Customizing the ReSTful interface¶
HTTP methods¶
By default, the APIManager.create_api()
method creates a read-only
interface; requests with HTTP methods other than GET will cause
a response with 405 Method Not Allowed. To explicitly specify which methods
should be allowed for the endpoint, pass a list as the value of keyword
argument methods
:
apimanager.create_api(Person, methods=['GET', 'POST', 'DELETE'])
This creates an endpoint at /api/person
which responds to
GET, POST, and DELETE methods, but
not to other ones like PUT or PATCH.
The recognized HTTP methods and their semantics are described below (assuming
you have created an API for an entity Person
). All endpoints which respond
with data respond with serialized JSON strings.
-
GET
/api/person
¶ Returns a list of all
Person
instances.
-
GET
/api/person/
(int: id)¶ Returns a single
Person
instance with the givenid
.
-
GET
/api/person?q=<searchjson>
¶ Returns a list of all
Person
instances which match the search query specified in the query parameterq
. For more information on searching, see Making search queries.
-
DELETE
/api/person/
(int: id)¶ Deletes the person with the given
id
and returns 204 No Content.
-
DELETE
/api/person
¶ This is only available if the
allow_delete_many
keyword argument is set toTrue
when calling thecreate_api()
method. For more information, see Enable bulk patching or deleting.Deletes all instances of
Person
that match the search query provided in theq
URL query paremeter. For more information on search parameters, see Making search queries.
-
POST
/api/person
¶ Creates a new person in the database and returns its
id
. The initial attributes of thePerson
are read as JSON from the body of the request. For information about the format of this request, see Format of requests and responses.
-
PATCH
/api/person/
(int: id)¶ Updates the attributes of the
Person
with the givenid
. The attributes are read as JSON from the body of the request. For information about the format of this request, see Format of requests and responses.
-
PATCH
/api/person
¶ This is only available if the
allow_patch_many
keyword argument is set toTrue
when calling thecreate_api()
method. For more information, see allowpatchmany.Updates the attributes of all
Person
instances. The attributes are read as JSON from the body of the request. For information about the format of this request, see Format of requests and responses.
-
PUT
/api/person
¶
-
PUT
/api/person/
(int: id)¶ Aliases for
PATCH /api/person
andPATCH /api/person/(int:id)
.
API prefix¶
To create an API at a different prefix, use the url_prefix
keyword
argument:
apimanager.create_api(Person, url_prefix='/api/v2')
Then your API for Person
will be available at /api/v2/person
.
Collection name¶
By default, the name of the collection which appears in the URLs of the API
will be the name of the table that backs your model. If your model is a
SQLAlchemy model, this will be the value of its __tablename__
attribute. If
your model is a Flask-SQLAlchemy model, this will be the lowercase name of the
model with camel case changed to all-lowercase with underscore separators. For
example, a class named MyModel
implies a collection name of
'my_model'
. Furthermore, the URL at which this collection is accessible by
default is /api/my_model
.
To provide a different name for the model, provide a string to the
collection_name keyword argument of the APIManager.create_api()
method:
apimanager.create_api(Person, collection_name='people')
Then the API will be exposed at /api/people
instead of /api/person
.
Specifying one of many primary keys¶
If your model has more than one primary key (one called id
and one called
username
, for example), you should specify the one to use:
manager.create_api(User, primary_key='username')
If you do this, Flask-Restless will create URLs like /api/user/myusername
instead of /api/user/137
.
Enable bulk patching or deleting¶
By default, a PATCH /api/person
request (note the missing ID) will
cause a 405 Method Not Allowed response. By setting the allow_patch_many
keyword argument of the APIManager.create_api()
method to be True
,
PATCH /api/person
requests will patch the provided attributes on all
instances of Person
:
apimanager.create_api(Person, methods=['PATCH'], allow_patch_many=True)
If search parameters are provided via the q
query parameter as described in
Making search queries, only those instances matching the search will be patched.
Similarly, to allow bulk deletions, set the allow_delete_many
keyword
argument to be True
.
Capturing validation errors¶
By default, no validation is performed by Flask-Restless; if you want validation, implement it yourself in your database models. However, by specifying a list of exceptions raised by your backend on validation errors, Flask-Restless will forward messages from raised exceptions to the client in an error response.
A reasonable validation framework you might use for this purpose is SQLAlchemy
Validation. You can
also use the validates()
decorator that comes with
SQLAlchemy.
