I like the way Django Postgres Extras handles it, but I believe copying that functionality would require some mayor rewriting of how Django Postgres Copy works.

A very rudimentary solution I propose is passing a list with the following order:

Operation (DO NOTHING or DO UPDATE)
Constraint (the name of the column with a constraint)
Columns to update (in the case of DO UPDATE)

I replaced ignore_conflicts with on_conflict and defaults to an empty list:

def __init__(
    ...
    on_conflict=[],
    ...
):

def insert_suffix(self):
    # If on_conflict is not an empty list
    if self.on_conflict:
        # First item on list - Operation
        if self.on_conflict[0] == 'DO NOTHING':
            return """
                ON CONFLICT DO NOTHING;
            """
        elif self.on_conflict[0] == 'DO UPDATE':
            # Second item on list - Constraint
            constraint = self.on_conflict[1]
            # Delete first two items on list. Only columns to be updated remain
            del self.on_conflict[0:2]
            update_columns =
                ', '.join(["{0} = EXCLUDED.{0}".format(col) for col in self.on_conflict])
            return """
                ON CONFLICT ({0}) DO UPDATE SET {1};
                """.format(constraint, update_columns)
    else:
        return ";"

I tested it out and it seems to work well. I understand it's not the most pythonic solution though

an example would be:
Customers.objects.from_csv('/path/to/file.csv', on_conflict=['DO UPDATE', 'name', 'email'])
with multiple fields to update:
Customers.objects.from_csv('/path/to/file.csv', on_conflict=['DO UPDATE', 'name', 'email', 'active', 'age'])
or in plain english:
if field on column 'name' already exists, update 'email', 'active' and 'age' fields

Is ON CONFLICT DO UPDATE; possible? #91

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