python - 手动添加行到 StreamingHttpResponse (Django)

Question

我正在使用 Django 的 StreamingHttpResponse 动态传输大型 CSV 文件。根据the docs ，迭代器被传递给响应的 streaming_content 参数:

import csv
from django.http import StreamingHttpResponse

def get_headers():
    return ['field1', 'field2', 'field3']

def get_data(item):
    return {
        'field1': item.field1,
        'field2': item.field2,
        'field3': item.field3,
    }

# StreamingHttpResponse requires a File-like class that has a 'write' method
class Echo(object):
    def write(self, value):
        return value


def get_response(queryset):
    writer = csv.DictWriter(Echo(), fieldnames=get_headers())
    writer.writeheader() # this line does not work

    response = StreamingHttpResponse(
        # the iterator
        streaming_content=(writer.writerow(get_data(item)) for item in queryset),
        content_type='text/csv',
    )
    response['Content-Disposition'] = 'attachment;filename=items.csv'

    return response

我的问题是:如何在 CSV 编写器上手动写入一行？手动调用 writer.writerow(data) 或 writer.writeheader()(也在内部调用 writerow())似乎不会写入数据集，而只有来自 streaming_content 的生成/流式数据写入输出数据集。

Answer 1

答案是使用生成器函数生成结果，而不是动态计算它们(在 StreamingHttpResponse 的 streaming_content 参数中)并使用我们创建的伪缓冲区(Echo 类)来写入一行响应:

import csv
from django.http import StreamingHttpResponse

def get_headers():
    return ['field1', 'field2', 'field3']

def get_data(item):
    return {
        'field1': item.field1,
        'field2': item.field2,
        'field3': item.field3,
    }

# StreamingHttpResponse requires a File-like class that has a 'write' method
class Echo(object):
    def write(self, value):
        return value

def iter_items(items, pseudo_buffer):
    writer = csv.DictWriter(pseudo_buffer, fieldnames=get_headers())
    yield pseudo_buffer.write(get_headers())

    for item in items:
        yield writer.writerow(get_data(item))

def get_response(queryset):
    response = StreamingHttpResponse(
        streaming_content=(iter_items(queryset, Echo())),
        content_type='text/csv',
    )
    response['Content-Disposition'] = 'attachment;filename=items.csv'
    return response