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Automate Document Approvals with Multi-Level Workflows using Supabase & Gmail

https://n8nworkflows.xyz/workflows/automate-document-approvals-with-multi-level-workflows-using-supabase---gmail-8174

Automate Document Approvals with Multi-Level Workflows using Supabase & Gmail

1. Workflow Overview

This workflow automates a multi-level document approval process using Supabase as the backend database and Gmail for email notifications. It is designed for organizations that require structured approvals for documents such as policies, contracts, or proposals with audit trail capabilities.

The workflow consists of the following logical blocks:

  • 1.1 Form Submission and Document Storage: Captures a submitted document via a form trigger, uploads it to Supabase storage, and saves document metadata to the documents table.

  • 1.2 Initial Workflow Level and Approver Assignment: Retrieves the first approval level, fetches users assigned to the respective role, generates unique tokens for each approver, creates approval records, and sends email notifications with approval links.

  • 1.3 Approval Link Processing (Webhook Entry Point): Handles incoming approval or rejection decisions from approvers clicking email links. Retrieves the corresponding approval record based on the token and updates its status.

  • 1.4 Decision Evaluation and Workflow Progression: Based on the approval decision, determines whether to reject the document immediately or proceed to the next approval level. If there is a next level, assigns new approvers, generates tokens, sends emails, and logs audit events. If it is the last level, updates the document status to Approved.

  • 1.5 Audit Logging: Records all key workflow events such as approvals sent, approvals granted, and rejections in the audit_logs table for compliance and traceability.

2. Block-by-Block Analysis

2.1 Form Submission and Document Storage

Overview:
This block captures document submission via a form, uploads the binary file to Supabase storage, and saves document metadata to Supabase’s documents table.

Nodes Involved:

  • start_approval_form (Form Trigger)
  • upload_to_supabase_storage (HTTP Request)
  • save_document (Supabase)
  • get_workflow_level_one (Supabase)
  • get_user_by_role (Supabase)
  • create_uuid_token (Crypto)
  • create_record_approvals (Supabase)
  • fetch_file_to_review (HTTP Request)
  • send_email (Gmail)
  • audit_invites (Supabase)
  • end_form (Form Completion)

Node Details:

  • start_approval_form

    • Type: Form Trigger
    • Captures user input: Document Title (string), Description (textarea), and a PDF file upload (required).
    • Path: approval-process-start
    • Outputs form data to start the document approval process.

  • upload_to_supabase_storage

    • Type: HTTP Request
    • Uploads the submitted file binary to Supabase Storage bucket test-n8n.
    • Uses Supabase API credentials for authentication.
    • URL constructed dynamically with filename from form submission.
    • Potential failure: File upload failure, credential errors.

  • save_document

    • Type: Supabase node
    • Inserts a new record into documents table with fields: title, content (filename), submitted_by (hardcoded as 1), and status set to "Pending".
    • Credentials: Supabase API
    • Input from previous node’s binary upload metadata.

  • get_workflow_level_one

    • Type: Supabase
    • Retrieves the first workflow level (where level_number = 1) from workflow_levels table.
    • Used to determine the initial approver role.

  • get_user_by_role

    • Type: Supabase
    • Fetches all users having the role ID retrieved from the workflow level.
    • Returns all approvers for level one.

  • create_uuid_token

    • Type: Crypto (Generate UUID)
    • Generates a unique token for secure approval links.

  • create_record_approvals

    • Type: Supabase
    • Creates individual approval records in approvals table with document ID, level ID, approver ID, generated token, status set to the document status (Pending), and expiry time 48 hours ahead.
    • Credentials: Supabase API.

  • fetch_file_to_review

    • Type: HTTP Request
    • Downloads the uploaded document file from Supabase Storage for email attachment.
    • Uses Supabase credentials.

  • send_email

    • Type: Gmail
    • Sends email to each approver with approval and rejection links including their unique token.
    • Email subject includes document title.
    • Credentials: Gmail OAuth2.
    • Potential failure: Email sending errors, invalid recipient email.

  • audit_invites

    • Type: Supabase
    • Logs audit event in audit_logs indicating approval requests sent for level 1.
    • Fields include document ID, action approval_sent, system actor email, and details with level and role info.

  • end_form

    • Type: Form Completion
    • Marks the form submission process as complete with a confirmation message "Approval Workflow Started."

2.2 Approval Link Processing (Webhook Entry Point)

Overview:
Handles approval or rejection clicks from email links by approvers. Validates token, updates approval record status, and triggers decision logic.

