Eve-Demo

A fully featured RESTful Web API powered by Eve. With Eve setting up an API is very simple. You just need a launch script (run.py) and a configuration module (settings.py).

Note. The demo is currently running v0.0.3 of the Eve framework. Eve-Demo is only updated when major Eve updates are released. Please refer to the official Eve repository for an up-to-date features list.

Try it live

An instance of this code is running live at http://eve-demo.herokuapp.com. You can consume the API by using cURL or, if you are on Chrome, you might want to give a shot at the Advanced REST Client extension.

There is also a sample client application available. It uses the Requests library to consume the demo. In fact it has been quickly hacked together to reset the API every once in a while. Check it out at https://github.com/nicolaiarocci/eve-demo-client.

API Entry Point

A GET request sent to the API entry point (the home page) will obtain a list of available resources:

$ curl -i http://eve-demo.herokuapp.com

Response:

TTP/1.0 200 OK
Content-Type: application/json
Content-Length: 101
Cache-Control: max-age=20
Expires: Sat, 15 Feb 2014 15:52:57 GMT
Server: Eve/0.3 Werkzeug/0.9.4 Python/2.7.3
Date: Sat, 15 Feb 2014 15:52:37 GMT

{
    "_links": {
        "child": [
            {"href": "eve-demo.herokuapp.com/works", "title": "works"},
            {"href": "eve-demo.herokuapp.com/people", "title": "people"}
        ]
    }
}

Every API endpoint exposes a _links dictionary containing one or more links to related resources. Dictionary keys express the relation (rel) between the resource and the endpoint. Values can be lists of links (such as in this case) or a single link. Links are dictionaries themselves where title is the human readable resource name and href the actual link to the resource. Links allow the client to eventually update its UI and/or transverse the API without any prior knoweledge of its structure: HATEOAS is at work here.

Cache Control

Notice how the response header contains cache-control directives (Cache-Control, Expires). Any Eve-powered API can easily control the values of these, both at global and individual endpoint level.

JSON and XML rendering

Since we did not provide an Accept header with our request, the API responded with the default Content-Type: JSON.

$ curl -H "Accept: application/xml" -i http://eve-demo.herokuapp.com

Response:

HTTP/1.0 200 OK
Content-Type: application/xml; charset=utf-8
...

<resource>
    <link rel="child" href="eve-demo.herokuapp.com/works" title="works" />
    <link rel="child" href="eve-demo.herokuapp.com/people" title="people" />
</resource>

We requested XML this time. API responses will be rendered in JSON or XML depending on the requested mime-type.

Resource Endpoints

Clients can of course send requests to resource endpoints. With the previous request we learned that a people resource is available. Let's get it:

$ curl -i http://eve-demo.herokuapp.com/people

Response:

Content-Type: application/json
Content-Length: 2392
Cache-Control: max-age=20
Expires: Tue, 22 Jan 2013 10:04:43 GMT
Last-Modified: Wed, 05 Dec 2012 09:53:07 UTC
Server: Eve/0.0.3 Werkzeug/0.8.3 Python/2.7.3
Date: Tue, 22 Jan 2013 10:04:23 GMT


{
    "_items": [
        {
            "firstname": "Mark",
            "lastname": "Green",
            "born": "Sat, 23 Feb 1985 12:00:00 UTC",
            "role": ["copy", "author"],
            "location": {"city": "New York", "address": "4925 Lacross Road"},
            "_id": "50bf198338345b1c604faf31",
            "_updated": "Wed, 05 Dec 2012 09:53:07 UTC",
            "_created": "Wed, 05 Dec 2012 09:53:07 UTC",
            "_etag": "ec5e8200b8fa0596afe9ca71a87f23e71ca30e2d",
            "_links": {
                "self": {"href": "eve-demo.herokuapp.com/people/50bf198338345b1c604faf31", "title": "person"},
            },
        },
        {
            "firstname": "Anne",
            "_updated": "Wed, 05 Dec 2012 09:53:07 UTC",
            ...
        } ,
        ...
    ],
    "_links": {
        "self": {"href": "eve-demo.herokuapp.com/people", "title": "people"},
        "parent": {"href": "eve-demo.herokuapp.com", "title": "home"}
    }
}

The _items list contains the requested data. Along with its own fields, each item provides some important, additional fields:

Field	Description
`_created`	item creation date.
`_updated`	item last updated on.
`_etag`	ETag, to be used for concurrency control and conditional requests.
`_id`	unique item key, also needed to access the indivdual item endpoint.