For example, if your validation framework includes an exception called
ValidationError
, then call the APIManager.create_api()
method with
the validation_exceptions
keyword argument:
from cool_validation_framework import ValidationError
apimanager.create_api(Person, validation_exceptions=[ValidationError])
Note
Currently, Flask-Restless expects that an instance of a specified validation
error will have a errors
attribute, which is a dictionary mapping field
name to error description (note: one error per field). If you have a better,
more general solution to this problem, please visit our issue tracker.
Now when you make POST and PATCH requests with invalid fields, the JSON response will look like this:
HTTP/1.1 400 Bad Request
{ "validation_errors":
{
"age": "Must be an integer",
}
}
Currently, Flask-Restless can only forward one exception at a time to the client.
Exposing evaluation of SQL functions¶
If the allow_functions
keyword argument is set to True
when creating an
API for a model using APIManager.create_api()
, then an endpoint will be
made available for GET /api/eval/person
which responds to requests for
evaluation of functions on all instances the model.
For information about the request and response formats for this endpoint, see Function evaluation.
Specifying which columns are provided in responses¶
By default, all columns of your model will be exposed by the API. If the
include_columns
keyword argument is an iterable of strings, only columns
with those names (that is, the strings represent the names of attributes of the
model which are Column
objects) will be provided in JSON responses for
GET requests.
For example, if your models are defined like this (using Flask-SQLAlchemy):
class Person(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.Unicode, unique=True)
birth_date = db.Column(db.Date)
computers = db.relationship('Computer')
and you want your JSON responses to include only the values of the name
and
birth_date
columns, create your API with the following arguments:
apimanager.create_api(Person, include_columns=['name', 'birth_date'])
Now requests like GET /api/person/1
will return JSON objects which look
like this:
{"name": "Jeffrey", "birth_date": "1999-12-31"}
The exclude_columns
keyword argument works similarly; it forces your JSON
responses to include only the columns not specified in exclude_columns
.
For example:
apimanager.create_api(Person, exclude_columns=['name', 'birth_date'])
will produce responses like:
{"id": 1, "computers": [{"id": 1, "vendor": "Apple", "model": "MacBook"}]}
In this example, the Person
model has a one-to-many relationship with the
Computer
model. To specify which columns on the related models will be
included or excluded, include a string of the form '<relation>.<column>'
,
where <relation>
is the name of the relationship attribute of the model and
<column>
is the name of the column on the related model which you want to
be included or excluded. For example:
includes = ['name', 'birth_date', 'computers', 'computers.vendor']
apimanager.create_api(Person, include_columns=includes)
will produce responses like:
{
"name": "Jeffrey",
"birth_date": "1999-12-31",
"computers": [{"vendor": "Apple"}]
}
An attempt to include a field on a related model without including the relationship field has no effect:
includes = ['name', 'birth_date', 'computers.vendor']
apimanager.create_api(Person, include_columns=includes)
{"name": "Jeffrey", "birth_date": "1999-12-31"}
To include the return value of an arbitrary method defined on a model, use the
include_methods
keyword argument. This argument must be an iterable of
strings representing methods with no arguments (other than self
) defined on
the model for which the API will be created:
class Person(Base):
__tablename__ = 'person'
id = Column(Integer, primary_key=True)
name = Column(Unicode)
age = Column(Integer)
def name_and_age(self):
return "%s (aged %d)" % (self.name, self.age)
include_methods = ['name_and_age']
manager.create_api(Person, include_methods=['name_and_age'])
A response to a GET request will then look like this:
{
"id": 1,
"name": "Paul McCartney",
"age": 64,
"name_and_age": "Paul McCartney (aged 64)"
}
Server-side pagination¶
To set the default number of results returned per page, use the
results_per_page
keyword argument to the APIManager.create_api()
method. The default number of results per page is ten. The client can override
the number of results per page by using a query parameter in its
GET request; see Pagination.
To set the maximum number of results returned per page, use the
max_results_per_page
keyword argument. Even if results_per_page >
max_results_per_page
, at most max_results_per_page
will be returned. The
same is true if the client specifies results_per_page
as a query argument;
max_results_per_page
provides an upper bound.
If max_results_per_page
is set to anything but a positive integer, the
client will be able to specify arbitrarily large page sizes. If, further,
results_per_page
is set to anything but a positive integer, pagination will
be disabled by default, and any GET request which does not
specify a page size in its query parameters will get a response with all
matching results.
Attention
Disabling pagination can result in large responses!
For example, to set each page to include only two results:
apimanager.create_api(Person, results_per_page=2)
Then a request to GET /api/person
will return a JSON object which looks
like this:
{
"num_results": 6,
"total_pages": 3,
"page": 1,
"objects": [
{"name": "Jeffrey", "id": 1},
{"name": "John", "id": 2}
]
}
For more information on using pagination in the client, see Pagination.
Request preprocessors and postprocessors¶
To apply a function to the request parameters and/or body before the request is
processed, use the preprocessors
keyword argument. To apply a function to
the response data after the request is processed (immediately before the
response is sent), use the postprocessors
keyword argument. Both
preprocessors
and postprocessors
must be a dictionary which maps HTTP
method names as strings (with exceptions as described below) to a list of
functions. The specified functions will be applied in the order given in the
list.
Since GET and PATCH (and PUT) requests can be made not only on individual instances of the model but also the entire collection of instances, you must separately specify which functions to apply in the individual case and which to apply in the collection case. For example:
# Define pre- and postprocessor functions as described below.
def pre_get_single(**kw): pass
def pre_get_many(**kw): pass
def post_patch_many(**kw): pass
def pre_delete(**kw): pass
# Create an API for the Person model.
manager.create_api(Person,
# Allow GET, PATCH, and POST requests.
methods=['GET', 'PATCH', 'DELETE'],
# Allow PATCH requests modifying the whole collection.
allow_patch_many=True,
# A list of preprocessors for each method.
preprocessors={
'GET_SINGLE': [pre_get_single],
'GET_MANY': [pre_get_many],
'DELETE': [pre_delete]
},
# A list of postprocessors for each method.
postprocessors={
'PATCH_MANY': [post_patch_many]
}
)
As introduced in the above example, the dictionary keys for the preprocessors and postprocessors can be one of the following strings:
'POST'
for requests to post a new instance of the model.'GET_SINGLE'
for requests to get a single instance of the model.'GET_MANY'
for requests to get multiple instances of the model.'PATCH_SINGLE'
or'PUT_SINGLE'
for requests to patch a single instance of the model.'PATCH_MANY'
or'PUT_MANY'
for requests to patch multiple instances of the model.'DELETE_SINGLE'
for requests to delete an instance of the model.'DELETE_MANY'
for requests to delete multiple instances of the model.
Note
Since PUT requests are handled by the PATCH handler, any preprocessors or postprocessors specified for the PUT method will be applied on PATCH requests after the preprocessors or postprocessors specified for the PATCH method.
The preprocessors and postprocessors for each type of request accept different
arguments. Most of them should have no return value (more specifically, any
returned value is ignored). The return value from each of the GET_SINGLE
,
PATCH_SINGLE
, and DELETE_SINGLE
preprocessors is interpreted as a value
with which to replace instance_id
, the variable containing the value of the
primary key of the requested instance of the model. For example, if a request
for GET /api/person/1
encounters a preprocessor (for GET_SINGLE
)
that returns the integer 8
, Flask-Restless will continue to process the
request as if it had received GET /api/person/8
. (If multiple
preprocessors are specified for a single HTTP method and each one has a return
value, Flask-Restless will only remember the value returned by the last
preprocessor function.)
Those preprocessors and postprocessors that accept dictionaries as parameters
can (and should) modify their arguments in-place. That means the changes made
to, for example, the result
dictionary will be seen by the Flask-Restless
view functions and ultimately returned to the client.
The arguments to the preprocessor and postprocessor functions will be provided
as keyword arguments, so you should always add **kw
as the final argument
when defining a preprocessor or postprocessor function. This way, you can
specify only the keyword arguments you need when defining your
functions. Furthermore, if a new version of Flask-Restless changes the API,
you can update Flask-Restless without breaking your code.
Changed in version 0.16.0: Replaced DELETE
with DELETE_MANY
and DELETE_SINGLE
.
New in version 0.13.0: Functions provided as postprocessors for GET_MANY
and PATCH_MANY
requests receive the search_params
keyword argument, so that both
preprocessors and postprocessors have access to this information.
