Python/Bottle/MongoDB: Unsupported response type: <type 'dict'>

Question

@route('/locations', method='GET')
def get_location():
    entity = db['locations'].find({'coordinate2d': {'$near': [37.871593, -122.272747]}}).limit(3)
    if not entity:
        abort(404, 'No nearby locations')
    return entity

The response for the above portion of code is:

Error 500: Internal Server Error

Sorry, the requested URL 'http://localhost:8080/locations' caused an error:

Unsupported response type: <type 'dict'>

How can I grab that information from mongo as a type Bottle can return as JSON?

Answer 1

The complete solution was a combination of transforming the db cursor to a list, manually setting the response type + custom encoding the return value

@route('/locations/:lat/:lng', method='GET')
def get_location(lat,lng):
    response.content_type = 'application/json'
    objdb = db.locations.find({'coordinate2d': {'$near': [lat,lng]}}, {'coordinate2d':bool(1)}).skip(0).limit(3)
    entries = [entry for entry in objdb]
    return MongoEncoder().encode(entries)

In my case, produces this:

[
    {
        "_id": "4f4201bb7e720d1dca000005",
        "coordinate2d": [
            33.02032100000006,
            -117.19483074631853
        ]
    },
    {
        "_id": "4f4201587e720d1dca000002",
        "coordinate2d": [
            33.158092999999994,
            -117.350594
        ]
    },
    {
        "_id": "4f42018b7e720d1dca000003",
        "coordinate2d": [
            33.195870000000006,
            -117.379483
        ]
    }
]

Answer 2

As per the doc mention on bottle http://bottlepy.org/docs/dev/ you have to return the string from the @route decorator. You have to return the template with data or string.

If you want to generate the json then you have to change the Content-Type.

Dictionaries

As mentioned above, Python dictionaries (or subclasses thereof) are automatically transformed into JSON strings and returned to the browser with the Content-Type header set to application/json. This makes it easy to implement json-based APIs. Data formats other than json are supported too. See the tutorial-output-filter to learn more.

http://bottlepy.org/docs/dev/tutorial.html?highlight=json#generating-content

Answer 3

I got this error when I was trying to return a python list. I assumed it would translate into JSON, but it didn't. It made it to the line in bottle.py where it would handle iterables and found the first dict in the list and threw the error above.

To get around this, I simply embedded my list inside a dict.

return {'response': []}