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75 lines
2.3 KiB
ReStructuredText
75 lines
2.3 KiB
ReStructuredText
.. meta::
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:description: Customise the Hasura GraphQL schema with views
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:keywords: hasura, docs, schema, view
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.. _custom_views:
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Customise schema with views
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===========================
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.. contents:: Table of contents
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:backlinks: none
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:depth: 2
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:local:
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What are views?
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---------------
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`Views <https://www.postgresql.org/docs/current/sql-createview.html>`_ can be used to expose the results of a custom
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query as a virtual table. Views are not persisted physically i.e. the query defining a view is executed whenever
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data is requested from the view.
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Hasura GraphQL engine lets you expose views over the GraphQL API to allow querying them using both ``queries`` and
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``subscriptions`` just like regular tables.
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.. _create_views:
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Creating & exposing views
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-------------------------
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Views can be created using SQL which can be run in the Hasura console:
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- Head to the ``Data -> SQL`` section of the Hasura console
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- Enter your `create view SQL statement <https://www.postgresql.org/docs/current/static/sql-createview.html>`__
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- Select the ``Track this`` checkbox to expose the new view over the GraphQL API
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- Hit the ``Run`` button
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Use cases
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---------
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Views are ideal solutions for retrieving some derived data based on some custom business logic. If your custom logic
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requires any user input, you should use :ref:`custom SQL functions <custom_sql_functions>` instead.
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Let's see a few example use cases for views:
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Example: Group by and then aggregate
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************************************
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Let’s see how to fetch the average article rating for each author in our author/article schema.
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A view that averages the rating of articles for each author can be created using the following SQL query:
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.. code-block:: SQL
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CREATE VIEW author_average_rating AS
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SELECT author_id, avg(rating)
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FROM article
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GROUP BY author_id
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Example: Hide certain fields of a table
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***************************************
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Say, we have some sensitive information in a table which we wouldn't want to expose. We can create a view that only
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exposes the non-sensitive fields.
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Let's say our ``author`` table has the fields ``id, name, city, email, phone, address`` and we want to hide the ``email``,
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``phone`` and ``address`` fields. We can create the following view to achieve this:
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.. code-block:: SQL
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CREATE VIEW author_public AS
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SELECT id, name, city
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FROM author
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