Custom rest endpoint for Up

[zzgvh]

The old Tastypie based API is struggling when Up requests all projects for large organisations. This is probably due to the nature of the code that returns the data, possibly in combination with Postgres being slower than MySQL for this complicated query.

Since we want to move away from the Tastypie API anyway, this seems like a good time to create a custom endpoint in RSR's new, DRF-based API.

The new endpoint will include the full Project model, including any thumbnails of current_image and also the Primary location as an inline object.

[zzgvh]

Test plan

This PR adds new functionality to the rest API for the models that have an image, i.e. Project, Organisation and ProjectUpdate.

By default the image field for those models now return a path to a thumbnail. This thumb is 191px wide, the format used by the updates on akvo.org.

The larger change/addition this feature adds is that it's now possible to request thumbnails and specify their size. The size is specified by either width or height to get the image to scale correctly in the other dimension or to specify both thereby setting an absolute maximum size of the image, while keeping the aspect ratio.

Example:

An example is the easiest way to show what's going on. Calling http://rsr.test.akvo.org/rest/v1/project/?image_thumb_name=big,small&image_thumb_small_width=90&image_thumb_big_max_size=300x200 should result in the returned JSON including somthing like

...
"current_image": {
    "default": "/media/cache/86/12/8612ee8e96c3f34ea213f8e1f8a06666.jpg",
    "big": "/media/cache/39/14/3914d362ec01ac9f8d2f5483457a8ddb.jpg",
    "small": "/media/cache/5a/13/5a139c48492af14223ac24c8d7a9aa07.jpg",
    "original": "/media/db/project/16/Project_16_current_image_2015-04-07_14.34.24.jpg"
}, 
...

for each project. Adding format=xml to the query and the result looks like:

...
<current_image>
    <default>/media/cache/86/12/8612ee8e96c3f34ea213f8e1f8a06666.jpg</default>
    <big>/media/cache/39/14/3914d362ec01ac9f8d2f5483457a8ddb.jpg</big>
    <small>/media/cache/5a/13/5a139c48492af14223ac24c8d7a9aa07.jpg</small>
    <original>/media/db/project/16/Project_16_current_image_2015-04-07_14.34.24.jpg</original>
</current_image>
...

Full testing

There are a number of combinations to test. The pattern for the query is thus:

/rest/v1/<endpoint>/?format=<API format>&image_thumb_name=<thumb identifiers>[&image_thumb_<name>_<dimension>=<dimension value>]

where

• <endpoint> is one of organisation, project, project_extra, project_up, project_update or project_update_extra
• <API format> is json or xml Can be omitted for JSON which is the default
• <thumb identifiers> is a comma separated list of names for the thumbs. If there's only one thumb no comma is needed
• <name> should match one of the names specified in <thumb identifiers>. The whole [&image_thumb__=] part must be repeated once for each name.
• <dimension> is one of width, height or max_size
• <dimension value> is an integer if <dimension> is width or height. If <dimension> is max_size then it should specify width and height separated by an x, e.g. 300x200.

Really thorough testing would include generating URLs for all combinations and checking that the generated thumbs are there and have the correct size. I think this is probably overkill though, since the underlying code is essentially the same for all API endpoints. For easier testing it might be better to use the single object API call, /rest/v1/<endpoint>/<object ID>/, followed by the query string.

Also, because thumbnails aren't created if there is no size specified, the degenerated query ?image_thumb_name=foo will return only the default thumgnail and the original, so this can be used if only the original is needed.

Testing Up

Up uses this call:

/rest/v1/project_up/?format=xml&image_thumb_name=up&image_thumb_up_width=<appropriate size>

Cache testing

To test the caching of thumbs, tests should include fetching an image using the same query string parameters several times and checking that the image path, and thus the image, is the same. This should hold for different users requesting a thumb with the same parameters and also for the same image using different endpoints, like project_update and project_update_extra.

Also test that the thumbnail changes if the original image is updated, for example if Project.current_image is changed.