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Version: v2.x

Postgres: Setting Values of Fields Using SQL Functions


Let's say you want to set the value of some fields as the output of some custom SQL functions (a.k.a. stored procedures). 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.

This can be achieved by:

  1. Modifying the table to allow the columns we want to be set by the SQL functions to be nullable (to allow the initial insert before the SQL function is run).
  2. Creating an insert/update trigger on the table that calls your SQL function and sets the output values in the output columns.
  3. Making your mutation requests without setting the SQL function output columns.

This approach enforces the value set in the field to always be the result of the defined SQL function even if a value is explicitly passed in the insert object.

For example, say we have a table sql_function_table with columns input and output and we would like to set the value of the output column as the uppercased value of the string received in the input field.

Step 1: Modify the table

Modify the table sql_function_table and make its output column nullable.

Open the Console and head to Data -> [sql_function_table] -> Modify:

Modify the table

Step 2: Create a trigger

The below SQL defines a trigger which will simply uppercase the value passed in the input field and set it to the output field whenever an insert or update is made to the sql_function_table:

CREATE FUNCTION test_func() RETURNS trigger AS $emp_stamp$
NEW.output := UPPER(NEW.input);
$emp_stamp$ LANGUAGE plpgsql;

CREATE TRIGGER test_trigger BEFORE INSERT OR UPDATE ON sql_function_table

Head to Data -> SQL and run the above SQL:

Create a trigger with SQL

Step 3: Run an insert mutation

Run a mutation to insert an object with (input = "yabba dabba doo!", output=null) and you'll see the output value (output="YABBA DABBA DOO!") will be set automatically.

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