Denormalize Data to Improve Performance

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1 Introduction

This how-to explains how you can improve performance by de-normalizing data in Mendix.

This how-to will teach you how to do the following:

  • Denormalize data
  • Keep denormalized data in sync

2 Prerequisites

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

3 Denormalization

Let’s assume that the domain model contains two related entities called Customer and Order. The customer overview page needs to show the name of the customer and the total order amount next to each other. Showing the customer name is easy, but the total order amount needs to be calculated.

To show the total order amount, there are two options:

  • First option: create a calculated attribute in the Customer entity to compute the total order amount (the downside of this option is that the calculated attributes bring down the performance of overview pages)
  • Second option: create a persistent attribute in the Customer entity that stores the total order amount in the database – this is called denormalization (the downside of this option is that the redundant data needs to be kept in sync, but this is easy with Mendix event handlers)

To enable denormalization, follow these steps:

  1. Create a domain model that looks like this:

  2. Double-click the Customer entity to open the properties editor:

  3. Add a currency attribute TotalOrderAmount.

  4. Create an overview and detail page for the Customer entity.

  5. Make sure the customer overview page shows the TotalOrderAmount value.

  6. Make sure the order detail page has a mandatory reference selector to select the customer.

Now the application is ready to store redundant data, but you still need to keep the data in sync.

4 Keep Denormalized Data in Sync with an After Commit Event

  1. Open the domain model and double-click the Order entity to open its properties editor.
  2. On the Event handlers tab, click New to add a new event handler:

  3. On the New Event Handler pop-up window, do the following:

    • Select After as the Moment
    • Select Commit as the Event
    • Select Yes for Pass the event object
    • Click Select… to open the microflow selector

  4. On the microflow selector, click New and enter a name for the new microflow (for example, Order_AfterCommit).

  5. Click OK to create the new microflow, and then click OK again to save the event handler.

  6. Open the new microflow, which should look like this:

    Let’s take a moment to think about what the new microflow should do. We want to calculate the total order amount and store this value in the customer object. As you can see, the current microflow only has an order object as an input parameter. So, first we need to retrieve the corresponding customer. Then we need to get all the orders of this customer and calculate the total order amount. As soon as we have the total order amount, we need to store it in the customer object. Once you’re done, the microflow should look like this:

  7. Open the Toolbox, which should be docked in the bottom-right corner of the Modeler. If you can’t find the Toolbox there, you can open it from the View menu:

  8. Drag a Retrieve activity from the toolbox to the line between the start and end event on the microflow, which will insert a new retrieve activity:

  9. Double-click the new activity to open its properties on the Retrieve Objects dialog box and do the following:

    • Select By association as Source
    • Click Select… to open the Association selector

  10. On the Select association pop-up window, select Order_Customer from the Variables node in the tree view, and then click Select:

    As you can see below, the Output section of the Retrieve Objects dialog box is configured automatically:

  11. Click OK to save the activity. Your microflow should now look like this:

  12. Insert another retrieve activity (as you did in step #8), double-click it to open its properties on the Retrieve Objects dialog box, and do the following:

    • Select From Database as Source
    • Click Select… to open the entity selector

  13. On the Select entity pop-up window, select Order via from the Variables node in the tree view, and then click Select:

    As you can see below, the XPath constraint and Output sections of the Retrieve Objects dialog box are configured automatically:

  14. Click OK to save the activity. Your microflow should now look like this:

  15. Insert an aggregate list activity, double-click it to open its properties on the Aggregate List dialog box, and do the following:

    • Select OrderList as the Input Variable
    • Select Sum as the Function
    • Select TotalPrice as the Attribute
    • Enter SumTotalPrice as the Output Variable name

  16. Click OK to save the activity. Your microflow should now look like this:

  17. Insert a change activity, double-click it to open its properties on the Change Object dialog box, and do the following:

    • Select Customer as the Input Variable
    • Select Yes as the Commit action
    • Select Yes to refresh in the client (the object changes are made on the server side, and with this option, the server triggers the client to refresh the object)
    • Click New to create a new change item
  18. In the Edit Change Item dialog box, do the following:

    • Select TotalOrderAmount as the Member
    • Fill in $SumTotalPrice as the Value
    • Click OK to save the change item

  19. Click OK again to save the activity. Your microflow should now look like this:

  20. Run the application and create some customers and orders. You should now see an up-to-date value for the TotalOrderAmount.