a descending sort order.

Use these attributes when calling your REST service:

  1. Open your Call_REST microflow.

  2. Double-click the Call REST service activity.

  3. Click Location > Edit.

  4. Add &_sort={2}&_order={3} to the end of your current Template address:

    add sort and order bits to template

  5. Click Parameters > New to add the second parameter and enter the following expression toLowerCase($Paging/SortAttribute):

    add second parameter

  6. Click OK to accept this expression.

  7. Click Parameters > New to add the third parameter and enter the following expression if $Paging/SortAscending then 'asc' else 'desc':

    add third parameter

  8. Click OK to accept this expression.

  9. Click OK to accept the changes in the location.

  10. Click OK once more to accept the changes in the Call REST service activity.

Deploy your app again and navigate to the page with your data grid. Click the column headers to see your server-side sorting in action!

click headers to sort

Setting a Default Sort Order

You can set a default sort order for data. When a user has not clicked a header, the data will be ordered in the default sort order:

  1. Open the page containing your data grid.

  2. Right-click the data view surrounding the data grid.

  3. Select Go to data source nanoflow.

  4. Double-click the Create object activity:

    create object activity one

  5. Click New to set the value for a member of the Paging entity.

  6. Click the Member drop-down menu and select SortAttribute (String (200)).

  7. Set Value to 'Name':

    name value

  8. Click OK to accept the changes to the member, and click OK once more to accept the changes to the Create object activity.

Deploy your app again and navigate to the page with your data grid. The data is now ordered by Name.

sorted by name

Disabling Server-Side Sorting

Apps that use a REST service which does not support sorting, or apps which do not enable users to change sorting order, require special functionality. In these cases, disable sorting so that clicking the header has no effect:

  1. Open the page containing the data grid.

  2. Right-click the data view surrounding the data grid and select Go to data source nanoflow.

  3. Double-click the Create object activity.

  4. Click New to set the value for another member of the Paging entity.

  5. Select Member > IsSortable (Boolean) from the drop-down menu.

  6. Type false into Value:

    value false

  7. Click OK to accept the changes to the member, and click OK once more to accept the changes to the Create object activity.

Deploy your app again and navigate to the page with your data grid. The data is still now ordered by Name, but you can no longer change the sorting by clicking the header. Note the lack of an arrow above the Name header.

sorted but not clickable

Adding Server-Side Searching

Generating controls also generates input fields for all your attributes of the entity the microflow returns. These inputs can be used by your user to enter search criteria, which can be used to filter the data set on the server. Any data entered in the input fields by the user is set in the Paging entity which is passed to the data source microflow.

You only need to use this data in your microflow and pass the search criteria to your REST call to get a filtered set of data. As an example, follow the instructions below to filter the Name attribute:

  1. Open your Call_REST microflow.

  2. Double-click the Call REST service activity.

  3. Click Location > Edit.

  4. Add &name_like={4} to the end of your current Template address:

    add search bits to template

  5. Click Parameters > New to add the fourth parameter and enter the following expression:

    if $Paging/Name = empty then '' else $Paging/Name
    add fourth parameter

  6. Click OK to accept this expression.

  7. Click OK to accept the changes in the location.

  8. Click OK once more to accept the changes in the Call REST service activity.

Deploy your app again and navigate to the page with your data grid. Enter a value for a part of the name, for example, International, and click Search to see your server-side searching in action!

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