Nodes Involved:

  • Webhook (Webhook)
  • get_approval_data (Supabase)
  • If (If)
  • update_approval_data (Supabase)
  • check_reject_or_approve (If)
  • response_message, response_message1, response_message2 (Set)
  • Respond to Webhook1 (Respond to Webhook)

Node Details:

  • Webhook

    • Type: Webhook
    • Path: approve
    • Entry point triggered by HTTP GET requests when approver clicks email links.
    • Captures query parameters: token and decision (approved/rejected).

  • get_approval_data

    • Type: Supabase
    • Fetches approval record from approvals table matching the token from webhook query.
    • If no record found, triggers empty check.

  • If

    • Type: If
    • Checks if approval data is empty (invalid or expired token).
    • If empty, sends a "Not a value token" response and ends workflow.

  • update_approval_data

    • Type: Supabase
    • Updates the approval record matching approver ID, status Pending, and token.
    • Sets status to webhook decision and records acted_at timestamp.

  • check_reject_or_approve

    • Type: If
    • Evaluates if decision is "approved".
    • If approved, proceeds with workflow level progression; else updates document status to Rejected.

  • response_message

    • Type: Set
    • Sets response text to "Not a value token" for invalid tokens.

  • response_message1

    • Type: Set
    • Sets response text to "Rejected" after rejection.

  • response_message2

    • Type: Set
    • Sets response text to "Approved" after approval.

  • Respond to Webhook1

    • Type: Respond to Webhook
    • Sends the final textual response to the approver’s browser confirming workflow completion or errors.

2.3 Decision Evaluation and Workflow Progression

Overview:
Processes the approval decision, updates document status if rejected, or moves the approval process to the next level if approved.

Nodes Involved:

  • check_reject_or_approve (If)
  • Final Update Document (Supabase)
  • get_level_details (Supabase)
  • get_next_level (Supabase)
  • is_last_level (If)
  • get_workflow_by_level (Supabase)
  • get_user_by_role1 (Supabase)
  • generate_uuid (Crypto)
  • create_approval_record (Supabase)
  • get_document_details (Supabase)
  • fetch_file_to_review1 (HTTP Request)
  • send_emai_by_level (Gmail)
  • Audit1 (Supabase)
  • Audit (Supabase)
  • Final Update Document (Supabase)

Node Details:

  • check_reject_or_approve

    • If node decides approval path or rejection path.
    • Rejection path directly updates document status to "Rejected".
    • Approval path continues workflow.

  • Final Update Document

    • Updates the documents table record status and timestamp based on approval or rejection results.

  • get_level_details

    • Retrieves current approval level data from workflow_levels.

  • get_next_level

    • Fetches next workflow level having level_number greater than current.

  • is_last_level

    • Checks if get_next_level returned any record.
    • If no next level, document is approved final; else proceed to next level.

  • get_workflow_by_level

    • Retrieves workflow level details for next level.

  • get_user_by_role1

    • Fetches users assigned to the next level's role.

  • generate_uuid

    • Generates unique tokens for next level approvers.

  • create_approval_record

    • Inserts new approval records for next level approvers with token and expiry.

  • get_document_details

    • Retrieves document metadata for email content.

  • fetch_file_to_review1

    • Fetches document file from Supabase storage for attachment.

  • send_emai_by_level

    • Sends approval request emails to next level approvers with links.

  • Audit1

    • Logs audit event for approval sent at next level.

  • Audit

    • Logs audit event for final update (approval or rejection).

