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FIX-CUSTOMER-EMAIL-DUPLICATE.md

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+# Fix Customer Email Duplicate Error
+
+## Problem
+The unique index on `Customers.Email` was enforcing **global uniqueness** (across all companies), but in a multi-tenant system, different companies should be able to have customers with the same email address.
+
+## Solution
+Change the unique index to be scoped to `CompanyId`, allowing the same email across different companies while still preventing duplicates within the same company.
+
+---
+
+## Quick Fix (Run SQL Script)
+
+### Step 1: Run the SQL Script
+1. Open **SQL Server Management Studio**
+2. Connect to your testing server
+3. Open the file: **`fix-customer-email-index.sql`**
+4. **Execute** the script
+
+This will:
+- ✅ Drop the old global unique index
+- ✅ Create new company-scoped unique index
+- ✅ Show verification that it worked
+
+### Step 2: Test Seeding
+1. Go to your web app: `/SeedData`
+2. Click **"Seed Company Data"**
+3. Should work perfectly now! ✨
+
+---
+
+## Alternative: Use EF Migration (For Production Deployment)
+
+If you want to use EF migrations for a cleaner deployment:
+
+### From Web Project Directory:
+```bash
+cd src/PowderCoating.Web
+
+# Apply the migration
+dotnet ef database update --project ../PowderCoating.Infrastructure
+```
+
+This will apply the migration: **`FixCustomerEmailIndexForMultiTenancy`**
+
+---
+
+## What Changed
+
+### Before (Old Index):
+```sql
+CREATE UNIQUE INDEX IX_Customers_Email ON Customers (Email)
+WHERE [Email] IS NOT NULL
+```
+❌ Problem: Only ONE customer across ALL companies can have `john.smith@acmemfg.com`
+
+### After (New Index):
+```sql
+CREATE UNIQUE INDEX IX_Customers_Email ON Customers (CompanyId, Email)
+WHERE [Email] IS NOT NULL AND [IsDeleted] = 0
+```
+✅ Solution: EACH company can have a customer with `john.smith@acmemfg.com`
+
+---
+
+## Examples
+
+### Now This Works:
+| CompanyId | Email | Status |
+|-----------|-------|--------|
+| 1 | john.smith@acmemfg.com | ✅ OK |
+| 2 | john.smith@acmemfg.com | ✅ OK (different company) |
+| 1 | jane.doe@example.com | ✅ OK |
+
+### This Still Prevents Duplicates:
+| CompanyId | Email | Status |
+|-----------|-------|--------|
+| 1 | john.smith@acmemfg.com | ✅ First insert OK |
+| 1 | john.smith@acmemfg.com | ❌ DUPLICATE (same company) |
+
+---
+
+## Verification
+
+After running the script, verify the index:
+
+```sql
+-- Check the new index definition
+SELECT
+    i.name AS IndexName,
+    i.is_unique AS IsUnique,
+    STRING_AGG(COL_NAME(ic.object_id, ic.column_id), ', ') AS IndexColumns,
+    i.filter_definition AS Filter
+FROM sys.indexes i
+INNER JOIN sys.index_columns ic ON i.object_id = ic.object_id AND i.index_id = ic.index_id
+WHERE i.object_id = OBJECT_ID('Customers')
+    AND i.name = 'IX_Customers_Email'
+GROUP BY i.name, i.is_unique, i.filter_definition
+```
+
+**Expected Result:**
+- IndexName: `IX_Customers_Email`
+- IsUnique: `1` (true)
+- IndexColumns: `CompanyId, Email`
+- Filter: `[Email] IS NOT NULL AND [IsDeleted] = 0`
+
+---
+
+## Build & Deploy
+
+The migration is already in your code:
+```
+src/PowderCoating.Infrastructure/Migrations/
+  └─ 20260211160000_FixCustomerEmailIndexForMultiTenancy.cs
+```
+
+When you deploy to production:
+```bash
+dotnet ef database update --project ../PowderCoating.Infrastructure
+```
+
+Will automatically apply this migration.
+
+---
+
+## Summary
+
+✅ **Index Fixed** - Scoped to CompanyId
+✅ **Multi-Tenancy Safe** - Same email OK across companies
+✅ **Duplicate Prevention** - Still blocks duplicates within a company
+✅ **Soft Delete Aware** - Ignores deleted records
+
+You're ready to seed! 🎉