Chris/remove redirect from slice id endpoint

[williaster]

@mistercrunch

I used the approach we discussed yesterday for avoiding a re-direct for the /caravel/slice/id endpoint. It required a bit of refactoring of the explore method but not too bad. Overall if a slice_id is passed as part of the URL pathname I'll use that, then fall back to the URL query, else None.

In the case that a slice_id is found I update the database slice params with any specified in the URL. I coerce the updated param dict to a ImmutableMultiDict so that its type is consistent with request.args. I ran into a reported MultiDict bug wherein if you initialize an ImmutableMultiDict with a dict containing a key whose value is an empty array, if you try to access that key, an IndexError is thrown. I added a try catch for this where I was seeing errors. eg:

md = MultiDict({ groupby: [] })
md.keys() # returns ['groupby']
md['groupby'] # IndexError
md.get('groupby') # IndexError

As noted I also found another bug where slices that have been over-written are saved with the original slice_id which caused weird bugs in the forms. I fixed this in the save_slice_as method and explicitly set the slice_id in the slice_params I use to the value passed in the URL.

Updated tests / they all passed.

[mistercrunch]

pythonesque coalesce:
silce_id = slice_id or request.args.get('slice_id')

[williaster]

does this work for slice_id = 0 because slice_id is actually a string? thinking too much in JS.

[bkyryliuk]

you can do int(request.args.get("slice_id"))

[mistercrunch]

Code looks good, but Travis says no :(

[williaster]

yeah js linting error. didn't change any js so will look into what's up.