text: #  Copyright 2021 Collate
  #  Licensed under the Apache License, Version 2.0 (the "License");
  #  you may not use this file except in compliance with the License.
  #  You may obtain a copy of the License at
  #  http://www.apache.org/licenses/LICENSE-2.0
  #  Unless required by applicable law or agreed to in writing, software
  #  distributed under the License is distributed on an "AS IS" BASIS,
  #  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  #  See the License for the specific language governing permissions and
  #  limitations under the License.
  
  """
  Null Count Metric definition
  """
  # pylint: disable=duplicate-code
  
  from sqlalchemy import case, column, func
  
  from metadata.orm_profiler.metrics.core import StaticMetric, _label
  
  
  class NullCount(StaticMetric):
      """
      NULL COUNT Metric
  
      Given a column, return the null count.
  
      We are building a CASE WHEN structure:
      ```
      SUM(
          CASE is not null THEN 1
          ELSE 0
      )
      ```
      """
  
      @classmethod
      def name(cls):
          return "nullCount"
  
      @property
      def metric_type(self):
          return int
  
      @_label
      def fn(self):
          return func.sum(case([(column(self.col.name).is_(None), 1)], else_=0))
  