title: Filter rows from Excel on import with Django Import-Export
body: <p>I have a new Django web-application (My first one in python) and im using Import-export in the admin section to take an excel file and upload it to my database.the upload works perfectly, but I need to add two features:</p>
  <ol>
  <li>Is there a way to truncate all the existing data in the application database table before the upload?</li>
  <li>What is the best way to filter out rows from the Excel file that don't match a condition (if column value of a row != X)</li>
  </ol>
  <p>I have read the documentation and it seems like for question 2, the only option is to implement an for_delete method. I find it hard to believe this is the best way, but im brand new to python and Django.</p>
  <p>here is my resource class</p>
  <pre><code>from django.contrib import admin
  from .models import Sale
  from import_export.admin import ImportExportModelAdmin
  from import_export import resources, fields
  from import_export.fields import Field
      
  class SaleResource(resources.ModelResource):
      
      myColumn = fields.Field(attribute='myColumn', column_name=&quot;my_Column&quot;)
      
  
      class Meta:
          model = Sale
  
          def skip_row(self, instance, original):
              val = self.myColumn
              if val != 'myValue':
                  return True
  
  
  
  @admin.register(Sale)
  class SaleAdmin(ImportExportModelAdmin):
      resource_class = SaleResource
  </code></pre>