2. Concept

The concept is a special kind of type. The values of a concept are not known within the context of a widget. However, if you create a generic widget, you don't need to know them. Let’s take a look at the following WEMscript to illustrate this.

Throughout the examples, we will assume we have a concept data model property called ConceptProperty.

var @c: concept

/* Assign @c with the concept value that is inside the property @ConceptProperty */
@c := @ConceptProperty

/* This will throw an error: 'Colors'.'Red' is an unknown concept in the context of a widget */
@c := 'Colors'.'Red'

/* Executing concept-specific functions is allowed */
var @d := Description(@Color)
var @s := ToString(@Color)
var @i := ConceptId(@ConceptProperty)

Notice that everything works except for the assignment of the 'Colors'.'Red' concept literal, which is unknown in the context of a widget and only recognized within a project. To assign a concept data model property a new value, we use arbitrary IDs by calling the ConceptId() function. Fortunately, these IDs are just integers and can be easily passed around in the code.

Now, let’s look at the following dropdown example widget that uses a range of concepts to set the @ConceptProperty:

Dropdown Concept Selector

<? register input @ConceptProperty ?>
<select name="<?attr OutputId(@ConceptProperty) ?>">
<? loop range of @ConceptProperty ?>
	<option value="<?attr ConceptId(concept) ?>" <? if concept = @ConceptProperty ?>selected<? end ?>>
		<?= concept ?>
	</option>
<? end ?>
</select>

In the above example, we have created a writable concept data model property called @ConceptProperty. The context of this concept is unknown to us; it could represent a range of colors, animals, or the status of a ticket. However, in this case, we do not need to know the specific context. We obtain the range of @ConceptProperty using the range of keyword and enumerate through it with the loop. We create the <option> elements where the values are generated using the ConceptId(concept) function, with concept being a special keyword that refers to the current enumerated concept within the range of @ConceptProperty. By comparing concept with @ConceptProperty, we can determine if the latter holds the value of concept, allowing us to select the appropriate option.