Error 'Field Integrity Exception' when you update Data Categories via API

This error occurs in Salesforce Knowledge when you attempt to associate a child Data Category with a Knowledge Article that has already been associated to the parent Data Category in the same branch.

Why This Error Occurs

For example, if a parent category named "Products" is already assigned to an Article, attempting to also insert an association to its child category "Laptops" from the same branch will fail. Salesforce Knowledge does not allow an article to be categorized at multiple nodes in the same Data Category branch.

Resolution Steps

1. Identify the parent Data Category currently associated to the article.
2. Delete the parent Data Category association first.
3. Insert only the child Data Category association.