Add ItemPurchase model to track purchases

- Introduced a new `ItemPurchase` model to the SQL database, which includes fields for `id`, `item_id`, `user_id`, `quantity`, and `created_at`.
- Implemented foreign key relationships for `item_id` and `user_id` with cascade deletion.
- Added validation to ensure `quantity` is greater than or equal to 1.
- Default value for `created_at` set to the current timestamp in UTC format.

Author: maxmux-xyz

backend/app/models.py

@@ -1,4 +1,5 @@
 import uuid
+from datetime import datetime, timezone
 
 from pydantic import EmailStr
 from sqlmodel import Field, Relationship, SQLModel
@@ -92,6 +93,19 @@ class ItemsPublic(SQLModel):
     count: int
 
 
+# Database model, database table inferred from class name
+class ItemPurchase(SQLModel, table=True):
+    id: uuid.UUID = Field(default_factory=uuid.uuid4, primary_key=True)
+    item_id: uuid.UUID = Field(
+        foreign_key="item.id", nullable=False, ondelete="CASCADE"
+    )
+    user_id: uuid.UUID = Field(
+        foreign_key="user.id", nullable=False, ondelete="CASCADE"
+    )
+    quantity: int = Field(ge=1)
+    created_at: datetime = Field(default_factory=lambda: datetime.now(timezone.utc))
+
+
 # Generic message
 class Message(SQLModel):
     message: str