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69 lines
2.5 KiB
ReStructuredText
69 lines
2.5 KiB
ReStructuredText
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How Hasura GraphQL engine works
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===============================
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.. contents:: Table of contents
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:backlinks: none
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:depth: 1
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:local:
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Given a Postgres database, Hasura GraphQL engine can automatically generate a GraphQL schema and process GraphQL
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queries, subscriptions and mutations. Here’s what Hasura GraphQL engine does under the hood.
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Schema generation
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-----------------
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Hasura GraphQL engine automatically generates GraphQL schema components when you track a
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Postgres table/view in Hasura and create relationships between them.
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Tables
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^^^^^^
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When you track a Postgres table in Hasura GraphQL engine, it automatically generates the following for it:
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- A GraphQL type definition for the table
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- A Query field with ``where``, ``order_by``, ``limit`` and ``offset`` arguments
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- A Subscription field with ``where``, ``order_by``, ``limit`` and ``offset`` arguments
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- An Insert mutation field with ``on_conflict`` argument that supports upsert and bulk inserts
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- An Update mutation field with ``where`` argument that supports bulk updates
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- A Delete mutation field with ``where`` argument that supports bulk deletes
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Views
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^^^^^
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When you track a Postgres view in Hasura GraphQL engine, it automatically generates the following for it:
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- A GraphQL type definition for the view
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- A Query field with ``where``, ``order_by``, ``limit`` and ``offset`` arguments
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- A Subscription field with ``where``, ``order_by``, ``limit`` and ``offset`` arguments
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Essentially Hasura GraphQL engine does the same thing it would do for a table, but without creating the insert, update
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and delete mutations.
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Relationships
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^^^^^^^^^^^^^
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When you create a relationship between a table/view with another table/view in Hasura GraphQL engine, it does the
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following:
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- Augments the type of the table/view by adding a reference to the nested type to allow fetching nested objects.
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- Augments the ``where`` and ``order_by`` clauses to allow filtering and sorting based on nested objects.
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Resolvers
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---------
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Hasura GraphQL engine does not have any resolvers. The Hasura GraphQL engine is actually a compiler that compiles
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your GraphQL query into an SQL query.
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Hasura's GraphQL syntax is also optimized to expose the power of the underlying SQL so that you can make powerful
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queries via GraphQL.
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Metadata
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--------
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All the information required for schema generation is stored by Hasura GraphQL engine as metadata in a specific
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Postgres schema in the database. See :doc:`metadata schema <metadata-schema>` for more details.
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.. toctree::
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:maxdepth: 1
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:hidden:
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Metadata schema <metadata-schema>
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