3. Summary Table

Node Name Node Type Functional Role Input Node(s) Output Node(s) Sticky Note
Webhook Webhook Entry point for approval decision — get_approval_data Triggered when approver clicks approval/rejection link. Captures token and decision.
get_approval_data Supabase Retrieve approval record by token Webhook If
If If Check if approval record exists get_approval_data update_approval_data, response_message
update_approval_data Supabase Update approval status and timestamp If (approval record exists) check_reject_or_approve
check_reject_or_approve If Decision check approve or reject update_approval_data get_level_details, Final Update Document
Final Update Document Supabase Update document status and timestamp check_reject_or_approve, is_last_level Audit
get_level_details Supabase Get current workflow level details check_reject_or_approve get_next_level
get_next_level Supabase Get next workflow level get_level_details is_last_level
is_last_level If Check if current level is last get_next_level get_workflow_by_level, Final Update Document
get_workflow_by_level Supabase Get workflow details by level number is_last_level (true branch) get_user_by_role1
get_user_by_role1 Supabase Get users by role for next level get_workflow_by_level generate_uuid
generate_uuid Crypto Generate unique tokens for approvals get_user_by_role1 create_approval_record
create_approval_record Supabase Create approval records for next level generate_uuid get_document_details
get_document_details Supabase Retrieve document metadata create_approval_record fetch_file_to_review1
fetch_file_to_review1 HTTP Request Fetch document file for email get_document_details send_emai_by_level
send_emai_by_level Gmail Send approval request emails fetch_file_to_review1 Audit1
Audit1 Supabase Log audit entry for approval sent send_emai_by_level response_message2
Audit Supabase Log final audit entry (approved/rejected) Final Update Document response_message1
response_message Set Response for invalid token If (empty approval data) Respond to Webhook1
response_message1 Set Response message after rejection Audit Respond to Webhook1
response_message2 Set Response message after approval Audit1 Respond to Webhook1
Respond to Webhook1 Respond to Webhook Send HTTP response to approver response_message, response_message1, response_message2 —
start_approval_form Form Trigger Capture document submission — upload_to_supabase_storage User submits document via form.
upload_to_supabase_storage HTTP Request Upload file to Supabase storage start_approval_form save_document
save_document Supabase Save document metadata upload_to_supabase_storage get_workflow_level_one
get_workflow_level_one Supabase Get first workflow level save_document get_user_by_role
get_user_by_role Supabase Get users by role for level one get_workflow_level_one create_uuid_token
create_uuid_token Crypto Generate unique token get_user_by_role create_record_approvals
create_record_approvals Supabase Create approval records for level one create_uuid_token fetch_file_to_review
fetch_file_to_review HTTP Request Fetch document for email attachment create_record_approvals send_email
send_email Gmail Send approval email fetch_file_to_review audit_invites
audit_invites Supabase Log approval sent audit entry send_email end_form
end_form Form Marks form completion audit_invites —
Sticky Note Sticky Note Workflow overview and instructions — — See note content in Section 5.
Sticky Note1 Sticky Note Database schema details — — See note content in Section 5.
Sticky Note2 Sticky Note Reminder to update Supabase storage URL — —
Sticky Note3 Sticky Note Label for Form Submit flow — —
Sticky Note4 Sticky Note Label for Next Level Approval — —

4. Reproducing the Workflow from Scratch

  1. Create a Form Trigger node (start_approval_form):

    • Set path to approval-process-start.
    • Add form fields:
      • Title (text, required)
      • Description (textarea)
      • File upload (accept .pdf, required)
    • Enable "Ignore Bots", set button label as "Send for Approval".

  2. Add HTTP Request node (upload_to_supabase_storage):

    • Method: POST
    • URL: https://<your_project_id>.supabase.co/storage/v1/object/test-n8n/{{ $binary.data.fileName }}
    • Authentication: Use Supabase API credentials.
    • Send binary data from form.
    • Input field: data

  3. Add Supabase node (save_document):

    • Operation: Insert
    • Table: documents
    • Fields:
      • title: from form Title field
      • content: file name from upload node
      • submitted_by: hardcoded 1 (can customize)
      • status: "Pending"
    • Use Supabase credentials.

  4. Add Supabase node (get_workflow_level_one):

    • Operation: Get
    • Table: workflow_levels
    • Filter: level_number equals 1
    • Use Supabase credentials.

  5. Add Supabase node (get_user_by_role):

    • Operation: Get All
    • Table: users
    • Filter: role_id equals the role_id from get_workflow_level_one result
    • Use Supabase credentials.

  6. Add Crypto node (create_uuid_token):

    • Action: Generate UUID

  7. Add Supabase node (create_record_approvals):

    • Operation: Insert
    • Table: approvals
    • Fields:
      • document_id: save_document ID
      • level_id: get_workflow_level_one ID
      • approver_id: user ID from get_user_by_role
      • token: UUID from create_uuid_token
      • status: save_document status
      • expiry_time: current time + 48 hours

  8. Add HTTP Request node (fetch_file_to_review):

    • Method: GET
    • URL: file URL from Supabase storage using filename from upload node
    • Authentication: Supabase credentials

  9. Add Gmail node (send_email):

    • To: email from create_uuid_token (assumed user email)
    • Subject: "Document Approval Request - {{document title}}"
    • Message: Include approve and reject links with tokens and decisions as URL parameters.
    • Attach the file binary from fetch_file_to_review.
    • Use Gmail OAuth2 credentials.

  10. Add Supabase node (audit_invites):

    • Operation: Insert
    • Table: audit_logs
    • Fields:
      • document_id: from save_document
      • action: "approval_sent"
      • actor_email: "system@workflow"
      • details: level and role info

  11. Add Form node (end_form):

    • Operation: Completion
    • Completion message: "Approval Workflow Started."

  12. Connect nodes sequentially from form trigger through upload, save document, get workflow level, get users, generate tokens, create approvals, fetch file, send email, audit log, to form completion.

