Re: Best practice for server-generated downloads?

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Hi

+1 on this except that I use xlrd and xlwt to read and write Excel files. To generate the excel file I just generate a list of lists (an array effectively) and pass that through a function which walks the list and generates the excel worksheet that I write to a StringIO so it can be returned to the client.

François

On Oct 2, 2013, at 6:34 AM, Jirka Vejrazka <jirka.vejrazka@gmail.com> wrote:

> Hi Thomas,
>
> I'm doing exactly this - allowing users to download (graphically simple) XLSx files from my web app, it also needs to be available for download weeks later.
>
> As Russell pointed out, you don't need to store data on this if you have a way of getting the same set of data later, you can always regenerate the same Excel file. You don't even need to use StringIO for that.
>
> I'm using the save_virtual_notebook() in openpyxl package to generate the Excel file straight from database upon each (infrequent) request.
>
> HTH
>
> Jirka
>
>
> On Wed, Oct 2, 2013 at 9:36 AM, Russell Keith-Magee <russell@keith-magee.com> wrote:
>
> On Wed, Oct 2, 2013 at 2:33 PM, DJ-Tom <eventellis@gmail.com> wrote:
> Hi,
>
> this is quite easy to answer - those reports need to be archived - users must be able to download them days or weeks later.
>
> So I will create a record in a database for each report that is created so users can access it later - maybe this can be seen as "uploading" a file to the server that acts as a document repository, with the only difference that the file is not uploaded, but produced by the server.
>
> Well, if you need archival, there are two alternatives:
>
> 1. Write the file to disk at the same time it is being generated. There's no reason you have to serve the file from where it was generated -- generate it, write it, and serve it.
>
> 2. Make sure the report will always be generated the same way. An analog here -- if you request a page from a web server, it probably isn't saved on disk like that (unless it's a genuinely static page) -- the server knows how to reproduce the same page every time you request a specific URL. Make the reports the same -- if you request /report/September-2013, you generate the same report every time.
>
> The second approach depends on whether you have well time-bucketed data, but it's certainly possible to do.
>
> I don't see how I could use the xlsxwriter object in the way it is described here https://docs.djangoproject.com/en/1.5/howto/outputting-pdf/ - how could I pass the httpresponse object to xlsxWriter?
> (Maybe I have not yet found how this might work - but it is not what I need anyways...)
>
> I haven't used xlsxwriter myself, but the key part of the PDF example is that StringIO is an object that adheres to the python File API, but doesn't actually involve a file. So, you open a StringIO object, "write" to it, then dump the contents as the HTTP response.
>
> So - whatever API endpoint on xlsxwriter lets you pass in a file object -- pass in a StringIO instance instead.
>
> Yours,
> Russ Magee %-)
>
>
>
> Thomas
>
> Am Mittwoch, 2. Oktober 2013 02:11:21 UTC+2 schrieb Russell Keith-Magee:
>
> On Tue, Oct 1, 2013 at 9:49 PM, DJ-Tom <event...@gmail.com> wrote:
> Hi,
>
> I need to create database report downloads in Excel format (via xlsxwriter) and I'm wondering if there is any standard or best practice as to where those downloads should be located.
>
> Especially helpful would be if there was a portable way of managing the file system location and web request url in a way so that I don't have to change settings between the development and production server.
>
> Is this -> https://docs.djangoproject.com/en/1.5/topics/files/ the way to go?
>
> If they're sever generated, why do they need to hit the file system at all?
>
> The following example in the docs:
>
> https://docs.djangoproject.com/en/1.5/howto/outputting-pdf/
>
> shows how you can stream a report directly to the end user. The example uses reportlab to produce a PDF, but the same approach will work for a tool writing to a different format.
>
> Yours,
> Russ Magee %-)
>
>
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