How to populate the Select Component with dynamic data in UI Builder

In this topic, I will share how to populate the Select component with dynamic data. This approach will work for any kind of dynamic data, whether it comes from the database, an external data source, or a collection of data you manage within your application logic. The example I review below works with the database as the data source. Let’s review the page setup.

My page consists of a select component and three input fields marked as read-only. The select component will have a list of countries (coming from the database). When a country is selected in the component, the page will fetch additional information about the country and render it in the input components. Play with the live demo of the app.

Here’s my page layout:

Notice the following detail in the Select component setup:

This is rather important. What it means is that every single item in the select component is represented by two properties: value and label. You can assign your own “names” to these properties if needed, but value and label work for most cases. The label property (or the key to be precise) is used to
display a specific option in the select component. This is what the user will see in the component once the data is rendered. The value key is what will carry the actual value of the selected option. If this is too confusing now, hang on, it will become much clearer once we look into the component initialization below.

Before we go into the logic on the page, here’s the database table we will work with. As you can see it has a collection of countries. The following columns are used in the example:

Back in the UI Builder… my On Page Enter event for the page (the event that is triggered when the page is loaded) has the following logic:

Let’s review it step-by-step:

  1. The first step is to load a collection of Country objects. I use the condition Continent = 'North America' just for the demo purposes, it also helps to keep the number of options fairly low, but it is not critical for the demo:
    UI Builder - ConsoleDemo - Backendless 2022-02-02 17-07-57

  2. Once we have a collection of countries returned by the block shown above, we need to do some filtering of these objects. The filtering block (Map Items in List) is used to transform the collection. If you’re not familiar with list/collection transformation in Codeless, I recommend you watch the List Transformations with Codeless Programming YouTube video.

    What happens here is for every item in the countries collection, we’re given a chance to transform it into something else. The Map Items block works as an iterator. The item variable represents the current item from the input collection. The return connector is responsible to return a “transformed” object. The final result of the Map Items in list block is a complete, transformed collection.

  3. The “transformation” logic is below:

    What we do here is for every item (which is a Country object) we create a new object that has the label and value properties (see the properties in the Create Object block?). The reason these properties are value and label is not a coincidence. In here we’re using the “keys” that the Select block was configured with (we talked about it at the beginning of this article). The label property gets the Name of a Country - this is what the Select block will display. The value property gets the Country’s objectId value.

  4. Finally, once the transformation is completed, and we have a collection of objects in a format that is “friendly” for the Select component, we assign that collection as options for the select component:

As a result of this logic, the Select component can now render the data.

Let’s take a look at the logic of selecting an option in the Select component. Click the Select component and switch to its logic screen:

You will see the Select component has the On Change Event. This is the logic I put in there:

The Changed Value context block (the one in the horizontal bar above the logic) contains the value assigned to the selected option. That is the value we assigned here in the page loading logic:

So we know it will be objectId of the selected country. Knowing the objectId value, we can retrieve the country, which is what we’re doing in the Select’s On Change Event. The selected country object is then placed into Page Data with the property of selectedCountry:
UI Builder - ConsoleDemo - Backendless 2022-02-02 17-35-49

The rest (displaying the values in the input fields) is the magic of data binding in UI Builder. Here’s how I set up the input fields:
UI Builder - ConsoleDemo - Backendless 2022-02-02 17-36-48
And then configure the property the Value Logic data binding property:
UI Builder - ConsoleDemo - Backendless 2022-02-02 17-37-21
where selectedCountry is the name of the property we put into Page Data above and Population is the property in the Country object (the property name maps to the column name).

Hope it all makes sense. if not, post a comment.

Happy Codeless Coding.


1 Like

In case anyone else gets stymied by finding the more obscure blocks, they are found here:

“Set Options to Select” I believe needs to be searched for, as it doesn’t seem to be in the menu area. It’s designator in the search field is: ”ui_system_component__select__set_options”

“Load Table Objects” and “Get Object by ID” are found under “Data API”.
The others are more obvious:
“Create Object” and “Get Property” are in “Objects”
“Map Items to List” is in “Lists”

I’m following this example and the error is

“Cannot set properties of undefined (setting ‘options’)”

Step by step to check the object a looks OK…

Screen Shot 2022-06-15 at 22.16.23

This is the error:

Screen Shot 2022-06-15 at 22.16.41

Thanks, Mario

The error indicates that the logic was setting the options property. The logic you shared doesn’t reference that property name anywhere. It means the error is coming from somewhere else.

Hi Mario,
Did you find the solution to the "Cannot set properties of undefined (setting ‘options’)?
I’m getting the same error.
Paul - Backendless user

Yes, my problem was using “Visibility” in a block where I used the “Select”.

Now it’s not my ideal look of the page but it’s working without using the “Toggle Component Visibility”.

Thanks, Mario