Backend Import Errors

Critical: GraphQL 500 Errors with CORS Failures

Symptoms

  • GraphQL returns 500 errors
  • CORS failures in browser console
  • “Load failed” errors in frontend
  • Backend completely unresponsive

Root Cause

Incorrect imports in the backend Python code cause the entire backend to fail during initialization.

Common Import Errors

# ❌ WRONG - These functions don't exist and crash the backend
from .db_postgres import create_async_engine  # Function doesn't exist
from .db_neo4j import AsyncGraphDatabase       # Function doesn't exist

# ✅ CORRECT - Use actual packages
from sqlalchemy.ext.asyncio import create_async_engine
from neo4j import AsyncGraphDatabase

How to Fix

  1. Check Recent Backend Changes
    • Look for any new or modified Python files
    • Search for import statements from .db_postgres or .db_neo4j
  2. Correct the Imports 
    # PostgreSQL imports
from sqlalchemy.ext.asyncio import create_async_engine
from sqlalchemy import text
   
# Neo4j imports
from neo4j import AsyncGraphDatabase, GraphDatabase
  3. Verify Backend Starts 
    cd Plings-Backend
python -m uvicorn app.main:app --reload
  4. Test GraphQL Endpoint
    • Navigate to http://localhost:8000/graphql
    • Should see GraphiQL interface
    • Try simple query: { _health }

Prevention

  • Always use package imports, not local module imports for database drivers
  • Test backend startup after any import changes
  • Keep imports at top of file and organized by type

This is the #1 cause of “Load failed” errors in the frontend. The backend crashes during initialization, so no endpoints are available, causing CORS errors as a secondary symptom.

See also: