makeSetDefaultOrderByForFieldPlugin.ts

import { Plugin } from 'postgraphile';

/**
 * Allows you to override the default orderBy for a given field to be the
 * orderBy with the given name. Usage:
 *
 * ```
 * const MyOrderByPlugin = makeSetDefaultOrderByForFieldPlugin(
 *   'MyTableName',
 *   'myRelationName',
 *   'PRIMARY_KEY_DESC'
 * );
 * // ...
 * app.use(postgraphile(DATABASE_URL, SCHEMA_NAMES, {
 *   appendPlugins: [MyOrderByPlugin]
 * }));
 * ```
 */
export default function makeSetDefaultOrderByForFieldPlugin(
  targetTypeName: string,
  targetFieldName: string,
  targetOrderByName: string,
): Plugin {
  // This plugin is heavily based on
  // https://github.com/graphile/graphile-engine/blob/3f22f7698f84be288bf5791bcd9aa30b009ebfd7/packages/graphile-build-pg/src/plugins/PgConnectionArgOrderByDefaultValue.js
  const plugin: Plugin = builder => {
    builder.hook(
      'GraphQLObjectType:fields:field:args',
      (args, build, context) => {
        const { extend, getTypeByName, pgGetGqlTypeByTypeIdAndModifier, inflection } = build;
        const {
          scope: {
            fieldName,
            isPgFieldConnection,
            isPgFieldSimpleCollection,
            pgFieldIntrospection: table,
          },
          Self,
        } = context;

        if (
          !(isPgFieldConnection || isPgFieldSimpleCollection) ||
          !table ||
          table.kind !== 'class' ||
          !table.namespace ||
          !table.isSelectable ||
          !args.orderBy ||
          Self.name !== targetTypeName ||
          fieldName !== targetFieldName
        ) {
          return args;
        }

        const TableType = pgGetGqlTypeByTypeIdAndModifier(table.type.id, null);
        const tableTypeName = TableType.name;
        const TableOrderByType = getTypeByName(inflection.orderByType(tableTypeName));
        if (!TableOrderByType) {
          throw new Error(`Could not find orderBy type for field '${Self.name}.${fieldName}'`);
        }

        const targetValueEnum = TableOrderByType.getValues().find(
          v => v.name === targetOrderByName,
        );
        if (!targetValueEnum) {
          throw new Error(
            `Could not find orderBy enum value named '${targetOrderByName}' for field '${targetTypeName}.${targetFieldName}'`,
          );
        }

        return extend(args, {
          orderBy: extend(
            args.orderBy,
            {
              defaultValue: targetValueEnum,
            },
            `Setting defaultValue on orderBy arg for field '${Self.name}.${fieldName}'`,
          ),
        });
      },
      // This hook provides:
      [],
      // Make sure this hook runs before:
      ['PgConnectionArgOrderByDefaultValue'],
    );
  };

  // A pretty name for debugging
  plugin.displayName = `Set_${targetTypeName}_${targetFieldName}_orderByDefaultTo_${targetOrderByName}_Plugin`;

  return plugin;
}