How to update a computed field in a rule's "set data a value" action

Question

I have a custom field called field_balance in the user account form which is a computed field. It keeps the actual number of coins bought by the current user. That value is supposed to change (increase or decrease) if the user makes particular manipulations on my custom content type which is called Ads.

How do I increase the field's value? By setting up the field.

How do I decrease the value? I am using Rules module to make the field's value decrease. But it doesn't work well yet. This is what I have already tried:

• The Event: After updating existing content of type Ads
• The conditions: User has roles "ad editor"
• The Action : Set a data value. But when I select the field called "site:current-user:field-balance" and hit "Continue", The Data selector turns red and a notification appears.

Here is the illustration:

What is it about the computed field that does not continue the rule? Is there any other way to update a computed field with the Rules module?

Answer 1

I cannot answer your question directly, so I will propose a solution without computed fields for your specific situation. Since your computed field is just a sum of two other fields, it is perhaps easier to replace it with an ordinary integer field Balance and update its value with a simple Rule every time the entity in question changes. In order to allow users to see the field Balance, but deny them access to edit it, you can use the Field Permissions module:

The Field Permissions module allows site administrators to set field-level permissions to edit, view and create fields on any entity.