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35 lines
1.2 KiB
ReStructuredText
35 lines
1.2 KiB
ReStructuredText
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Subscriptions
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=============
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A GraphQL subscription is essentially a query where the client receives an event whenever the value of any field changes
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upstream. The Hasura GraphQL engine supports subscriptions for all kind of queries. All the concepts of
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:doc:`queries <../queries/index>` hold true with subscriptions as well.
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You can turn any query into a subscription by simply replacing ``query`` with ``subscription`` as the operation type.
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.. admonition:: Caveat
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The `GraphQL spec <http://facebook.github.io/graphql/June2018/#sec-Single-root-field>`_ allows for only one root
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field in a subscription. So though Hasura GraphQL engine supports multiple root fields in subscriptions, most clients
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will not allow it.
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Some use cases
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--------------
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- :ref:`subscribe_field`
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- :ref:`subscribe_table`
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- :ref:`subscribe_derived`
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Protocol
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--------
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Hasura GraphQL engine uses the `GraphQL over Websocket Protocol
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<https://github.com/apollographql/subscriptions-transport-ws/blob/master/PROTOCOL.md>`_ by the
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`apollographql/subscriptions-transport-ws <https://github.com/apollographql/subscriptions-transport-ws>`_ library
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for sending and receiving events.
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.. toctree::
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:maxdepth: 1
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:hidden:
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Sample use cases <use-cases>
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