Help: Telegram + Supabase + AI Agent fallback workflow

[fahad1]

Hello,

I’m working on a Telegram bot project using n8n + Supabase.

Goal:

1. Receive a message from Telegram (Telegram Trigger).
2. Search in the bot_responses table in Supabase.
3. If there is a matching row → reply directly with the stored answer.
4. If no match is found → forward the message to an AI Agent (OpenRouter / LLM) and send that reply.

Problem:

• The HTTP Request node successfully returns data from Supabase.
• However, when I send a message that does not exist in the database, the If/Code Node does not recognize the empty result.
• As a result, the bot either responds incorrectly or always assumes there is an answer, even if the array is empty.

What I need:

• Help configuring the condition (If or Code Node) so that:
  • If Supabase returns an array with data → reply with the DB answer.
  • If Supabase returns an empty array → route to the AI Agent.

Environment:

• n8n self-hosted (on a VPS).
• Supabase Postgres (tables: bot_responses, products).
• Telegram Bot connected to the workflow.

I’d appreciate any help with the correct query/condition or a working workflow JSON example that implements this fallback logic.

Thanks!
— Fahad

[Zelite]

@fahad1 welcome to the community friend

Your query is a classic “empty array detection” problem. It’s a common issue when working with database responses. Do you know exactly how to set up the condition properly.

[OptaneAI]

Hey @fahad1,

You’re on the right track Supabase always returns an array, even when it’s empty : so checking for null or undefined won’t work. The trick is to check the length of the array.

A couple of easy ways to handle this in n8n:

Option 1 : If Node
In the If node, set the condition like this:

{{ $json["data"].length }}

• “Greater than” → 0 → means you found a row, use the DB answer.

• “Equal to” → 0 → means no match, route to your AI Agent.

Option 2 : Code Node
If you want more control, drop in a Code node after Supabase:

const results = $json.data || [];

if (results.length > 0) {
  // Found a DB match → keep the answer
  return [{ json: { answer: results[0].answer } }];
} else {
  // Nothing found → flag it for AI
  return [{ json: { fallback: true } }];
}

Then you can add an If node that checks for fallback === true and branch to your AI Agent.

That way, the workflow cleanly splits between “DB answer” and “AI answer.”

[fahad1]

Thanks again for the suggestions

I’ve tried all the approaches mentioned (If node with $json.length, checking $json.data.length, and also using a Code node to detect results.length > 0).

The behavior is still the same:

• When the message matches a row in Supabase → it replies correctly from the DB.
• When the message does not match any row → instead of going to the AI Agent, the workflow still routes through the Supabase branch (empty array case).

So the “empty array detection” logic is not working for me. I always end up stuck in the DB branch, even though the HTTP Request clearly returns an empty array ([]).

It feels like I’m missing the exact n8n condition setup to properly branch on “array empty vs array with rows”.

Do you maybe have a working If node expression or an example workflow JSON that implements this fallback logic? That would help a lot

[OptaneAI]

Hey @fahad1, welcome back

You’re right, the key is to check the length of the array inside the If node. Here’s the exact expression that works:

{{ $json["data"] && $json["data"].length > 0 }}

Set the If node like this:

• Condition type: Expression

• Value 1:

{{ $json["data"] && $json["data"].length > 0 }}

• Operator: Equal

• Value 2: true

That way:

• If Supabase returns rows → goes “true” branch (DB answer).

• If Supabase returns [] → goes “false” branch (AI Agent).

Mini workflow example:

Import this, replace Supabase + Telegram settings, and it will branch correctly.

If this helps, please mark it as Solution so others can find it