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86 lines
2.5 KiB
ReStructuredText
86 lines
2.5 KiB
ReStructuredText
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Nodes
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=====
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A ``Node`` is an Interface provided by ``graphene.relay`` that contains
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a single field ``id`` (which is a ``ID!``). Any object that inherits
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from it have to implement a ``get_node`` method for retrieving a
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``Node`` by an *id*.
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Quick example
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-------------
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Example usage (taken from the `Starwars Relay example`_):
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.. code:: python
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class Ship(graphene.ObjectType):
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'''A ship in the Star Wars saga'''
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class Meta:
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interfaces = (relay.Node, )
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name = graphene.String(description='The name of the ship.')
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@classmethod
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def get_node(cls, id, context, info):
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return get_ship(id)
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The ``id`` returned by the ``Ship`` type when you query it will be a
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scalar which contains the enough info for the server for knowing it’s
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type and it’s id.
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For example, the instance ``Ship(id=1)`` will return ``U2hpcDox`` as the
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id when you query it (which is the base64 encoding of ``Ship:1``), and
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which could be useful later if we want to query a node by its id.
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Custom Nodes
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------------
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You can use the predefined ``relay.Node`` or you can subclass it, defining
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custom ways of how a node id is encoded (using the ``to_global_id`` method in the class)
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or how we can retrieve a Node given a encoded id (with the ``get_node_from_global_id`` method).
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Example of a custom node:
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.. code:: python
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class CustomNode(Node):
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class Meta:
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name = 'Node'
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@staticmethod
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def to_global_id(type, id):
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return '{}:{}'.format(type, id)
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@staticmethod
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def get_node_from_global_id(global_id, context, info):
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type, id = global_id.split(':')
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if type == 'User':
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return get_user(id)
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elif type == 'Photo':
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return get_photo(id)
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The ``get_node_from_global_id`` method will be called when ``CustomNode.Field`` is resolved.
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Node Root field
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---------------
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As is required in the `Relay specification`_, the server must implement
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a root field called ``node`` that returns a ``Node`` Interface.
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For this reason, ``graphene`` provides the field ``relay.Node.Field``,
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which links to any type in the Schema which implements ``Node``.
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Example usage:
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.. code:: python
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class Query(graphene.ObjectType):
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# Should be CustomNode.Field() if we want to use our custom Node
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node = relay.Node.Field()
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.. _Starwars Relay example: https://github.com/graphql-python/graphene/blob/master/examples/starwars_relay/schema.py
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