I'm trying to set a default value when my attribute comes up null in the database:
case categories.rental_price_percentage when null then '15.0' else categories.rental_price_percentage end rental
However, the replacement value isn't taking hold when I hit a null value (the rest is working though), it only displays null:
{
id: "3",
category_name: "Chairs",
rental: null
}
How can I get the default value in and working?
WHEN NULL in a simple CASE expression (it's not a statement) will never match because that would require, in your case, categories.rental_price_percentage = NULL to be true. But the result of comparison operations like =, >, ... against NULLs are NULL i.e. not true -- on only one or both sides, so even NULL = NULL is not true.
To check if an expression evaluates to NULL IS NULL is used.
So you could use a searched CASE expression:
CASE
WHEN categories.rental_price_percentage IS NULL THEN
15.0
ELSE
categories.rental_price_percentage
END rental
But replacing NULLs is such a common task, that there exists a function to do that, coalesce(). It returns the first of the arguments it gets passed, that is not NULL.
So in your case you could simply use:
coalesce(categories.rental_price_percentage, 15.0) rental
Note that I also removed the single quotes around 15.0 as it's presumably meant as a numeric value, not a string.
else set up because the user is able to change the value from default; for instance, I could set it to 50% in the settings, and the value will render fine.
coalesce() call too.CASE expression, you can do the same with the coalesce(). Unless there's probably an ActiveRecord way of doing this. But that would be another question then.