Django CSV出力のちょっと面倒くさい話(1)

admin-1.py

"""HttpResponseを使う場合"""
import csv

from django.contrib import admin
from django.http.response import HttpResponse

from .models import Book


def export_as_csv(modeladmin, request, queryset):
    meta = modeladmin.model._meta
    field_names = [field.name for field in meta.fields]

    response = HttpResponse(content_type='text/csv')
    response['Content-Disposition'] = f'attachment; filename={meta.label_lower}.csv'
    writer = csv.writer(response)

    writer.writerow(field_names)
    for obj in queryset:
        writer.writerow([getattr(obj, field) for field in field_names])
    return response


export_as_csv.short_description = "CSVエクスポート"


class BookAdmin(admin.ModelAdmin):
    actions = (export_as_csv,)


admin.site.register(Book, BookAdmin)

admin-2.py

"""StreamingHttpResponseを使う場合（大容量のファイルをダウンロードするならこちらが良い）"""
import csv

from django.contrib import admin
from django.http import StreamingHttpResponse

from .models import Book


class Echo:
    def write(self, value):
        return value


def _get_csv_rows(fields, queryset):
    field_names = [field.name for field in fields]
    yield field_names

    for obj in queryset:
        yield [getattr(obj, field) for field in field_names]


def export_as_csv(modeladmin, request, queryset):
    meta = modeladmin.model._meta

    pseudo_buffer = Echo()
    writer = csv.writer(pseudo_buffer)

    rows = _get_csv_rows(fields=meta.fields, queryset=queryset)
    response = StreamingHttpResponse(
        (writer.writerow(row) for row in rows),
        content_type='text/csv',
    )
    response['Content-Disposition'] = f'attachment; filename={meta.label_lower}.csv'
    return response


export_as_csv.short_description = "CSVエクスポート"


class BookAdmin(admin.ModelAdmin):
    actions = (export_as_csv,)


admin.site.register(Book, BookAdmin)