169 lines
6.3 KiB
Python
169 lines
6.3 KiB
Python
"""
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Utilities for django models.
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"""
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from django.conf import settings
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from django.dispatch import Signal
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from django_countries.fields import Country
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from eventtracking import tracker
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# The setting name used for events when "settings" (account settings, preferences, profile information) change.
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USER_SETTINGS_CHANGED_EVENT_NAME = u'edx.user.settings.changed'
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# Used to signal a field value change
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USER_FIELD_CHANGED = Signal(providing_args=["user", "table", "setting", "old_value", "new_value"])
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def get_changed_fields_dict(instance, model_class):
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"""
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Helper method for tracking field changes on a model.
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Given a model instance and class, return a dict whose keys are that
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instance's fields which differ from the last saved ones and whose values
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are the old values of those fields. Related fields are not considered.
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Args:
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instance (Model instance): the model instance with changes that are
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being tracked
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model_class (Model class): the class of the model instance we are
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tracking
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Returns:
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dict: a mapping of field names to current database values of those
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fields, or an empty dict if the model is new
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"""
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try:
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old_model = model_class.objects.get(pk=instance.pk)
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except model_class.DoesNotExist:
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# Object is new, so fields haven't technically changed. We'll return
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# an empty dict as a default value.
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return {}
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else:
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# We want to compare all of the scalar fields on the model, but none of
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# the relations.
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field_names = [f.name for f in model_class._meta.get_fields() if not f.is_relation] # pylint: disable=protected-access
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changed_fields = {
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field_name: getattr(old_model, field_name) for field_name in field_names
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if getattr(old_model, field_name) != getattr(instance, field_name)
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}
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return changed_fields
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def emit_field_changed_events(instance, user, db_table, excluded_fields=None, hidden_fields=None):
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"""Emits a settings changed event for each field that has changed.
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Note that this function expects that a `_changed_fields` dict has been set
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as an attribute on `instance` (see `get_changed_fields_dict`.
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Args:
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instance (Model instance): the model instance that is being saved
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user (User): the user that this instance is associated with
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db_table (str): the name of the table that we're modifying
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excluded_fields (list): a list of field names for which events should
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not be emitted
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hidden_fields (list): a list of field names specifying fields whose
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values should not be included in the event (None will be used
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instead)
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Returns:
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None
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"""
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def clean_field(field_name, value):
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"""
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Prepare a field to be emitted in a JSON serializable format. If
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`field_name` is a hidden field, return None.
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"""
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if field_name in hidden_fields:
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return None
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# Country is not JSON serializable. Return the country code.
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if isinstance(value, Country):
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if value.code:
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return value.code
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else:
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return None
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return value
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excluded_fields = excluded_fields or []
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hidden_fields = hidden_fields or []
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changed_fields = getattr(instance, '_changed_fields', {})
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for field_name in changed_fields:
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if field_name not in excluded_fields:
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old_value = clean_field(field_name, changed_fields[field_name])
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new_value = clean_field(field_name, getattr(instance, field_name))
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emit_setting_changed_event(user, db_table, field_name, old_value, new_value)
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# Remove the now inaccurate _changed_fields attribute.
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if hasattr(instance, '_changed_fields'):
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del instance._changed_fields
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def truncate_fields(old_value, new_value):
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"""
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Truncates old_value and new_value for analytics event emission if necessary.
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Args:
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old_value(obj): the value before the change
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new_value(obj): the new value being saved
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Returns:
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a dictionary with the following fields:
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'old': the truncated old value
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'new': the truncated new value
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'truncated': the list of fields that have been truncated
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"""
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# Compute the maximum value length so that two copies can fit into the maximum event size
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# in addition to all the other fields recorded.
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max_value_length = settings.TRACK_MAX_EVENT / 4
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serialized_old_value, old_was_truncated = _get_truncated_setting_value(old_value, max_length=max_value_length)
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serialized_new_value, new_was_truncated = _get_truncated_setting_value(new_value, max_length=max_value_length)
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truncated_values = []
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if old_was_truncated:
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truncated_values.append("old")
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if new_was_truncated:
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truncated_values.append("new")
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return {'old': serialized_old_value, 'new': serialized_new_value, 'truncated': truncated_values}
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def emit_setting_changed_event(user, db_table, setting_name, old_value, new_value):
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"""Emits an event for a change in a setting.
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Args:
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user (User): the user that this setting is associated with.
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db_table (str): the name of the table that we're modifying.
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setting_name (str): the name of the setting being changed.
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old_value (object): the value before the change.
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new_value (object): the new value being saved.
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Returns:
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None
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"""
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truncated_fields = truncate_fields(old_value, new_value)
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truncated_fields['setting'] = setting_name
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truncated_fields['user_id'] = user.id
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truncated_fields['table'] = db_table
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tracker.emit(
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USER_SETTINGS_CHANGED_EVENT_NAME,
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truncated_fields
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)
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# Announce field change
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USER_FIELD_CHANGED.send(sender=None, user=user, table=db_table, setting=setting_name,
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old_value=old_value, new_value=new_value)
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def _get_truncated_setting_value(value, max_length=None):
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"""
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Returns the truncated form of a setting value.
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Returns:
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truncated_value (object): the possibly truncated version of the value.
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was_truncated (bool): returns true if the serialized value was truncated.
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"""
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if isinstance(value, basestring) and max_length is not None and len(value) > max_length:
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return value[0:max_length], True
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else:
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return value, False
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