from peewee import * from playhouse.sqlite_ext import JSONField class BaseChangeLog(Model): timestamp = DateTimeField(constraints=[SQL('DEFAULT CURRENT_TIMESTAMP')]) action = TextField() table = TextField() primary_key = IntegerField() changes = JSONField() class ChangeLog(object): # Model class that will serve as the base for the changelog. This model # will be subclassed and mapped to your application database. base_model = BaseChangeLog # Template for the triggers that handle updating the changelog table. # table: table name # action: insert / update / delete # new_old: NEW or OLD (OLD is for DELETE) # primary_key: table primary key column name # column_array: output of build_column_array() # change_table: changelog table name template = """CREATE TRIGGER IF NOT EXISTS %(table)s_changes_%(action)s AFTER %(action)s ON %(table)s BEGIN INSERT INTO %(change_table)s ("action", "table", "primary_key", "changes") SELECT '%(action)s', '%(table)s', %(new_old)s."%(primary_key)s", "changes" FROM ( SELECT json_group_object( col, json_array( case when json_valid("oldval") then json("oldval") else "oldval" end, case when json_valid("newval") then json("newval") else "newval" end) ) AS "changes" FROM ( SELECT json_extract(value, '$[0]') as "col", json_extract(value, '$[1]') as "oldval", json_extract(value, '$[2]') as "newval" FROM json_each(json_array(%(column_array)s)) WHERE "oldval" IS NOT "newval" ) ); END;""" drop_template = 'DROP TRIGGER IF EXISTS %(table)s_changes_%(action)s' _actions = ('INSERT', 'UPDATE', 'DELETE') def __init__(self, db, table_name='changelog'): self.db = db self.table_name = table_name def _build_column_array(self, model, use_old, use_new, skip_fields=None): # Builds a list of SQL expressions for each field we are tracking. This # is used as the data source for change tracking in our trigger. col_array = [] for field in model._meta.sorted_fields: if field.primary_key: continue if skip_fields is not None and field.name in skip_fields: continue column = field.column_name new = 'NULL' if not use_new else 'NEW."%s"' % column old = 'NULL' if not use_old else 'OLD."%s"' % column if isinstance(field, JSONField): # Ensure that values are cast to JSON so that the serialization # is preserved when calculating the old / new. if use_old: old = 'json(%s)' % old if use_new: new = 'json(%s)' % new col_array.append("json_array('%s', %s, %s)" % (column, old, new)) return ', '.join(col_array) def trigger_sql(self, model, action, skip_fields=None): assert action in self._actions use_old = action != 'INSERT' use_new = action != 'DELETE' cols = self._build_column_array(model, use_old, use_new, skip_fields) return self.template % { 'table': model._meta.table_name, 'action': action, 'new_old': 'NEW' if action != 'DELETE' else 'OLD', 'primary_key': model._meta.primary_key.column_name, 'column_array': cols, 'change_table': self.table_name} def drop_trigger_sql(self, model, action): assert action in self._actions return self.drop_template % { 'table': model._meta.table_name, 'action': action} @property def model(self): if not hasattr(self, '_changelog_model'): class ChangeLog(self.base_model): class Meta: database = self.db table_name = self.table_name self._changelog_model = ChangeLog return self._changelog_model def install(self, model, skip_fields=None, drop=True, insert=True, update=True, delete=True, create_table=True): ChangeLog = self.model if create_table: ChangeLog.create_table() actions = list(zip((insert, update, delete), self._actions)) if drop: for _, action in actions: self.db.execute_sql(self.drop_trigger_sql(model, action)) for enabled, action in actions: if enabled: sql = self.trigger_sql(model, action, skip_fields) self.db.execute_sql(sql)