# Migration to oracledb (from cx_Oracle)

## Overview

The project has been updated to use **oracledb** instead of **cx_Oracle**:

### Benefits of oracledb

| Feature | cx_Oracle | oracledb |
|---------|-----------|----------|
| **Oracle Instant Client Required** | ✓ Always | ✗ Not in Thin mode |
| **Setup Complexity** | Complex | Simple |
| **Thin Mode** | ✗ No | ✓ Yes (default) |
| **Modern** | Older | Latest |
| **Python 3.8+** | ✓ | ✓ |
| **Connection Pooling** | ✓ | ✓ |

### What Changed

#### Dependencies

**Before:**
```txt
cx_Oracle==8.3.0
```

**After:**
```txt
oracledb==2.0.0
```

#### Code Changes

**oracle_connector.py:**
- Changed `import cx_Oracle` → `import oracledb`
- Changed `cx_Oracle.SessionPool` → `oracledb.create_pool()`
- Added Thin mode initialization (no Instant Client needed)
- Updated exception handling to `oracledb.DatabaseError`

#### Installation

**Before (cx_Oracle):**
- 1. Install Python package
- 2. Download Oracle Instant Client
- 3. Install Oracle Instant Client
- 4. Set LD_LIBRARY_PATH
- 5. Test connection

**After (oracledb Thin mode):**
- 1. Install Python package → Done! ✓

No Oracle Instant Client needed for Thin mode!

---

## Quick Setup

### Option 1: Thin Mode (Recommended - No Installation)

```bash
# Install dependencies
pip install -r requirements.txt

# That's it! oracledb Thin mode works without Oracle Instant Client
python -c "import oracledb; print('Ready to use!')"
```

**Works for:**
- ✓ Network connections to remote Oracle Database
- ✓ All standard SQL operations
- ✓ Connection pooling
- ✓ Most applications

### Option 2: Thick Mode (If You Have Oracle Instant Client)

If you already have Oracle Instant Client installed, you can optionally use Thick mode:

```bash
# Edit db/oracle_connector.py and uncomment:
# oracledb.init_oracle_client()  # Use Thick mode
```

---

## Testing the Connection

### Test Database Connectivity

```bash
python -c "
import oracledb

# Using Thin mode (default)
try:
    connection = oracledb.connect(
        user='pacs_db',
        password='pacs_db',
        dsn='testipksdb.c7q7defafeea.ap-south-1.rds.amazonaws.com:1521/IPKSDB'
    )
    print('✓ Connected successfully!')
    connection.close()
except Exception as e:
    print(f'Connection error: {e}')
"
```

---

## Configuration

### .env File (No Changes Needed)

The configuration remains the same:

```
DB_USER=pacs_db
DB_PASSWORD=pacs_db
DB_HOST=testipksdb.c7q7defafeea.ap-south-1.rds.amazonaws.com
DB_PORT=1521
DB_SERVICE_NAME=IPKSDB
```

---

## Feature Comparison

### Connection Pooling

Both cx_Oracle and oracledb support connection pooling:

**cx_Oracle:**
```python
pool = cx_Oracle.SessionPool(user='...', password='...', dsn='...')
conn = pool.acquire()
```

**oracledb:**
```python
pool = oracledb.create_pool(user='...', password='...', dsn='...')
conn = pool.acquire()
```

### Query Execution

No changes needed - the API is compatible:

```python
cursor = conn.cursor()
cursor.execute("SELECT * FROM table")
rows = cursor.fetchall()
```

---

## Troubleshooting

### ImportError: No module named 'oracledb'

Install the package:
```bash
pip install oracledb==2.0.0
```

Or install all requirements:
```bash
pip install -r requirements.txt
```

### Connection Failed

1. Verify credentials in .env:
```bash
cat .env | grep DB_
```

2. Test connection directly:
```bash
python -c "
import oracledb
conn = oracledb.connect(
    user='pacs_db',
    password='pacs_db',
    dsn='testipksdb.c7q7defafeea.ap-south-1.rds.amazonaws.com:1521/IPKSDB'
)
print('Connected!')
"
```

3. Check network connectivity:
```bash
# Test if database is reachable
python -c "
import socket
try:
    socket.create_connection(('testipksdb.c7q7defafeea.ap-south-1.rds.amazonaws.com', 1521), timeout=5)
    print('✓ Database server is reachable')
except Exception as e:
    print(f'✗ Cannot reach database: {e}')
"
```

---

## Migration Checklist

- [x] Update requirements.txt (cx_Oracle → oracledb)
- [x] Update oracle_connector.py (imports and API)
- [x] Update exception handling (cx_Oracle → oracledb)
- [x] Test database connection
- [x] Verify all tests pass
- [x] Update documentation

---

## Rollback (If Needed)

If you need to revert to cx_Oracle:

1. Update requirements.txt:
```txt
cx_Oracle==8.3.0
```

2. Update oracle_connector.py:
```python
import cx_Oracle
pool = cx_Oracle.SessionPool(...)
```

3. Install and test:
```bash
pip install -r requirements.txt
python main.py
```

---

## Performance Impact

**No performance difference** - oracledb Thin mode:
- ✓ Same connection pooling
- ✓ Same query execution speed
- ✓ Same transaction handling

The only difference is simplified setup!

---

## Documentation Updates

The following documentation has been updated:

- ✅ SETUP.md - Simplified Oracle client section
- ✅ requirements.txt - Updated to oracledb
- ✅ db/oracle_connector.py - Updated to use oracledb
- ✅ This file - Migration guide

---

## References

- **oracledb Documentation**: https://python-oracledb.readthedocs.io/
- **Thin vs Thick Mode**: https://python-oracledb.readthedocs.io/en/latest/user_guide/initialization.html
- **Connection Pooling**: https://python-oracledb.readthedocs.io/en/latest/user_guide/connection_handling.html

---

## Summary

✅ **Migration to oracledb completed successfully**

**Benefits:**
- No Oracle Instant Client needed (Thin mode)
- Simpler installation (just `pip install`)
- Modern Python Oracle driver
- Same API compatibility
- Better documentation and support

**Migration Status:** Ready for production

**Testing:** All tests passing with oracledb