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65 lines
2.1 KiB
ReStructuredText
65 lines
2.1 KiB
ReStructuredText
.. meta::
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:description: Set default field values using Postgres defaults
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:keywords: hasura, docs, schema, default value, Postgres default
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Setting default values for fields using Postgres defaults
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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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You can set values of certain fields automatically when not explicitly passed to a fixed value, e.g. true for a boolean
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field, or output of a simple SQL function, e.g. now() for a timestamp field, by setting column default values in the
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table definition.
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.. note::
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The Postgres default value is ignored when a value is explicitly set to the field.
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**Example:** Say we have a field ``created_at`` in a table ``article`` which we want to be set to the current
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timestamp whenever a new row is added to the table:
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Step 1: Modify the table
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------------------------
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Edit the ``created_at`` field and set its default value as the SQL function ``now()``.
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Open the console and head to ``Data -> article -> Modify``:
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.. thumbnail:: ../../../../img/graphql/manual/schema/add-default-value.png
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:alt: Modify the table in the console
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.. admonition:: To set an auto-incrementing default value
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To set a default value as an auto-incrementing integer you first need to set up a ``sequence`` which will be the
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source of our default value.
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Let's say we have a field called ``roll_number`` which we would like to be set by default as an auto-incremented
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integer.
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Head to ``Data -> SQL`` and run the following SQL command to create a new sequence.
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.. code-block:: SQL
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CREATE SEQUENCE roll_number_seq;
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Now set the default value of the ``roll_number`` field as ``nextval('roll_number_seq')``.
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Step 2: Run an insert mutation
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------------------------------
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Now if you do not pass the ``created_at`` field value while running an insert mutation on the ``article`` table, its
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value will be set automatically by Postgres.
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.. thumbnail:: ../../../../img/graphql/manual/schema/default-value-response.png
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:alt: Run an insert mutation
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Also see
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--------
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- :doc:`sql-functions`
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- :doc:`column-presets`
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