These additional fields are automatically handled by the API (clients don't need to provide them when adding/editing resources).

Conditional requests

In the above response, a Last-Modified header is included. It can be used later to retrieve only the items that have changed since:

$ curl -H "If-Modified-Since: Wed, 05 Dec 2012 09:53:07 UTC" -i http://eve-demo.herokuapp.com:5000/people/

Response:

HTTP/1.0 200 OK
...

{
    "_items": [],
    "_links": [..]
}

This time we didn't get any item back as none has changed since the previous request.

Filtering and sorting

Eve-powered APIs support several kinds of conditional requests. Besides the If-Modified-Since header, you can also submit queries. There are two supported query syntaxes, the MongoDB query syntax:

$ curl -i http://eve-demo.herokuapp.com/people?where={"lastname": "Doe"}

and the native Python syntax:

$ curl -i http://eve-demo.herokuapp.com/people?where=lastname=="Doe"

Sorting is supported as well:

$ curl -i http://eve-demo.herokuapp.com/people?sort=[("lastname", -1)]

Currently sort directives use a pure MongoDB syntax; support for a more general syntax (sort=lastname) is planned.

Pagination

In order to save bandwith and resources, pagination is enabled by default. You have control on the default page size and the maximum number of items per page.

$ curl -i http://eve-demo.herokuapp.com/people?max_results=20&page=2

Of course you can mix all the available query parameters:

$ curl -i http://eve-demo.herokuapp.com/people/?where={"lastaname": "Doe"}&sort=[("firstname",1)]&page=5

Multiple inserts

Insertion is done at the resource endpoint via POST. Multiple items can be inserted with a single request.

$ curl -d '[{"firstname": "barack", "lastname": "obama"}, {"firstname": "mitt", "lastname": "romney"}]' -H 'Content-Type: application/json' http://eve-demo.herokuapp.com/people

Response:

{
    [
        "_status": "OK",
        "_updated": "Thu, 22 Nov 2012 15:22:27 UTC",
        "_id": "50ae43339fa12500024def5b",
        "_links": {"self": {"href": "eve-demo.herokuapp.com/people/50ae43339fa12500024def5b", "title": "person"}}
    ],
    [
        "_status": "OK",
        "_updated": "Thu, 22 Nov 2012 15:22:27 UTC",
        "_id": "50ae43339fa12500024def5c",
        "_links": {"self": {"href": "eve-demo.herokuapp.com/people/50ae43339fa12500024def5c", "title": "person"}}
    ]
}

The response will contain a status update for each item inserted. If the insertion succeeded, item status will include the update/creation date, the new unique id and a link to the item endpoint.

The API mantainer controls wether insertion is allowed. By default, APIs are read-only.

Data validation

An item won't be inserted if it doesn't validate against the validation rules set by the API maintainer. The whole the request is always processed, which means that eventual validation errors won't prevent insertion of valid items.

$ curl -d '[{"firstname": "bill", "lastname": "clinton"}, {"firstname": "mitt", "lastname": "romney"}]' -H 'Content-Type: application/json' http://eve-demo.herokuapp.com/people

Response:

[
    {
        "_status": "ERR",
        "_issues": {"lastname": "value 'clinton' not unique"}
    },
    {
        "_status": "OK",
        "_updated": "Thu, 22 Nov 2012 15:29:08 GMT",
        "_id": "50ae44c49fa12500024def5d",
        "_links": {"self": {"href": "eve-demo.herokuapp.com/people/50ae44c49fa12500024def5d", "title": "person"}}
    }
]

In the above example, the first document did not validate and was rejected, while the second document was successfully created. API maintainer has complete control on data validation. Since Eve validation is based on Cerberus, it is also possible to extend the system to suit specific use cases. Check out the settings.py module used in this demo to get an idea of how data structures are configured.

Resource Deletion

If enabled by the maintainer, an Eve-powered API will also allow deletion of the whole content of a resource.

$ curl -X DELETE http://eve-demo.herokuapp.com/people

Again, Eve-powered APIs are read-only by default. Enabling/disabling features is just a matter of setting the appropriate value in the configuration module.

Item Endpoints

Item endpoints are accessed by combining parent resource URI and item unique key.

