Here is a custom action i need to check if a Address already exists in the database.
I cant use a backend query since this cannot be set in a action. Also I cant use this default flutterflow fetching process since I make my ID fields in a custom format like Youtube. But FF does not alow a ID field to be empty when its a primary key.

// Automatic FlutterFlow imports\nimport '/backend/schema/structs/index.dart';\nimport '/backend/supabase/supabase.dart';\nimport '/flutter_flow/flutter_flow_theme.dart';\nimport '/flutter_flow/flutter_flow_util.dart';\nimport '/custom_code/actions/index.dart'; // Imports other custom actions\nimport '/flutter_flow/custom_functions.dart'; // Imports custom functions\nimport 'package:flutter/material.dart';\n// Begin custom action code\n// DO NOT REMOVE OR MODIFY THE CODE ABOVE!\n\nFuture<String?> getAddress(\n  String houseAddress,\n  String houseNumber,\n  String postalCode,\n  String city,\n  String township,\n  String province,\n  String country,\n) async {\n  final supabase = SupaFlow.client;\n\n  final response = await supabase\n      .from('address')\n      .select('id')\n      .eq('street_address', houseAddress)\n      .eq('house_number', houseNumber)\n      .eq('postal_code', postalCode)\n      .eq('city', city)\n      .eq('township', township)\n      .eq('province', province)\n      .eq('country', country)\n      .execute();\n\n  // check if the query was succesful and if there was a row returned.\n  if (response.data == null || response.data!.isEmpty) {\n    return null;\n  }\n\n  // Address already exists, return its ID\n  return response.data![0]['id'].toString();\n}

RETURN Type is String (nullable).

But you could also map custom data type to all the fields you want to retrieve and return the datatype.
Hope this helps you.

Using Supabase auth in custom functions/actions?