How to extend the AiiDA REST API¶
The AiIDA REST API is made of two main classes:
App
, inheritingflask.Flask
. The latter represents any Flask web app, including REST APIs.
Api
, inheritingflask_restful.Api
. This represents the API itself.
Once instanciated both Api
and App
classes into, say, app
and api
,
these two objects have to be coupled by adding app
as one of the attributes of api
.
As we will see in a moment, we provide a function that, besides other things, does exactly this.
In a Flask API the resources, e.g. Nodes, ProcessNodes,
etc., are represented by flask_restful.Resource
-derived classes.
If you need to include additional endpoints besides those built in the AiiDA REST API you should:
create the resource classes that will be bound to the new endpoints;
extend the class
Api
into a user-defined class to register the new endpoints.(Optional) Extend
App
into a user-defined class for finer customization.
Let’s provide a minimal example through which we add the endpoint
/new-endpoint
supporting two HTTP methods:
GET: retrieves the latest created Dict object and returns its
id
,ctime
in ISO 8601 format, andattributes
.POST: creates a
Dict
object with placeholder attributes, stores it, and returns itsid
.
Let’s assume you’ve put the code in the file example.py
, reading:
#!/usr/bin/env python
from aiida.restapi.api import AiidaApi, App
from aiida.restapi.run_api import run_api
from flask_restful import Resource
class NewResource(Resource):
"""
resource containing GET and POST methods. Description of each method
follows:
GET: returns id, ctime, and attributes of the latest created Dict.
POST: creates a Dict object, stores it in the database,
and returns its newly assigned id.
"""
def get(self):
from aiida.orm import QueryBuilder, Dict
qb = QueryBuilder()
qb.append(Dict,
project=['id', 'ctime', 'attributes'],
tag='pdata')
qb.order_by({'pdata': {'ctime': "desc"}})
result = qb.first()
# Results are returned as a dictionary, datetime objects is
# serialized as ISO 8601
return dict(id=result[0],
ctime=result[1].isoformat(),
attributes=result[2])
def post(self):
from aiida.orm import Dict
params = dict(property1="spam", property2="egg")
paramsData = Dict(dict=params).store()
return {'id': paramsData.pk}
class NewApi(AiidaApi):
def __init__(self, app=None, **kwargs):
"""
This init serves to add new endpoints to the basic AiiDA Api
"""
super().__init__(app=app, **kwargs)
self.add_resource(NewResource, '/new-endpoint/', strict_slashes=False)
# processing the options and running the app
import aiida.restapi.common as common
from aiida import load_profile
CONFIG_DIR = common.__path__[0]
import click
@click.command()
@click.option('-P', '--port', type=click.INT, default=5000,
help='Port number')
@click.option('-H', '--hostname', default='127.0.0.1',
help='Hostname')
@click.option('-c','--config-dir','config',type=click.Path(exists=True), default=CONFIG_DIR,
help='the path of the configuration directory')
@click.option('--debug', 'debug', is_flag=True, default=False,
help='run app in debug mode')
@click.option('--wsgi-profile', 'wsgi_profile', is_flag=True, default=False,
help='to use WSGI profiler middleware for finding bottlenecks in web application')
def newendpoint(**kwargs):
"""
runs the REST api
"""
# Invoke the runner
run_api(App, NewApi, **kwargs)
# main program
if __name__ == '__main__':
"""
Run the app with the provided options. For example:
python example.py --hostname=127.0.0.2 --port=6000
"""
load_profile()
newendpoint()
Let us dissect the previous code explaining each part. First things first: the imports.
from aiida.restapi.api import AiidaApi, App
from aiida.restapi.run_api import run_api
from flask_restful import Resource
To start with, we import the base classes to be extended/employed: AiidaApi
and App
.
For simplicity, it is advisable to import the method run_api
, as it provides an interface
to configure the Api, parse command-line arguments, and couple the two classes representing the Api
and the App. However, you can refer to the documentation of
flask_restful to configure and hook-up an
Api through its built-in methods.
Then we define a class representing the additional resource:
class NewResource(Resource):
"""
resource containing GET and POST methods. Description of each method
follows:
GET: returns id, ctime, and attributes of the latest created Dict.
POST: creates a Dict object, stores it in the database,
and returns its newly assigned id.
"""
def get(self):
from aiida.orm import QueryBuilder, Dict
qb = QueryBuilder()
qb.append(Dict,
project=['id', 'ctime', 'attributes'],
tag='pdata')
qb.order_by({'pdata': {'ctime': "desc"}})
result = qb.first()
# Results are returned as a dictionary, datetime objects is
# serialized as ISO 8601
return dict(id=result[0],
ctime=result[1].isoformat(),
attributes=result[2])
def post(self):
from aiida.orm import Dict
params = dict(property1="spam", property2="egg")
paramsData = Dict(dict=params).store()
return {'id': paramsData.pk}
The class NewResource
contains two methods: get
and post
.
The names chosen for these functions are not arbitrary but fixed
by Flask
to individuate the functions that respond to HTTP request
of type GET and POST, respectively.
In other words, when the API receives a GET (POST) request to the
URL new-endpoint
, the function NewResource.get()
(NewResource.post()
)
will be executed.
The HTTP response is constructed around the data returned by these functions.
The data, which are packed as dictionaries, are serialized by Flask as a JSON
stream of data. All the Python built-in types can be serialized by Flask
(e.g. int
, float
, str
, etc.), whereas for serialization of custom types
we let you refer to the Flask documentation .