$ curl -i http://eve-demo.herokuapp.com/people/50acfba938345b0978fccad7

If enabled by the API mantainer, it is also possibile to access the same item with a secondary field value (in our case, lastname):

$ curl -i http://eve-demo.herokuapp.com/people/Doe

Response:

HTTP/1.0 200 OK
Etag: 28995829ee85d69c4c18d597a0f68ae606a266cc
Last-Modified: Wed, 21 Nov 2012 16:04:56 UTC
...

{
    "firstname": "John",
    "lastname": "Doe",
    "born": "Thu, 27 Aug 1970 14:37:13 UTC",
    "role": ["author"],
    "location": {"city": "Auburn", "address": "422 South Gay Street"},
    "_id": "50acfba938345b0978fccad7"
    "_updated": "Wed, 21 Nov 2012 16:04:56 UTC",
    "_created": "Wed, 21 Nov 2012 16:04:56 UTC",
    "_links": {
        "self": {"href": "eve-demo.herokuapp.com/people/50acfba938345b0978fccad7", "title": "person"},
        "parent": {"href": "eve-demo.herokuapp.com", "title": "home"},
        "collection": {"href": "//eve-demo.herokuapp.com/people", "title": "people"}
    }
}

Editing and deleting items

Concurrency Control

The header provided with the above response contains an ETag which is very important because etags are mandatory for performing edit and delete operations on items. Editing happens at the item endpoint and is allowed only if the request includes an ETag that matches the current representation stored on the server. This prevents overwriting the items with obsolete versions.

$ curl -X PATCH -i http://eve-demo.herokuapp.com/people/521d6840c437dc0002d1203c -d '{"firstname": "ronald"}'

HTTP/1.0 403 FORBIDDEN

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<title>403 Forbidden</title>
<h1>Forbidden</h1>
<p>You don't have the permission to access the requested resource. It is either read-protected or not readable by the server.</p>

We did not provide an ETag for the item so we got a not-so-nice 403 FORBIDDEN. Let's try again:

$ curl -H "If-Match: 1234567890123456789012345678901234567890" -X PATCH -i http://eve-demo.herokuapp.com/people/521d6840c437dc0002d1203c -d '{"firstname": "ronald"}'

HTTP/1.0 412 PRECONDITION FAILED

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<title>412 Precondition Failed</title>
<h1>Precondition Failed</h1>

What went wrong this time? We did provide the mandatory If-Match header, but it did not match the ETag computed on the representation of the current item, so we got a 402 PRECONDITION FAILED. Again!

$ curl -H "If-Match: 80b81f314712932a4d4ea75ab0b76a4eea613012" -X PATCH -i http://eve-demo.herokuapp.com/people/50adfa4038345b1049c88a37 -d '{"firstname": "ronald"}'

Response:

HTTP/1.0 200 OK
ETag: 372fbbebf54dfe61742556f17a8461ca9a6f5a11
Last-Modified: Fri, 23 Nov 2012 08:11:19 UTC
...

{
    "_status": "OK",
    "_updated": "Fri, 23 Nov 2012 08:11:19 GMT",
    "_id": "50adfa4038345b1049c88a37",
    "_etag": "372fbbebf54dfe61742556f17a8461ca9a6f5a11"
    "_links": {"self": "..."}
}

This time we got our patch in, and the server returned the new ETag. We also get the new updated value, which eventually will allow us to perform subsequent If-Modified-Since requests.

Local install

If you want to play with this app locally create a virtualenv environment and once activated install Eve:

$ pip install eve

Then, just clone this repository:

$ git clone https://github.com/nicolaiarocci/eve-demo.git

Of course you need a local instance of MongoDB running, and don't forget to ajust the settings.py module accordingly. Launching the API is straightforward:

$ python run.py

Have fun!

Wrapping it up

Check out the settings.py module used in this demo to get an idea of how configuration is handled. Also don't forget to visit Eve website and, if you need a gentle introduction to the wondeful world of RESTful WEB APIs, check out my EuroPython 2012 talk: Developing RESTful Web APIs with Python, Flask and MongoDB - thank you.

careychow/eve-demo

Eve-Demo

Try it live

API Entry Point

Cache Control

JSON and XML rendering

Resource Endpoints

Conditional requests

Filtering and sorting

Pagination

Multiple inserts

Data validation

Resource Deletion

Item Endpoints

Editing and deleting items

Concurrency Control

Local install

Wrapping it up