Need a consistent way to request JSON output

1) You can set tg.allow_json to True in your project's app.cfg file to allow tg_format=json for all exposed methods.

2) I think, you need rethink your app's URL interface. Either an exposed method always returns JSON, then the client-side JS should know this and use a URL without tg_format=json, or the method can return JSON and something else (HTML), then the server needs something to distinguish between request for the two return data formats. You have the control over the client code, so why can't you specify which resource you want to request?

3) You can also use the Accept request header to specify the return data format:

http://docs.turbogears.org/1.0/ExposeDecorator#id3

I'm inclined to resolve this ticket as "wontfix". Convince us, if you disagree.

Replying to Chris Arndt:

1) You can set tg.allow_json to True in your project's app.cfg file to allow tg_format=json for all exposed methods.

This is a true statement but not what I'm asking for. There should still be URLs that are not accessible via JSON.

2) I think, you need rethink your app's URL interface. Either an exposed method always returns JSON, then the client-side JS should know this and use a URL without tg_format=json, or the method can return JSON and something else (HTML), then the server needs something to distinguish between request for the two return data formats. You have the control over the client code, so why can't you specify which resource you want to request?

I think your assumption is wrong. Why should the client code need to know that specifying tg_format=json is illegal? Why does it need to know that a particular URL always or sometimes returns JSON? The server cares because it needs to know whether it's supposed to deliver html or JSON but all the client cares is that it makes a request and gets data back in the format it desires. Why should the client care that it *must* specify:

http://localhost:8080/json_only_data/ http://localhost:8080/html_or_json/?tg_format=json

The client should be able to specify

http://localhost:8080/json_only_data/?tg_format=json http://localhost:8080/html_or_json/?tg_format=json

and if the server has an @expose that handles json, then it will do the right thing. Making it so the second case doesn't work adds an unnecessary extra piece of information for the client to deal with. If the server suddenly stops providing an html view of the data at the same URL, it will break the client even though, for the client, nothing has changed.

Also, this is even more inconsistent than I first thought: These cases take a tg_format query param::

@expose('templates.welcome', allow_json=True) def public_method(self):

@expose(allow_json=True) def public_method(self):

@expose('templates.welcome') @expose('json') def public_method(self):

This case does not:

@expose('json') def public_method(self):

So it looks like the single expose decorator is a special case. Why do you think it is necessary for the server to disallow tg_format=json in this case?

3) You can also use the Accept request header to specify the return data format: http://docs.turbogears.org/1.0/ExposeDecorator#id3

While using the accept header is fine for writing into my client library routine, it is harder to test that the server is behaving when you have to inject a header rather than specifying a simple query param on the commandline. It's also harder for an end user creating a third party script that supplements whatever I'm officially providing to discover and use.

I think this makes sense. Fixed in r4727.