GET for a single instance:
def get_single_preprocessor(instance_id=None, **kw): """Accepts a single argument, `instance_id`, the primary key of the instance of the model to get. """ pass def get_single_postprocessor(result=None, **kw): """Accepts a single argument, `result`, which is the dictionary representation of the requested instance of the model. """ pass
and for the collection:
def get_many_preprocessor(search_params=None, **kw): """Accepts a single argument, `search_params`, which is a dictionary containing the search parameters for the request. """ pass def get_many_postprocessor(result=None, search_params=None, **kw): """Accepts two arguments, `result`, which is the dictionary representation of the JSON response which will be returned to the client, and `search_params`, which is a dictionary containing the search parameters for the request (that produced the specified `result`). """ pass
PATCH (or PUT) for a single instance:
def patch_single_preprocessor(instance_id=None, data=None, **kw): """Accepts two arguments, `instance_id`, the primary key of the instance of the model to patch, and `data`, the dictionary of fields to change on the instance. """ pass def patch_single_postprocessor(result=None, **kw): """Accepts a single argument, `result`, which is the dictionary representation of the requested instance of the model. """ pass
and for the collection:
def patch_many_preprocessor(search_params=None, data=None, **kw): """Accepts two arguments: `search_params`, which is a dictionary containing the search parameters for the request, and `data`, which is a dictionary representing the fields to change on the matching instances and the values to which they will be set. """ pass def patch_many_postprocessor(query=None, data=None, search_params=None, **kw): """Accepts three arguments: `query`, which is the SQLAlchemy query which was inferred from the search parameters in the query string, `data`, which is the dictionary representation of the JSON response which will be returned to the client, and `search_params`, which is a dictionary containing the search parameters for the request. """ pass
POST:
def post_preprocessor(data=None, **kw): """Accepts a single argument, `data`, which is the dictionary of fields to set on the new instance of the model. """ pass def post_postprocessor(result=None, **kw): """Accepts a single argument, `result`, which is the dictionary representation of the created instance of the model. """ pass
DELETE for a single instance:
def delete_single_preprocessor(instance_id=None, **kw): """Accepts a single argument, `instance_id`, which is the primary key of the instance which will be deleted. """ pass def delete_postprocessor(was_deleted=None, **kw): """Accepts a single argument, `was_deleted`, which represents whether the instance has been deleted. """ pass
and for the collection:
def delete_many_preprocessor(search_params=None, **kw): """Accepts a single argument, `search_params`, which is a dictionary containing the search parameters for the request. """ pass def delete_many_postprocessor(result=None, search_params=None, **kw): """Accepts two arguments: `result`, which is the dictionary representation of which is the dictionary representation of the JSON response which will be returned to the client, and `search_params`, which is a dictionary containing the search parameters for the request. """ pass
Note
For more information about search parameters, see Making search queries, and for more information about request and response formats, see Format of requests and responses.
In order to halt the preprocessing or postprocessing and return an error
response directly to the client, your preprocessor or postprocessor functions
can raise a ProcessingException
. If a function raises this exception, no
preprocessing or postprocessing functions that appear later in the list
specified when the API was created will be invoked. For example, an
authentication function can be implemented like this:
def check_auth(instance_id=None, **kw):
# Here, get the current user from the session.
current_user = ...
# Next, check if the user is authorized to modify the specified
# instance of the model.
if not is_authorized_to_modify(current_user, instance_id):
raise ProcessingException(description='Not Authorized',
code=401)
manager.create_api(Person, preprocessors=dict(GET_SINGLE=[check_auth]))
The ProcessingException
allows you to specify an HTTP status code for
the generated response and an error message which the client will receive as
part of the JSON in the body of the response.
Universal preprocessors and postprocessors¶
New in version 0.13.0.
The previous section describes how to specify a preprocessor or postprocessor
on a per-API (that is, a per-model) basis. If you want a function to be
executed for all APIs created by a APIManager
, you can use the
preprocessors
or postprocessors
keyword arguments in the constructor of
the APIManager
class. These keyword arguments have the same format as
the corresponding ones in the APIManager.create_api()
method as described
above. Functions specified in this way are prepended to the list of
preprocessors or postprocessors specified in the APIManager.create_api()
method.
