Unable to create sales order item

Iam trying to insert a record in the Sales Order Item using python code, While submitting the record, the following record is popped up.
Cannot create a Comment against a child document: Sales Order Item

Thanks in advance

@nandeep why do you want to do that?

You should always save the parent document.

@rmehta I created a child table in sales order doc to show eligible free goods for the ordered items with some logic. and our requirement is as follows:
1.user may change the eligible items quantity or he may changes the free item based on some conditions.
2. After making changes, while submitting the order, I am merging the free goods to sales order item table