在 Django 中流式传输 CSV 文件

Posted 2023-02-23

【中文标题】在 Django 中流式传输 CSV 文件

【英文标题】：Streaming a CSV file in Django

【发布时间】：2011-07-06 00:22:37

【问题描述】：

我正在尝试将 csv 文件作为附件下载流式传输。 CSV 文件的大小将达到 4MB 或更大，我需要一种方法让用户主动下载文件，而无需等待所有数据被创建并首先提交到内存。

我首先使用了我自己的基于 Django 的 FileWrapper 类的文件包装器。那失败了。然后我在这里看到了一种使用生成器流式传输响应的方法： How to stream an HttpResponse with Django

当我在生成器中引发错误时，我可以看到我正在使用 get_row_data() 函数创建正确的数据，但是当我尝试返回响应时，它返回为空。我还禁用了 Django GZipMiddleware。有谁知道我做错了什么？

编辑：我遇到的问题是ConditionalGetMiddleware。我不得不替换它，代码在下面的答案中。

这里是视图：

from django.views.decorators.http import condition

@condition(etag_func=None)
def csv_view(request, app_label, model_name):
    """ Based on the filters in the query, return a csv file for the given model """

    #Get the model
    model = models.get_model(app_label, model_name)

    #if there are filters in the query
    if request.method == 'GET':
        #if the query is not empty
        if request.META['QUERY_STRING'] != None:
            keyword_arg_dict = 
            for key, value in request.GET.items():
                #get the query filters
                keyword_arg_dict[str(key)] = str(value)
            #generate a list of row objects, based on the filters
            objects_list = model.objects.filter(**keyword_arg_dict)
        else:
            #get all the model's objects
            objects_list = model.objects.all()
    else:
        #get all the model's objects
        objects_list = model.objects.all()
    #create the reponse object with a csv mimetype
    response = HttpResponse(
        stream_response_generator(model, objects_list),
        mimetype='text/plain',
        )
    response['Content-Disposition'] = "attachment; filename=foo.csv"
    return response

这是我用来流式传输响应的生成器：

def stream_response_generator(model, objects_list):
    """Streaming function to return data iteratively """
    for row_item in objects_list:
        yield get_row_data(model, row_item)
        time.sleep(1)

这是我创建 csv 行数据的方法：

def get_row_data(model, row):
    """Get a row of csv data from an object"""
    #Create a temporary csv handle
    csv_handle = cStringIO.StringIO()
    #create the csv output object
    csv_output = csv.writer(csv_handle)
    value_list = [] 
    for field in model._meta.fields:
        #if the field is a related field (ForeignKey, ManyToMany, OneToOne)
        if isinstance(field, RelatedField):
            #get the related model from the field object
            related_model = field.rel.to
            for key in row.__dict__.keys():
                #find the field in the row that matches the related field
                if key.startswith(field.name):
                    #Get the unicode version of the row in the related model, based on the id
                    try:
                        entry = related_model.objects.get(
                            id__exact=int(row.__dict__[key]),
                            )
                    except:
                        pass
                    else:
                        value = entry.__unicode__().encode("utf-8")
                        break
        #if it isn't a related field
        else:
            #get the value of the field
            if isinstance(row.__dict__[field.name], basestring):
                value = row.__dict__[field.name].encode("utf-8")
            else:
                value = row.__dict__[field.name]
        value_list.append(value)
    #add the row of csv values to the csv file
    csv_output.writerow(value_list)
    #Return the string value of the csv output
    return csv_handle.getvalue()

【参考方案1】：

这里有一些可以流式传输 CSV 的简单代码；你可能可以从这里开始你需要做的任何事情：

import cStringIO as StringIO
import csv

def csv(request):
    def data():
        for i in xrange(10):
            csvfile = StringIO.StringIO()
            csvwriter = csv.writer(csvfile)
            csvwriter.writerow([i,"a","b","c"])
            yield csvfile.getvalue()

    response = HttpResponse(data(), mimetype="text/csv")
    response["Content-Disposition"] = "attachment; filename=test.csv"
    return response