The documentation of Flask is the main source of information also for topics
such as customization of HTTP responses, construction of custom URLs
(e.g. accepting parameters), and more advanced serialization issues.
Whenever you face the need to handle errors, consider to use the AiiDA
REST API-specific exceptions already defined in aiida.restapi.common.exceptions
.
The reason will become clear slightly later in this section.
Once the new resource is defined, we have to register it to the API by assigning
it one (or more) endpoint(s).
This is done in the __init__()
of NewApi
by means of the method add_resource()
:
class NewApi(AiidaApi):
def __init__(self, app=None, **kwargs):
"""
This init serves to add new endpoints to the basic AiiDA Api
"""
super().__init__(app=app, **kwargs)
self.add_resource(NewResource, '/new-endpoint/', strict_slashes=False)
In our original intentions, the main (if not the only) purpose of overriding the
__init__()
method is to register new resources to the API.
In fact, the general form of __init__()
is meant to be:
class NewApi(AiidaApi):
def __init__(self, app=None, **kwargs):
super())
self.add_resource( ... )
self.add_resource( ... )
self.add_resource( ... )
...
In the example, indeed, the only characteristic line is
self.add_resource(NewResource, ‘/new-endpoint/’, strict_slashes=False)
.
Anyway, the method add_resource()
is defined and documented in Flask.
Finally, the main
code configures and runs the API:
import aiida.restapi.common as common
from aiida import load_profile
CONFIG_DIR = common.__path__[0]
import click
@click.command()
@click.option('-P', '--port', type=click.INT, default=5000,
help='Port number')
@click.option('-H', '--hostname', default='127.0.0.1',
help='Hostname')
@click.option('-c','--config-dir','config',type=click.Path(exists=True), default=CONFIG_DIR,
help='the path of the configuration directory')
@click.option('--debug', 'debug', is_flag=True, default=False,
help='run app in debug mode')
@click.option('--wsgi-profile', 'wsgi_profile', is_flag=True, default=False,
help='to use WSGI profiler middleware for finding bottlenecks in web application')
def newendpoint(**kwargs):
"""
runs the REST api
"""
# Invoke the runner
run_api(App, NewApi, **kwargs)
# main program
if __name__ == '__main__':
"""
Run the app with the provided options. For example:
python example.py --host=127.0.0.2 --port=6000
"""
load_profile()
newendpoint()
The click package is used to provide a
a nice command line interface to process the options and handle the default values to
pass to the newendpoint
function.
The method run_api()
accomplishes several functions:
it couples the API to an instance of flask.Flask
, namely, the Flask fundamental
class representing a web app. Consequently, the app is configured and, if required, hooked up.
The spirit of run_api
is to take all the ingredients to setup an API and use them
to build up a command-line utility that serves to hook it up.
It requires as inputs:
the classes representing the Api and the App. We strongly suggest to pass to
run_api()
theaiida.restapi.api.App
class, inheriting fromflask.Flask
, as it handles correctly AiiDA RESTApi-specific exceptions.positional arguments representing the command-line arguments/options, passed by the click function. Types, defaults and help strings can be set in the
@click.option
definitions, and will be handled by the command line call.
You should know few more things before using the script:
If you want to customize further the error handling, you can take inspiration by looking at the definition of
App
and create your derived classNewApp(App)
.the supported command line options are identical to those of
verdi restapi
. Useverdi restapi --help
for their full documentation. If you want to add more options or modify the existing ones, create you custom runner taking inspiration fromrun_api
.
It is time to run example.py
. Type in a terminal
chmod +x example.py
./example.py --host=127.0.0.2 --port=6000
You should read the message
* Running on http://127.0.0.2:6000/ (Press CTRL+C to quit)
To route a request to the API from a terminal you can employ curl
.
Alternatively, you can use any REST client providing a GUI.
Let us first ask for the latest created node through the GET method:
curl http://127.0.0.2:6000/api/v4/new-endpoint/ -X GET
The form of the output (and only the form) should resemble
{
"attributes": {
"binding_energy_per_substructure_per_unit_area_units": "eV/ang^2",
"binding_energy_per_substructure_per_unit_area": 0.0220032273047497
},
"ctime": "2017-04-05T16:01:06.227942+00:00",
"id": 403504
}
whereas the actual values of the response dictionary as well as the internal structure of the attributes field will be in general very different.
Now, let us create a node through the POST method, and check it again through GET:
curl http://127.0.0.2:6000/api/v4/new-endpoint/ -X POST
{"id": 410618}
curl http://127.0.0.2:6000/api/v4/new-endpoint/ -X GET
{
"attributes": {
"property1": "spam",
"property2": "egg"
},
"ctime": "2017-06-20T15:36:56.320180+00:00",
"id": 410618
}
The POST request triggers the creation of a new Dict
node,
as confirmed by the response to the GET request.
As a final remark, there might be circumstances in which you do not want to use the internal werkzeug-based server.
For example, you might want to run the app through Apache using a wsgi script.
In this case, simply use configure_api
to return two custom objects app
and api
:
(app, api) = configure_api(App, MycloudApi, **kwargs)
This snippet of code becomes the fundamental block of a wsgi file used by Apache as documented in How to run the REST API through Apache. Moreover, we recommend to consult the documentation of mod_wsgi.
Note
Optionally, create a click option for the variable catch_internal_server
to be False
in order to let exceptions (including python tracebacks) bubble up to the apache error log.
This can be particularly useful when the app is still under heavy development.