For a many2many field, a list of tuples is expected. Here is the list of tuples that are accepted, with the corresponding semantics:

• (0, 0, { values }) link to a new record that needs to be created with the given values dictionary
• (1, ID, { values }) update the linked record with id = ID (write values on it)
• (2, ID) remove and delete the linked record with id = ID (calls unlink on ID, which will delete the object completely, and the link to it as well)
• (3, ID) cut the link to the linked record with id = ID (delete the relationship between the two objects but do not delete the target object itself)
• (4, ID) link to existing record with id = ID (adds a relationship)
• (5) unlink all (like using (3,ID) for all linked records)
• (6, 0, [IDs]) replace the list of linked IDs (like using (5) then (4,ID) for each ID in the list of IDs)