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108 lines
3.3 KiB
ReStructuredText
108 lines
3.3 KiB
ReStructuredText
.. meta::
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:description: Set default field values using SQL functions
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:keywords: hasura, docs, schema, default value, sql function, stored procedure
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.. _sql_functions_as_default:
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Setting values of fields using SQL functions/stored procedures
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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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Let's say you want to set the value of some fields as the output of some custom SQL functions or stored procedures.
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This is useful to set values of fields which depend on other fields passed in the input. E.g. set
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``submission_time`` of an online quiz as 1 hour from the ``start_time``.
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This can be achieved by:
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#. Modifying the table to allow the columns we want to be set by the SQL functions to be nullable (to allow the initial
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insert before the SQL function is run).
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#. Creating an insert/update trigger on the table that calls your SQL function and sets the output values in the output
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columns.
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#. Making your mutation requests without setting the SQL function output columns.
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.. note::
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This approach enforces the value set in the field to always be the result of the defined SQL function even if a
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value is explicitly passed in the insert object.
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**For example**, say we have a table ``sql_function_table`` with columns ``input`` and ``output`` and we would like
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to set the value of the ``output`` column as the uppercased value of the string received in the ``input`` field.
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Step 1: Modify the table
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------------------------
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Modify the table ``sql_function_table`` and make its ``output`` column nullable.
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Open the console and head to ``Data -> sql_function_table -> Modify``:
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.. thumbnail:: /img/graphql/manual/schema/modify-sql-fn-table.png
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:alt: Modify the table
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Step 2: Create a trigger
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------------------------
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The below SQL defines a ``trigger`` which will simply uppercase the value passed in the ``input`` field and set it to
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the ``output`` field whenever an insert or update is made to the ``sql_function_table``:
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.. code-block:: plpgsql
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CREATE FUNCTION test_func() RETURNS trigger AS $emp_stamp$
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BEGIN
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NEW.output := UPPER(NEW.input);
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RETURN NEW;
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END;
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$emp_stamp$ LANGUAGE plpgsql;
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CREATE TRIGGER test_trigger BEFORE INSERT OR UPDATE ON sql_function_table
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FOR EACH ROW EXECUTE PROCEDURE test_func();
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Head to ``Data -> SQL`` and run the above SQL:
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.. thumbnail:: /img/graphql/manual/schema/create-trigger.png
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:alt: Create a trigger with SQL
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Step 3: Run an insert mutation
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------------------------------
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Run a mutation to insert an object with (input = "yabba dabba doo!", output=null) and you'll see the output
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value (output="YABBA DABBA DOO!") will be set automatically.
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.. graphiql::
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:view_only:
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:query:
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mutation {
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insert_sql_function_table (
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objects: [
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{input: "yabba dabba doo!"}
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]
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) {
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returning {
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input
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output
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}
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}
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}
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:response:
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{
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"data": {
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"insert_sql_function_table": {
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"returning": [
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{
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"input": "yabba dabba doo!",
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"output": "YABBA DABBA DOO!"
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}
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]
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}
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}
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}
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Also see
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--------
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- :ref:`postgres_defaults`
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- :ref:`column_presets`
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