Setting default values for fields
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Let's say you want certain fields to have their values set automatically when not explicitly passed. You can do this in
the following ways:

- :doc:`Postgres defaults <postgres-defaults>`: configure default values, using fixed values or simple SQL functions,
  for columns in the table definition. e.g. an auto-incrementing ``id``, a ``created_at`` timestamp, etc.
- :doc:`Custom SQL functions <sql-functions>`: set up Postgres triggers which run custom SQL functions/stored procedures
  to set the values of certain columns on inserts/updates on the table. This is useful to set values of fields which
  depend on other fields passed in the input. e.g. set ``submission_time`` of an online quiz as 1 hour from the
  ``start_time``.
- :doc:`Role based column presets <column-presets>`: set up presets, using session variables or fixed values, that are
  applied when a new row is created with a particular :doc:`user role <../../auth/roles-variables>`. e.g. set a
  ``user_id`` field automatically from a session variable/Authorization header.

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  Postgres defaults <postgres-defaults>
  Custom SQL functions/stored procedures <sql-functions>
  Role based column presets <column-presets>