  1. Add Webhook node (Webhook):

    • Path: approve
    • Method: GET
    • Captures query parameters: token, decision

  2. Add Supabase node (get_approval_data):

    • Operation: Get
    • Table: approvals
    • Filter by token from webhook query

  3. Add If node (If):

    • Condition: Check if result from get_approval_data is empty
    • True: Set response message "Not a value token" and respond webhook
    • False: Continue

  4. Add Supabase node (update_approval_data):

    • Operation: Update
    • Table: approvals
    • Filter by approver_id, status=Pending, and token
    • Set status to decision from webhook, set acted_at to now

  5. Add If node (check_reject_or_approve):

    • Condition: Check if decision = "approved"
    • If Yes: Proceed to next level workflow logic
    • If No: Update document status to "Rejected"

  6. Add Supabase node (Final Update Document):

    • Operation: Update
    • Table: documents
    • Filter by document ID from approval data
    • Update status and updated_at timestamp

  7. Add Supabase node (get_level_details):

    • Operation: Get
    • Table: workflow_levels
    • Filter by current approval level ID from approval data

  8. Add Supabase node (get_next_level):

    • Operation: Get All (limit 1)
    • Table: workflow_levels
    • Filter: level_number > current level number

  9. Add If node (is_last_level):

    • Condition: Check if get_next_level output is empty (last level)
    • If True: Update document status to "Approved" (connect to Final Update Document)
    • If False: Continue to next level approvals

  10. Add Supabase node (get_workflow_by_level):

    • Operation: Get
    • Table: workflow_levels
    • Filter by next level number

  11. Add Supabase node (get_user_by_role1):

    • Operation: Get All
    • Table: users
    • Filter by role ID from next level

  12. Add Crypto node (generate_uuid):

    • Generate UUID for next level approvers

  13. Add Supabase node (create_approval_record):

    • Insert new approval records for next level approvers with generated tokens, expiry, and status Pending

  14. Add Supabase node (get_document_details):

    • Get document metadata (title, content) for email

  15. Add HTTP Request node (fetch_file_to_review1):

    • Fetch document file from Supabase Storage for email attachment

  16. Add Gmail node (send_emai_by_level):

    • Send approval request emails to next level approvers with approve/reject links

  17. Add Supabase node (Audit1):

    • Log audit event for approvals sent at next level

  18. Add Supabase node (Audit):

    • Log audit event after final document status update

  19. Add Set nodes (response_message, response_message1, response_message2) to set response texts for various webhook responses.

  20. Add Respond to Webhook node (Respond to Webhook1) to send final HTTP response.

  21. Connect all nodes logically as per the data flow with appropriate error checks.

5. General Notes & Resources

Note Content Context or Link
## Multi-Level Document Approval & Audit Workflow

This workflow automates a document approval process using Supabase and Gmail.

### Who it’s for
- Teams requiring structured multi-level approvals.
- Companies managing policies, contracts, or proposals.
- Users leveraging Supabase backend.

### How to set up
- Configure Supabase credentials.
- Adjust table and field names to your schema.
- Connect Gmail OAuth2.
- Adjust expiry time (default 48h).
- Deploy and test via Form Trigger.

### Customization
- Add multiple approval levels.
- Replace Gmail with other notification channels.
- Update endpoint URLs as per environment.
- Handle errors on DB interactions.

### Email Template includes approve/reject links with tokens.
See sticky note content in workflow.		 Workflow documentation included as Sticky Note node in the workflow. See Section 1 and 2.
## Database Schema example:
Includes tables: roles, users, documents, workflow_levels, approvals, audit_logs.
Defines relationships, keys, and fields needed for workflow.

See detailed SQL schema in Sticky Note1 node.

Ensure your Supabase project tables match these structures or adjust queries accordingly.		 Database schema definitions provided in Sticky Note1 node inside the workflow.
Update URLs in HTTP Request nodes for Supabase Storage upload/download to match your Supabase project ID and bucket name.

Example URL: https://<your_project_id>.supabase.co/storage/v1/object/test-n8n/{{ fileName }}		 Sticky Note2 reminder for correct Supabase storage URL configuration.
The approval URLs in emails use localhost and test environment paths:
http://localhost:5678/webhook-test/doc-approval?token=...&decision=...

Update these URLs for production deployment to your actual n8n instance and remove /webhook-test if appropriate.		 Email template links in Gmail nodes require environment-specific adjustment.
Audit logs capture detailed information about document approvals, rejections, and approval requests sent at each level.

This supports compliance and traceability requirements.		 Audit logging is performed in multiple Supabase nodes named Audit, Audit1, and audit_invites.

This documentation provides a full structured reference for understanding, reproducing, and extending the Multi-Level Document Approval & Audit Workflow implemented in n8n using Supabase and Gmail.

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