old_contents: from __future__ import unicode_literals
  
  from django.db import models
  from django.utils.translation import ugettext_lazy as _
  
  from .managers import TemporalQuerySet
  
  
  class Department(models.Model):
      dept_no = models.CharField(primary_key=True, max_length=4)
      dept_name = models.CharField(unique=True, max_length=40)
  
      class Meta:
          db_table = 'departments'
          ordering = ['dept_no']
  
      def __str__(self):
          return self.dept_name
  
  
  class DeptEmp(models.Model):
      employee = models.ForeignKey('Employee', models.DO_NOTHING, db_column='emp_no')
      department = models.ForeignKey(Department, models.DO_NOTHING, db_column='dept_no')
      from_date = models.DateField()
      to_date = models.DateField()
  
      objects = TemporalQuerySet.as_manager()
  
      class Meta:
          db_table = 'dept_emp'
  
  
  class DeptManager(models.Model):
      employee = models.ForeignKey('Employee', models.DO_NOTHING, db_column='emp_no')
      department = models.ForeignKey(Department, models.DO_NOTHING, db_column='dept_no')
      from_date = models.DateField()
      to_date = models.DateField()
  
      objects = TemporalQuerySet.as_manager()
  
      class Meta:
          db_table = 'dept_manager'
          ordering = ['-from_date']
  
  
  class Employee(models.Model):
      emp_no = models.IntegerField(primary_key=True)
      birth_date = models.DateField()
      first_name = models.CharField(max_length=14)
      last_name = models.CharField(max_length=16)
      gender = models.CharField(max_length=1)
      hire_date = models.DateField()
  
      class Meta:
          db_table = 'employees'
  
      def __str__(self):
          return "{} {}".format(self.first_name, self.last_name)
  
  
  class Salary(models.Model):
      employee = models.ForeignKey(Employee, models.DO_NOTHING, db_column='emp_no')
      salary = models.IntegerField()
      from_date = models.DateField()
      to_date = models.DateField()
  
      objects = TemporalQuerySet.as_manager()
  
      class Meta:
          db_table = 'salaries'
          ordering = ['-from_date']
          verbose_name = _('Salary')
          verbose_name_plural = _('Salaries')
  
  
  class Title(models.Model):
      employee = models.ForeignKey(Employee, models.DO_NOTHING, db_column='emp_no')
      title = models.CharField(max_length=50)
      from_date = models.DateField()
      to_date = models.DateField(blank=True, null=True)
  
      objects = TemporalQuerySet.as_manager()
  
      class Meta:
          db_table = 'titles'
  
new_contents: from __future__ import unicode_literals
  
  from django.db import models
  from django.utils.translation import ugettext_lazy as _
  
  from .managers import TemporalQuerySet
  
  
  class Department(models.Model):
      dept_no = models.CharField(primary_key=True, max_length=4)
      dept_name = models.CharField(unique=True, max_length=40)
  
      class Meta:
          db_table = 'departments'
          ordering = ['dept_no']
  
      def __str__(self):
          return self.dept_name
  
  
  class DeptEmp(models.Model):
      employee = models.ForeignKey('Employee', on_delete=models.DO_NOTHING, db_column='emp_no')
      department = models.ForeignKey(Department, on_delete=models.DO_NOTHING, db_column='dept_no')
      from_date = models.DateField()
      to_date = models.DateField()
  
      objects = TemporalQuerySet.as_manager()
  
      class Meta:
          db_table = 'dept_emp'
  
  
  class DeptManager(models.Model):
      employee = models.ForeignKey('Employee', on_delete=models.DO_NOTHING, db_column='emp_no')
      department = models.ForeignKey(Department, on_delete=models.DO_NOTHING, db_column='dept_no')
      from_date = models.DateField()
      to_date = models.DateField()
  
      objects = TemporalQuerySet.as_manager()
  
      class Meta:
          db_table = 'dept_manager'
          ordering = ['-from_date']
  
  
  class Employee(models.Model):
      emp_no = models.IntegerField(primary_key=True)
      birth_date = models.DateField()
      first_name = models.CharField(max_length=14)
      last_name = models.CharField(max_length=16)
      gender = models.CharField(max_length=1)
      hire_date = models.DateField()
  
      class Meta:
          db_table = 'employees'
  
      def __str__(self):
          return "{} {}".format(self.first_name, self.last_name)
  
  
  class Salary(models.Model):
      employee = models.ForeignKey(Employee, on_delete=models.DO_NOTHING, db_column='emp_no')
      salary = models.IntegerField()
      from_date = models.DateField()
      to_date = models.DateField()
  
      objects = TemporalQuerySet.as_manager()
  
      class Meta:
          db_table = 'salaries'
          ordering = ['-from_date']
          verbose_name = _('Salary')
          verbose_name_plural = _('Salaries')
  
  
  class Title(models.Model):
      employee = models.ForeignKey(Employee, on_delete=models.DO_NOTHING, db_column='emp_no')
      title = models.CharField(max_length=50)
      from_date = models.DateField()
      to_date = models.DateField(blank=True, null=True)
  
      objects = TemporalQuerySet.as_manager()
  
      class Meta:
          db_table = 'titles'
  
subject: Fix employees demo for old django's