This may be used, for example, if all POST requests require authentication:
from flask import Flask
from flask.ext.restless import APIManager
from flask.ext.restless import ProcessingException
from flask.ext.login import current_user
from mymodels import User
from mymodels import session
def auth_func(*args, **kw):
if not current_user.is_authenticated():
raise ProcessingException(description='Not authenticated!', code=401)
app = Flask(__name__)
api_manager = APIManager(app, session=session,
preprocessors=dict(POST=[auth_func]))
api_manager.create_api(User)
Preprocessors for collections¶
When the server receives, for example, a request for GET /api/person
,
Flask-Restless interprets this request as a search with no filters (that is, a
search for all instances of Person
without exception). In other words,
GET /api/person
is roughly equivalent to
GET /api/person?q={}
. Therefore, if you want to filter the set of
Person
instances returned by such a request, you can create a preprocessor
for a GET request to the collection endpoint that appends
filters to the search_params
keyword argument. For example:
def preprocessor(search_params=None, **kw):
# This checks if the preprocessor function is being called before a
# request that does not have search parameters.
if search_params is None:
return
# Create the filter you wish to add; in this case, we include only
# instances with ``id`` not equal to 1.
filt = dict(name='id', op='neq', val=1)
# Check if there are any filters there already.
if 'filters' not in search_params:
search_params['filters'] = []
# *Append* your filter to the list of filters.
search_params['filters'].append(filt)
apimanager.create_api(Person, preprocessors=dict(GET_MANY=[preprocessor]))
Custom queries¶
In cases where it is not possible to use preprocessors or postprocessors
(Request preprocessors and postprocessors) efficiently, you can provide a custom query
attribute
to your model instead. The attribute can either be a SQLAlchemy query
expression or a class method that returns a SQLAlchemy query
expression. Flask-Restless will use this query
attribute internally,
however it is defined, instead of the default session.query(Model)
(in the
pure SQLAlchemy case) or Model.query
(in the Flask-SQLAlchemy
case). Flask-Restless uses a query during most GET and
PATCH requests to find the model(s) being requested.
You may want to use a custom query attribute if you want to reveal only certain information to the client. For example, if you have a set of people and you only want to reveal information about people from the group named “students”, define a query class method this way:
class Group(Base):
__tablename__ = 'group'
id = Column(Integer, primary_key=True)
groupname = Column(Unicode)
people = relationship('Person')
class Person(Base):
__tablename__ = 'person'
id = Column(Integer, primary_key=True)
group_id = Column(Integer, ForeignKey('group.id'))
group = relationship('Group')
@classmethod
def query(cls):
original_query = session.query(cls)
condition = (Group.groupname == 'students')
return original_query.join(Group).filter(condition)
Then requests to, for example, GET /api/person
will only reveal
instances of Person
who also are in the group named “students”.
Requiring authentication for some methods¶
If you want certain HTTP methods to require authentication, use preprocessors:
from flask import Flask
from flask.ext.restless import APIManager
from flask.ext.restless import NO_CHANGE
from flask.ext.restless import ProcessingException
from flask.ext.login import current_user
from mymodels import User
def auth_func(*args, **kwargs):
if not current_user.is_authenticated():
raise ProcessingException(description='Not authenticated!', code=401)
return True
app = Flask(__name__)
api_manager = APIManager(app)
api_manager.create_api(User, preprocessors=dict(GET_SINGLE=[auth_func],
GET_MANY=[auth_func]))
For a more complete example using Flask-Login, see the
examples/server_configurations/authentication
directory in the source
distribution, or view it online at GitHub.
Enabling Cross-Origin Resource Sharing (CORS)¶
Cross-Origin Resource Sharing (CORS) is a protocol
that allows JavaScript HTTP clients to make HTTP requests across Internet
domain boundaries while still protecting against cross-site scripting (XSS)
attacks. If you have access to the HTTP server that serves your Flask
application, I recommend configuring CORS there, since such concerns are beyond
the scope of Flask-Restless. However, in case you need to support CORS at the
application level, you should create a function that adds the necessary HTTP
headers after the request has been processed by Flask-Restless (that is, just
before the HTTP response is sent from the server to the client) using the
flask.Blueprint.after_request()
method:
from flask import Flask
from flask.ext.restless import APIManager
def add_cors_headers(response):
response.headers['Access-Control-Allow-Origin'] = 'example.com'
response.headers['Access-Control-Allow-Credentials'] = 'true'
# Set whatever other headers you like...
return response
app = Flask(__name__)
manager = APIManager(app)
blueprint = manager.create_api(Person)
blueprint.after_request(add_cors_headers)