这只是将每一行写入内存文件，读取该行并生成它。

此版本生成批量数据效率更高，但使用前请务必了解以上内容：

import cStringIO as StringIO
import csv

def csv(request):
    csvfile = StringIO.StringIO()
    csvwriter = csv.writer(csvfile)

    def read_and_flush():
        csvfile.seek(0)
        data = csvfile.read()
        csvfile.seek(0)
        csvfile.truncate()
        return data

    def data():
        for i in xrange(10):
            csvwriter.writerow([i,"a","b","c"])
        data = read_and_flush()
        yield data

    response = HttpResponse(data(), mimetype="text/csv")
    response["Content-Disposition"] = "attachment; filename=test.csv"
    return response

【讨论】：

我还没有需要流式传输数据，但很高兴知道获得简单而优雅的东西有多快。

虽然我真的很喜欢这个答案，但事实证明这不是我的问题。我真的使用了你写的这个确切的代码，只是为了看看它是否会产生一个响应，但响应返回为 0 字节。所以我仍然坚持同样的结果。

此代码运行良好，因此您的环境有问题需要排除故障。

看来禁用 ConditionalGetMiddleware 实际上会允许发回响应。不过，我真的更愿意启用该中间件。有没有办法使用生成器并保持该中间件处于启用状态？

此解决方案的更新是使用 Django 1.5 中的新 StreamingHttpResponse。 :)

【参考方案2】：

从 Django 1.5 开始，中间件问题已得到解决，并引入了 StreamingHttpResponse。应该这样做：

import cStringIO as StringIO
import csv

def csv_view(request):
    ...
    # Assume `rows` is an iterator or lists
    def stream():
        buffer_ = StringIO.StringIO()
        writer = csv.writer(buffer_)
        for row in rows:
            writer.writerow(row)
            buffer_.seek(0)
            data = buffer_.read()
            buffer_.seek(0)
            buffer_.truncate()
            yield data
    response = StreamingHttpResponse(
        stream(), content_type='text/csv'
    )
    disposition = "attachment; filename=file.csv"
    response['Content-Disposition'] = disposition
    return response

how to output csv from Django 上有一些文档，但它没有利用 StreamingHttpResponse，所以我继续使用 opened a ticket in order to track it。

【参考方案3】：

我遇到的问题是 ConditionalGetMiddleware。我看到 django-piston 为 ConditionalGetMiddleware 提供了一个替代中间件，它允许流式传输：

from django.middleware.http import ConditionalGetMiddleware

def compat_middleware_factory(klass):
    """
    Class wrapper that only executes `process_response`
    if `streaming` is not set on the `HttpResponse` object.
    Django has a bad habbit of looking at the content,
    which will prematurely exhaust the data source if we're
    using generators or buffers.
    """
    class compatwrapper(klass):
        def process_response(self, req, resp):
            if not hasattr(resp, 'streaming'):
                return klass.process_response(self, req, resp)
            return resp
    return compatwrapper

ConditionalMiddlewareCompatProxy = compat_middleware_factory(ConditionalGetMiddleware)

那么您将用您的 ConditionalMiddlewareCompatProxy 中间件替换 ConditionalGetMiddleware，并且在您看来（从一个聪明的答案中借用代码）：

def csv_view(request):
    def data():
        for i in xrange(10):
            csvfile = StringIO.StringIO()
            csvwriter = csv.writer(csvfile)
            csvwriter.writerow([i,"a","b","c"])
            yield csvfile.getvalue()

    #create the reponse object with a csv mimetype
    response = HttpResponse(
        data(),
        mimetype='text/csv',
        )
    #Set the response as an attachment with a filename
    response['Content-Disposition'] = "attachment; filename=test.csv"
    response.streaming = True
    return response