6. Signals

Django ships with the following signals for database operations:

• Saving a single instance: pre_save and post_save
• Deleting data: pre_delete and post_delete
• Changing a many to many relationship: m2m_changed

Missing from this list is the ability to attach signals before and after updating data and bulk-creating data.

6.1. Bulk-create signals

The following signals are fired when data is created in bulk:

• pre_bulk_create is fired just before data is created
• post_bulk_create is fired just after data is created

For copying data into the database from a buffer (i.e., using copy_from_instances):

• pre_copy_from_instances is fired just before data is copied
• post_copy_from_instances is fired just after data is copied

6.2. Update signals

There are three sets of signals attached to the three ways you can update data.

For homogeneous updates (i.e., use the classic update()):

• pre_update is fired just before data is updated
• post_update is fired just after data is updated

For heterogeneous updates (i.e., using update_fields()):

• pre_update_fields is fired just before data is updated
• post_update_fields is fired just after data is updated

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See Siganls Reference for more details.