"""
Utilities for django models.
"""
import unicodedata
import re
from eventtracking import tracker
from django.conf import settings
from django.utils.encoding import force_unicode
from django.utils.safestring import mark_safe
from django_countries.fields import Country
# The setting name used for events when "settings" (account settings, preferences, profile information) change.
USER_SETTINGS_CHANGED_EVENT_NAME = u'edx.user.settings.changed'
def get_changed_fields_dict(instance, model_class):
"""
Helper method for tracking field changes on a model.
Given a model instance and class, return a dict whose keys are that
instance's fields which differ from the last saved ones and whose values
are the old values of those fields. Related fields are not considered.
Args:
instance (Model instance): the model instance with changes that are
being tracked
model_class (Model class): the class of the model instance we are
tracking
Returns:
dict: a mapping of field names to current database values of those
fields, or an empty dict if the model is new
"""
try:
old_model = model_class.objects.get(pk=instance.pk)
except model_class.DoesNotExist:
# Object is new, so fields haven't technically changed. We'll return
# an empty dict as a default value.
return {}
else:
field_names = [
field[0].name for field in model_class._meta.get_fields_with_model()
]
changed_fields = {
field_name: getattr(old_model, field_name) for field_name in field_names
if getattr(old_model, field_name) != getattr(instance, field_name)
}
return changed_fields
def emit_field_changed_events(instance, user, db_table, excluded_fields=None, hidden_fields=None):
"""Emits a settings changed event for each field that has changed.
Note that this function expects that a `_changed_fields` dict has been set
as an attribute on `instance` (see `get_changed_fields_dict`.
Args:
instance (Model instance): the model instance that is being saved
user (User): the user that this instance is associated with
db_table (str): the name of the table that we're modifying
excluded_fields (list): a list of field names for which events should
not be emitted
hidden_fields (list): a list of field names specifying fields whose
values should not be included in the event (None will be used
instead)
Returns:
None
"""
def clean_field(field_name, value):
"""
Prepare a field to be emitted in a JSON serializable format. If
`field_name` is a hidden field, return None.
"""
if field_name in hidden_fields:
return None
# Country is not JSON serializable. Return the country code.
if isinstance(value, Country):
if value.code:
return value.code
else:
return None
return value
excluded_fields = excluded_fields or []
hidden_fields = hidden_fields or []
changed_fields = getattr(instance, '_changed_fields', {})
for field_name in changed_fields:
if field_name not in excluded_fields:
old_value = clean_field(field_name, changed_fields[field_name])
new_value = clean_field(field_name, getattr(instance, field_name))
emit_setting_changed_event(user, db_table, field_name, old_value, new_value)
# Remove the now inaccurate _changed_fields attribute.
if hasattr(instance, '_changed_fields'):
del instance._changed_fields
def emit_setting_changed_event(user, db_table, setting_name, old_value, new_value):
"""Emits an event for a change in a setting.
Args:
user (User): the user that this setting is associated with.
db_table (str): the name of the table that we're modifying.
setting_name (str): the name of the setting being changed.
old_value (object): the value before the change.
new_value (object): the new value being saved.
Returns:
None
"""
# Compute the maximum value length so that two copies can fit into the maximum event size
# in addition to all the other fields recorded.
max_value_length = settings.TRACK_MAX_EVENT / 4
serialized_old_value, old_was_truncated = _get_truncated_setting_value(old_value, max_length=max_value_length)
serialized_new_value, new_was_truncated = _get_truncated_setting_value(new_value, max_length=max_value_length)
truncated_values = []
if old_was_truncated:
truncated_values.append("old")
if new_was_truncated:
truncated_values.append("new")
tracker.emit(
USER_SETTINGS_CHANGED_EVENT_NAME,
{
"setting": setting_name,
"old": serialized_old_value,
"new": serialized_new_value,
"truncated": truncated_values,
"user_id": user.id,
"table": db_table,
}
)
def _get_truncated_setting_value(value, max_length=None):
"""
Returns the truncated form of a setting value.
Returns:
truncated_value (object): the possibly truncated version of the value.
was_truncated (bool): returns true if the serialized value was truncated.
"""
if isinstance(value, basestring) and max_length is not None and len(value) > max_length:
return value[0:max_length], True
else:
return value, False
# Taken from Django 1.8 source code because it's not supported in 1.4
def slugify(value):
"""Converts value into a string suitable for readable URLs.
Converts to ASCII. Converts spaces to hyphens. Removes characters that
aren't alphanumerics, underscores, or hyphens. Converts to lowercase.
Also strips leading and trailing whitespace.
Args:
value (string): String to slugify.
"""
value = force_unicode(value)
value = unicodedata.normalize('NFKD', value).encode('ascii', 'ignore').decode('ascii')
value = re.sub(r'[^\w\s-]', '', value).strip().lower()
return mark_safe(re.sub(r'[-\s]+', '-', value))
def generate_unique_readable_id(name, queryset, lookup_field):
"""Generates a unique readable id from name by appending a numeric suffix.
Args:
name (string): Name to generate the id from. May include spaces.
queryset (QuerySet): QuerySet to check for uniqueness within.
lookup_field (string): Field name on the model that corresponds to the
unique identifier.
Returns:
string: generated unique identifier
"""
candidate = slugify(name)
conflicts = queryset.filter(**{lookup_field + '__startswith': candidate}).values_list(lookup_field, flat=True)
if conflicts and candidate in conflicts:
suffix = 2
while True:
new_id = candidate + '-' + str(suffix)
if new_id not in conflicts:
candidate = new_id
break
suffix += 1
return candidate