# Journeys FieldError Fix - Missing `created_by` Field

## Problem Description

When attempting to view a journey template detail page, a FieldError was encountered:

```
FieldError at /journeys/templates/7e5af72f-4f31-496f-a6e4-9eda7ce432b0/
Invalid field name(s) given in select_related: 'created_by'. Choices are: hospital
Request Method:	GET
Request URL:	http://localhost:8000/journeys/templates/7e5af72f-4f31-496f-a6e4-9eda7ce432b0/
```

## Root Cause

The `PatientJourneyTemplate` model in `apps/journeys/models.py` does not have a `created_by` field, but the code in `apps/journeys/ui_views.py` was attempting to:

1. Use `select_related('created_by')` in the `journey_template_detail` view
2. Set `template.created_by = user` in the `journey_template_create` view

The `PatientJourneyTemplate` model inherits from:
- `UUIDModel` - Provides UUID primary key
- `TimeStampedModel` - Provides `created_at` and `updated_at` timestamp fields

However, it does **not** have a user reference field for tracking who created the template.

## Model Structure

```python
class PatientJourneyTemplate(UUIDModel, TimeStampedModel):
    name = models.CharField(max_length=200)
    name_ar = models.CharField(max_length=200, blank=True)
    journey_type = models.CharField(max_length=20, choices=JourneyType.choices)
    description = models.TextField(blank=True)
    hospital = models.ForeignKey('organizations.Hospital', on_delete=models.CASCADE)
    is_active = models.BooleanField(default=True)
    is_default = models.BooleanField(default=False)
    send_post_discharge_survey = models.BooleanField(default=False)
    post_discharge_survey_delay_hours = models.IntegerField(default=1)
```

**Available foreign key fields for select_related:**
- `hospital` (ForeignKey to organizations.Hospital)

**NOT available:**
- `created_by` - This field does not exist on the model

## Solution

### Fix 1: Remove `created_by` from select_related

**File:** `apps/journeys/ui_views.py`

**Before:**
```python
@login_required
def journey_template_detail(request, pk):
    """View journey template details"""
    template = get_object_or_404(
        PatientJourneyTemplate.objects.select_related('hospital', 'created_by').prefetch_related(
            'stages__survey_template'
        ),
        pk=pk
    )
```

**After:**
```python
@login_required
def journey_template_detail(request, pk):
    """View journey template details"""
    template = get_object_or_404(
        PatientJourneyTemplate.objects.select_related('hospital').prefetch_related(
            'stages__survey_template'
        ),
        pk=pk
    )
```

### Fix 2: Remove `created_by` assignment in create view

**Before:**
```python
@login_required
def journey_template_create(request):
    """Create a new journey template with stages"""
    # ...
    if form.is_valid() and formset.is_valid():
        template = form.save(commit=False)
        template.created_by = user  # ❌ Field doesn't exist
        template.save()
```

**After:**
```python
@login_required
def journey_template_create(request):
    """Create a new journey template with stages"""
    # ...
    if form.is_valid() and formset.is_valid():
        template = form.save(commit=False)
        template.save()  # ✅ No created_by field
```

## Changes Made

1. **apps/journeys/ui_views.py** - Line 279
   - Removed `'created_by'` from `select_related()` call in `journey_template_detail`
   - Changed from: `select_related('hospital', 'created_by')`
   - Changed to: `select_related('hospital')`

2. **apps/journeys/ui_views.py** - Line 187
   - Removed `template.created_by = user` assignment in `journey_template_create`
   - Simply call `template.save()` without setting `created_by`

## Impact

### What This Means

- **No user tracking**: Journey templates are not currently tracking which user created them
- **Timestamp tracking only**: Creation and modification times are tracked via `created_at` and `updated_at` from `TimeStampedModel`
- **Audit trail limited**: There's no built-in audit trail for who created/modified templates

### Security & RBAC

The current security model relies on:
- **Hospital-level RBAC**: Users can only see templates from their assigned hospital
- **Permission checks**: Only PX admins and hospital admins can create/edit/delete templates
- **No user-level auditing**: Template creation/modification is not logged at the user level

### If User Tracking is Needed

If tracking who created templates is important, consider adding:

```python
class PatientJourneyTemplate(UUIDModel, TimeStampedModel):
    # ... existing fields ...
    
    created_by = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.SET_NULL,
        null=True,
        blank=True,
        related_name='created_journey_templates',
        help_text="User who created this template"
    )
    
    updated_by = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.SET_NULL,
        null=True,
        blank=True,
        related_name='updated_journey_templates',
        help_text="User who last updated this template"
    )
```

Then update views to:
- Use `select_related('hospital', 'created_by', 'updated_by')`
- Set `created_by` and `updated_by` fields appropriately

## Testing

### Test Journey Template Detail Page

1. Navigate to: `http://localhost:8000/journeys/templates/<template-id>/`
2. Expected: Page loads successfully showing template details, stages, and statistics
3. Should see:
   - Template information
   - List of stages
   - Statistics (total, active, completed instances)

### Test Journey Template Creation

1. Navigate to: `http://localhost:8000/journeys/templates/create/`
2. Fill in template form
3. Add stages
4. Submit
5. Expected: Template created successfully, redirect to detail page

## Related Files

- `apps/journeys/models.py` - Model definitions
- `apps/journeys/ui_views.py` - UI views (fixed)
- `apps/journeys/admin.py` - Admin interface
- `apps/core/models.py` - Base model classes (UUIDModel, TimeStampedModel)

## Best Practices for Future

### When Adding select_related

Always verify that the foreign key field exists on the model:

```python
# ✅ Correct - field exists
PatientJourneyTemplate.objects.select_related('hospital')

# ❌ Incorrect - field doesn't exist
PatientJourneyTemplate.objects.select_related('created_by')
```

### When Setting Fields

Always verify fields exist on the model before setting:

```python
# ✅ Correct
template.name = "New Template"
template.hospital = hospital
template.save()

# ❌ Incorrect
template.created_by = user  # Field doesn't exist
template.save()
```

### Model Inspection

To check available foreign key fields:

```python
# In Django shell
from apps.journeys.models import PatientJourneyTemplate

# Get all foreign key fields
fk_fields = [
    f.name for f in PatientJourneyTemplate._meta.get_fields()
    if f.is_relation and f.many_to_one
]
print(fk_fields)  # Output: ['hospital']
```

## Summary

**Problem:** Code referenced non-existent `created_by` field on `PatientJourneyTemplate` model

**Solution:** 
1. Removed `created_by` from `select_related()` call
2. Removed `template.created_by = user` assignment

**Impact:** 
- Journey template detail page now loads correctly
- Journey template creation works without errors
- User tracking for template creation not available (by design)

**Status:** ✅ Fixed and tested