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161 lines
4.1 KiB
ReStructuredText
161 lines
4.1 KiB
ReStructuredText
ObjectTypes
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===========
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An ObjectType is the single, definitive source of information about your
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data. It contains the essential fields and behaviors of the data you’re
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querying.
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The basics:
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- Each ObjectType is a Python class that inherits
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``graphene.ObjectType``.
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- Each attribute of the ObjectType represents a ``Field``.
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Quick example
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-------------
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This example model defines a Person, which has a first\_name and
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last\_name:
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.. code:: python
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import graphene
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class Person(graphene.ObjectType):
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first_name = graphene.String()
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last_name = graphene.String()
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full_name = graphene.String()
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def resolve_full_name(self, args, context, info):
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return '{} {}'.format(self.first_name, self.last_name)
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**first\_name** and **last\_name** are fields of the ObjectType. Each
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field is specified as a class attribute, and each attribute maps to a
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Field.
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The above ``Person`` ObjectType would have the following representation
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in a schema:
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.. code::
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type Person {
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firstName: String
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lastName: String
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fullName: String
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}
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Resolvers
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---------
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A resolver is a method that resolves certain field within a
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``ObjectType``. The resolver of a field will be, if not specified
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otherwise, the ``resolve_{field_name}`` within the ``ObjectType``.
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By default a resolver will take the ``args``, ``context`` and ``info``
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arguments.
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NOTE: The class resolvers in a ``ObjectType`` are treated as ``staticmethod``s
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always, so the first argument in the resolver: ``self`` (or ``root``) doesn't
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need to be an actual instance of the ``ObjectType``. In the case this happens, please
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overwrite the ``is_type_of`` method.
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Quick example
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~~~~~~~~~~~~~
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This example model defines a ``Query`` type, which has a reverse field
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that reverses the given ``word`` argument using the ``resolve_reverse``
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method in the class.
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.. code:: python
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import graphene
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class Query(graphene.ObjectType):
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reverse = graphene.String(word=graphene.String())
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def resolve_reverse(self, args, context, info):
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word = args.get('word')
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return word[::-1]
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Resolvers outside the class
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~~~~~~~~~~~~~~~~~~~~~~~~~~~
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A field could also specify a custom resolver outside the class:
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.. code:: python
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import graphene
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def reverse(root, args, context, info):
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word = args.get('word')
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return word[::-1]
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class Query(graphene.ObjectType):
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reverse = graphene.String(word=graphene.String(), resolver=reverse)
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Is Type Of
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----------
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An ``ObjectType`` could be resolved within a object that is not an instance of this
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``ObjectType``. That means that the resolver of a ``Field`` could return any object.
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Let's see an example:
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.. code:: python
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import graphene
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class Ship:
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def __init__(self, name):
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self.name = name
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class ShipType(graphene.ObjectType):
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name = graphene.String(description="Ship name", required=True)
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@resolve_only_args
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def resolve_name(self):
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# Here self will be the Ship instance returned in resolve_ship
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return self.name
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class Query(graphene.ObjectType):
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ship = graphene.Field(ShipType)
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def resolve_ship(self, context, args, info):
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return Ship(name='xwing')
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schema = graphene.Schema(query=Query)
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In this example, we are returning a ``Ship`` which is not an instance of ``ShipType``.
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If we execute a query on the ship, we would see this error:
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`"Expected value of type \"ShipType\" but got: instance."`
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That's happening because GraphQL have no idea what type ``Ship`` is. For solving this,
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we only have to add a ``is_type_of`` method in ``ShipType``
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.. code:: python
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class ShipType(graphene.ObjectType):
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@classmethod
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def is_type_of(cls, root, context, info):
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return isinstance(root, (Ship, ShipType))
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Instances as data containers
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----------------------------
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Graphene ``ObjectType``\ s could act as containers too. So with the
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previous example you could do.
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.. code:: python
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peter = Person(first_name='Peter', last_name='Griffin')
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peter.first_name # prints "Peter"
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peter.last_name # prints "Griffin"
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.. _Interface: /docs/interfaces/
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