Generic CSV export admin action factory with relationship spanning fields and labels, and many to many fields

from django.http import HttpResponse
from django.db.models.query import QuerySet
from django.db.models.fields.files import FieldFile

import csv

def prep_field(request, obj, field, manyToManySep=';'):
    """ Returns the field as a unicode string. If the field is a callable, it
    attempts to call it first, without arguments.
    """
    if '__' in field:
        bits = field.split('__')
        field = bits.pop()
 
        for bit in bits:
            obj = getattr(obj, bit, None)
 
            if obj is None:
                return ""
 
    attr = getattr(obj, field)
    
    if isinstance(attr, (FieldFile,) ):
        attr = request.build_absolute_uri(attr.url)
        
    output = attr() if callable(attr) else attr
    
    if isinstance(output, (list, tuple, QuerySet)):
        output = manyToManySep.join([str(item) for item in output])
    return unicode(output).encode('utf-8') if output else ""
 
 
def export_csv_action(description="Export as CSV", fields=None, exclude=None, header=True,
                      manyToManySep=';'):
    """ This function returns an export csv action. """
    def export_as_csv(modeladmin, request, queryset):
        """ Generic csv export admin action.
        Based on http://djangosnippets.org/snippets/2712/
        """
        opts = modeladmin.model._meta
        field_names = [field.name for field in opts.fields]
        labels = []
 
        if exclude:
            field_names = [f for f in field_names if f not in exclude]
 
        elif fields:
            field_names = [field for field, _ in fields]
            labels = [label for _, label in fields]
 
        response = HttpResponse(mimetype='text/csv')
        response['Content-Disposition'] = 'attachment; filename=%s.csv' % (
                unicode(opts).replace('.', '_')
            )
 
        writer = csv.writer(response)
 
        if header:
            writer.writerow(labels if labels else field_names)
 
        for obj in queryset:
            writer.writerow([prep_field(request, obj, field, manyToManySep) for field in field_names])
        return response
    export_as_csv.short_description = description
    export_as_csv.acts_on_all = True
    return export_as_csv

# Example usage

from django.contrib import admin

 
class ExampleModelAdmin(admin.ModelAdmin):
    raw_id_fields = ('field1',)
    list_display = ('field1', 'field2', 'field3',)
    actions = [
        export_csv_action("Export Sepecial Report",
            fields=[
                ('field1', 'label1'),
                ('foreignkey1__name', 'label2'),
                ('manytomany__all', 'label3'),
            ],
            header=True,
            manyToManySep=';'
        ),
    ]
 
admin.site.register(ExampleMode, ExampleModelAdmin)