Which hook to use to reorder multi-value field values before saving content

Question

I have a multi-value field added to my content type. It is actually a field collection.

The users can add unlimited items to this field, and rearrange the items using Drupal's drag-and-drop utility.

However, I want to add some custom logic to the arrangement of field values according to the content.

Which hook should I use, to modify the arrangement of field values before the node saved into the database.

For example, I have the following structure:

My Content Type
|
|-- Field Collection Field // unlimited values
    |
    |-- Name // Text field
    |-- Surname // Text field
    |-- Company // Select list

Let's say a user created a content with the following values:

• John - Doe - ACME
• Jane - Doe - Ace
• Bob - X - ACME
• Fred - Something - Ace

I want to sort them with a custom logic in a hook, so that they are arranged like that:

• Bob - X - ACME
• John - Doe - ACME
• Fred - Something - Ace
• Jane - Doe - Ace

My question is NOT how to write the logic, BUT which hook to use to modify the arrangements so that I can put my function into it.

Answer 1

I would suggest you hook_node_presave to modify node edit form submitted values before saving it into DB.

Answer 2

Attach a custom validate handler for the element and make sure it will be called first. Then in your validate function you can change the field weight in $form_state.