How best to add/remove selections

Question

I have an interface where a user is able to click on several choices in a checkbox. Each selection is stored as a separate row in a data table that is linked to their user data. Adding new choices is easy as you just write a new row for that box. Removing them is a bit more tricky. Is there a standard best practice for this row addition/subtraction process?

Mathieu Drouin · Answer

Here is an simple example using local variables: 
 a!localVariables(
 local!checkBoxesFromDB: {
 a!map(id: 1, value: "ITEM_1"),
 a!map(id: 2, value: "ITEM_2")
 },
 local!checkBoxValue: local!checkBoxesFromDB.value,
 local!checkBoxesToAdd,
 local!checkBoxesToRemove,
 {
 a!checkboxField(
 label: "Check box field",
 choiceLabels: { "Item 1", "Item 2", "Item 3" },
 choiceValues: { "ITEM_1", "ITEM_2", "ITEM_3" },
 value: local!checkBoxValue,
 saveInto: {
 local!checkBoxValue,
 a!save(
 local!checkBoxesToAdd,
 a!forEach(
 items: local!checkBoxValue,
 expression: a!map(id: fv!index, value: fv!item)
 )
 ),
 a!save(
 local!checkBoxesToRemove,
 difference(
 cast(
 typeof({ a!map() }),
 local!checkBoxesFromDB
 ),
 cast(
 typeof({ a!map() }),
 local!checkBoxesToAdd
 )
 )
 )
 }
 )
 }
)

Mike Schmitt · Answer

The "best practice" (IMHO) is to not remove but instead deactivate rows that a user un-selects in this manner (via an "active flag" row or a "removed flag" row, both the same thing except for being opposite in value). The question then becomes, what happens if a user re-selects previously un-selected rows? The code is a little trickier but it helps prevent DB rows from getting spammed if you implement a system that looks up any deactivated rows for the current user and marks them as re-activated if they're re-selected (instead of selected for the first time). IMHO it's worth the time and hassle to implement.