fix error and update readme

README.md

@@ -145,7 +145,7 @@ Association table tracking which brands are available in which shops:
 - `created_at`: DateTime, Creation timestamp (auto-generated)
 - `updated_at`: DateTime, Last update timestamp (auto-updated)
 
-### Association Table
+### Association Tables
 
 #### Shopping Event Products (`shopping_event_products` table)
 Many-to-many relationship between shopping events and products with additional data:
@@ -155,6 +155,15 @@ Many-to-many relationship between shopping events and products with additional d
 - `amount`: Float, Quantity purchased in this event (required, > 0)
 - `price`: Float, Price at time of purchase (required, ≥ 0)
 
+#### Related Products (`related_products` table)
+Many-to-many self-referential relationship between products for tracking related items:
+- `id`: Integer, Primary key, Auto-increment
+- `product_id`: Integer, Foreign key to products (required)
+- `related_product_id`: Integer, Foreign key to products (required)
+- `relationship_type`: String, Type of relationship (optional)
+  - Examples: "size_variant", "brand_variant", "similar", "alternative"
+- `created_at`: DateTime, Creation timestamp (auto-generated)
+
 ### Relationships
 
 ```
@@ -172,6 +181,19 @@ Many-to-many relationship between shopping events and products with additional d
         │                     │ • updated_at    │
         │                     └─────────────────┘
         │                              │
+        │                              │ N:M (self-referential)
+        │                              ▼
+        │                     ┌─────────────────────────────┐
+        │                     │    Related Products         │
+        │                     │   (Association Table)       │
+        │                     │                             │
+        │                     │ • id                        │
+        │                     │ • product_id                │
+        │                     │ • related_product_id        │
+        │                     │ • relationship_type         │
+        │                     │ • created_at                │
+        │                     └─────────────────────────────┘
+        │                              │
         │                              │ N:M
         │                              ▼
         │                     ┌─────────────────────────────┐
@@ -217,6 +239,7 @@ Many-to-many relationship between shopping events and products with additional d
 
 - **Direct Product-Category Relationship**: Products are directly linked to categories for simplified organization
 - **Brand Tracking**: Optional brand association for products with shop availability tracking
+- **Related Products**: Track relationships between products (size variants, brand alternatives, similar items)
 - **Price History**: Each product purchase stores the price at that time, enabling price tracking
 - **Flexible Quantities**: Support for decimal amounts (e.g., 1.5 kg of apples)
 - **Auto-calculation**: Total amount can be automatically calculated from individual items
@@ -334,6 +357,14 @@ Many-to-many relationship between shopping events and products with additional d
 - `GET /brands-in-shops/brand/{brand_id}` - Get shops that carry specific brand
 - `DELETE /brands-in-shops/{id}` - Delete brand-shop association
 
+### Related Products
+- `GET /related-products/` - List all product relationships
+- `POST /related-products/` - Create new product relationship
+- `GET /related-products/{id}` - Get specific product relationship
+- `GET /related-products/product/{product_id}` - Get all products related to a specific product
+- `PUT /related-products/{id}` - Update relationship type
+- `DELETE /related-products/{id}` - Delete product relationship
+
 ### Shopping Events
 - `GET /shopping-events/` - List all shopping events
 - `POST /shopping-events/` - Create new shopping event
@@ -352,10 +383,11 @@ Many-to-many relationship between shopping events and products with additional d
 3. **Add Brands**: Create brands for your products (optional)
 4. **Configure Shop-Brand Availability**: Associate brands with shops where they're available
 5. **Add Products**: Create product items linked directly to categories and optionally to brands
-6. **Record Purchases**: Use the "Add Shopping Event" form to record purchases with multiple products
-7. **Track Prices**: Monitor how prices change over time for the same products
-8. **Import/Export Data**: Use CSV files to bulk import or export your data
-9. **View Statistics**: Analyze spending patterns by category and shop
+6. **Link Related Products**: Connect products that are related (e.g., same item in different sizes, brand alternatives)
+7. **Record Purchases**: Use the "Add Shopping Event" form to record purchases with multiple products
+8. **Track Prices**: Monitor how prices change over time for the same products
+9. **Import/Export Data**: Use CSV files to bulk import or export your data
+10. **View Statistics**: Analyze spending patterns by category and shop
 
 ## Deployment
 

backend/schemas.py

@@ -173,7 +173,6 @@ class ShopStats(BaseModel):
 
 # Update forward references
 BrandInShop.model_rebuild()
-ProductWithRelated.model_rebuild()
 
 # Related Products schemas
 class RelatedProductBase(BaseModel):
@@ -199,4 +198,7 @@ class ProductWithRelated(Product):
     related_products: List["Product"] = []
     
     class Config:
-        from_attributes = True 
+        from_attributes = True
+
+# Update forward references for classes that reference other classes
+ProductWithRelated.model_rebuild()