pgSingleTablePolymorphic

This step class gives just one of many ways of supporting polymorphism in @dataplan/pg; we recommend that you read the polymorphism documentation before deciding whether or not you need this step - most likely it is better to use the mode: "single" polymorphism setting on the underlying codec instead.

pgSingleTablePolymorphic is a very simple way of representing a polymorphic type where all of the underlying values are stored in the same table. For example you might have an animals table that stores details of all of your cats, dogs and fish; such as:

create table animals (
  id serial primary key,
  type text not null,
  name text not null,
  date_of_birth date not null,
  number_of_lives boolean,
  wags_tail boolean,
  freshwater boolean
);

In GraphQL we might represent this as an Animal interface, with implementations Cat, Dog and Fish.

You call pgSingleTablePolymorphic($typeName, $row) passing a step indicating the GraphQL type name, and a step representing the row from the table; for example:

const $animal = animalsResource.get({ id: constant(1) });

// 'Cat', 'Dog' or 'Fish'; use a lambda step to transform the values if
// necessary.
const $typeName = $animal.get("type");

return pgSingleTablePolymorphic($typeName, $animal);