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72 lines
1.9 KiB
ReStructuredText
72 lines
1.9 KiB
ReStructuredText
Middleware
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==========
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You can use ``middleware`` to affect the evaluation of fields in your schema.
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A middleware is any object or function that responds to ``resolve(next_middleware, *args)``.
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Inside that method, it should either:
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- Send ``resolve`` to the next middleware to continue the evaluation; or
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- Return a value to end the evaluation early.
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Resolve arguments
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-----------------
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Middlewares ``resolve`` is invoked with several arguments:
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- ``next`` represents the execution chain. Call ``next`` to continue evaluation.
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- ``root`` is the root value object passed throughout the query.
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- ``info`` is the resolver info.
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- ``args`` is the dict of arguments passed to the field.
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Example
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-------
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This middleware only continues evaluation if the ``field_name`` is not ``'user'``
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.. code:: python
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class AuthorizationMiddleware(object):
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def resolve(next, root, info, **args):
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if info.field_name == 'user':
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return None
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return next(root, info, **args)
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And then execute it with:
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.. code:: python
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result = schema.execute('THE QUERY', middleware=[AuthorizationMiddleware()])
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Functional example
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------------------
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Middleware can also be defined as a function. Here we define a middleware that
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logs the time it takes to resolve each field
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.. code:: python
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from time import time as timer
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def timing_middleware(next, root, info, **args):
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start = timer()
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return_value = next(root, info, **args)
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duration = timer() - start
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logger.debug("{parent_type}.{field_name}: {duration} ms".format(
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parent_type=root._meta.name if root and hasattr(root, '_meta') else '',
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field_name=info.field_name,
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duration=round(duration * 1000, 2)
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))
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return return_value
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And then execute it with:
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.. code:: python
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result = schema.execute('THE QUERY', middleware=[timing_middleware])
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