Tersus: Demo Stage 7 – Categories: Classifying items by (mutually exclusive) categories

Demo Stage 7 – Categories: Classifying items by (mutually exclusive) categoriesDate: Nov 28, 2023Item CategoriesWhen the list of items gets longer, classifying the items becomes helpful. For example, we may want to arrange our shopping list by department in the supermarket.We will add a 'Category' column to the item table and show how we let the user select a category from a list of categories managed in the system.Adding the Category FieldUsing the 'Table Wizard':

In the '<Desktop View>', right click on

'Items' and select Apply Table Wizard.

Add a field 'Category' (Text).

In the 'Valid Values' column of the wizard, list a few categories, separated by commas: "Dairy", "Drinks", "Meat" (quotes are not strictly required unless you have leading or trailing blanks).

Press 'Finish'.

The wizard will update your model with the additional field in all relevant places. If you now save your model and restart the application, you will be able to specify a category for any item you choose: Chooser with List of Valid Values

Download Model: Stage 7, Interim Model (version 2.1.9) What Has happened Behind The Scenes?The wizard has used the mechanism of user defined data types with valid values, and then created a Chooser field using the user defined data type. If you start the application, you will see that the Category field is represented by a drop-down list that lets the user choose one of the 3 values we have specified (Dairy, Drinks or Meat).Click here to read more on valid values and user defined data types. Managing a Table of CategoriesSpecifying the list of valid values explicitly in the Table Wizard is probably good enough for our simple Shopping List application, but we may want to give the users the ability to manage the list of categories.This can be achieved by creating a table of categories and specifying that the 'Category' field in 'Items' will refer to this table (i.e. specify the valid values through a foreign key that references the table of categories).Here are the steps to create and use a table of categories:

In the '<Desktop View>', add a row above

'Items' (drag 'Row' from the 'Display' section of the palette). Name it 'Top Row'.

Drag into 'Top Row' a label (also from the 'Display' section of the palette). Name it 'Categories'.

Make the 'Categories' label a hyperlink that opens a dialog for managing the table of categories:

Drag into 'Categories' an action (from the 'Basic' section of the palette).Name it '<On Click>'.
Drag into '<On Click>' a dialog (from the 'Display' section of the palette). Name it 'Categories' or 'Manage Categories'.

Drag 'Table Wizard' from the 'Display' section of the palette into the dialog:

Set 'Display Name' to 'Categories';
Add a field 'Name' (Text) [primary key of type 'User Input'];
Add additional fields, if you like;
Uncheck 'Show paging header group';
Press 'Finish'.

In the 'Footer' of the dialog, delete the 'OK' button and rename the 'Cancel' button to 'Close'.

Save the model, stop the application, and then re-launch it (

). You should see a Categories link at the top of the screen, and pressing it you will be able to add categories to the table of categories. Add a few categories (e.g. Dairy, Drinks, Fish, Meat, Fruit and Vegetables).
Managing Categories

Note that since 'Name' is the primary key of the 'Categories' table, once you create a category, you cannot change its name (only update its 'Comments' field or delete it).

Now that we have a table of categories, we can refer to this table instead of specifiying the list of categories explicitly in the model:

In the '<Desktop View>', right click on 'Items' and select Apply Table Wizard.
In the valid values column of the 'Category' field, erase the listed values and instead write Table=Categories, Column=Name.
Press 'Finish'.

Save the model. If you now stop and restart the application, you will see that when you create a new item, the 'Category' drop-down presents all the categories you have created.

Temporary workaround: There is currently a bug in the order of initializations in <Mobile View>, and an early initialization process <Init> causes mistakes. On the other hand, the initialization is required to get the valid values for the 'Category' field in <Mobile View> as well. To bypass the bug:

In '<Mobile View>', select '<Init>', press Copy, zoom into 'Shopping List/Content', and press Paste (Clone) [not Paste (Reuse)].
In the new copy of '<Init>' , add an ancestor reference to '<Mobile View>', delete the exit 'Valid Values', and make the flow go to the '<Valid Values>' element of '<Mobile View>'.
Back to '<Mobile View>', rename '<Init>' to '<Don't Run>'. <Don't Run>, like <Init>, is recognized by the Table Wizard, and will be updated when table definitions are updated.
Save the model and restart the application.

Sorting by CategoriesThe user can easily sort the table of items by categories.After launching the application, click the 'Category' column title to sort the items in ascending order of their categories (indicated by a small up-pointing rectangle at the column title).A second click on the 'Category' title will reverse the sort order (note that the small rectangle at the column title is now pointing down). A third click disables the sort.Sorting can be made by any other field as well. Since the Table Wizard contains a built-in sorting mechanism, you can click the title of any column in the table. You can sort the table by one column or several columns.Download Model: Stage 7, Final Model (version 2.1.9)Try It Online Next: Controlling which items to showSee Also:

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