[D2C-37] 장바구니 화면 및 상품 제거/주문 진입 흐름 구현

apps/api/backend/api/routes/cart_items.py

@@ -5,9 +5,14 @@
 from backend.schemas.cart_item import (
     CartItemCreateRequest,
     CartItemDeleteResponse,
+    CartItemQuantityUpdateRequest,
     CartItemResponse,
 )
-from backend.services.cart_item_service import add_item_to_cart, remove_item_from_cart
+from backend.services.cart_item_service import (
+    add_item_to_cart,
+    remove_item_from_cart,
+    update_cart_item_quantity,
+)
 
 router = APIRouter(prefix="/carts", tags=["carts"])
 
@@ -29,4 +34,18 @@ def add_cart_item(cart_id: UUID, payload: CartItemCreateRequest) -> CartItemResp
 )
 def delete_cart_item(cart_id: UUID, cart_item_id: UUID) -> CartItemDeleteResponse:
     result = remove_item_from_cart(cart_id, cart_item_id)
-    return CartItemDeleteResponse(**result)
+    return CartItemDeleteResponse(**result)
+
+
+@router.patch(
+    "/{cart_id}/items/{cart_item_id}",
+    response_model=CartItemResponse,
+    status_code=status.HTTP_200_OK,
+)
+def patch_cart_item_quantity(
+    cart_id: UUID,
+    cart_item_id: UUID,
+    payload: CartItemQuantityUpdateRequest,
+) -> CartItemResponse:
+    item = update_cart_item_quantity(cart_id, cart_item_id, payload)
+    return CartItemResponse(**item)

apps/api/backend/schemas/cart.py

@@ -22,6 +22,7 @@ class CartItemSummaryResponse(BaseModel):
     cart_item_id: UUID
     product_id: UUID
     product_name: str
+    brand_name: str | None = None
     quantity: int
     unit_price: Decimal
     currency: str

apps/api/backend/schemas/cart_item.py

@@ -24,4 +24,8 @@ class CartItemResponse(BaseModel):
 class CartItemDeleteResponse(BaseModel):
     cart_item_id: UUID
     cart_id: UUID
-    message: str
+    message: str
+
+
+class CartItemQuantityUpdateRequest(BaseModel):
+    quantity: int = Field(ge=1, le=999)

apps/api/backend/services/cart_item_service.py

@@ -5,7 +5,10 @@
 from sqlalchemy import text
 
 from backend.db.connection import engine
-from backend.schemas.cart_item import CartItemCreateRequest
+from backend.schemas.cart_item import (
+    CartItemCreateRequest, 
+    CartItemQuantityUpdateRequest,
+)
 
 
 def add_item_to_cart(cart_id: UUID, payload: CartItemCreateRequest) -> dict[str, Any]:
@@ -235,4 +238,103 @@ def remove_item_from_cart(cart_id: UUID, cart_item_id: UUID) -> dict[str, Any]:
             "cart_item_id": deleted_item["cart_item_id"],
             "cart_id": deleted_item["cart_id"],
             "message": "Cart item removed successfully",
-        }
+        }
+
+def update_cart_item_quantity(
+    cart_id: UUID,
+    cart_item_id: UUID,
+    payload: CartItemQuantityUpdateRequest,
+) -> dict[str, Any]:
+    cart_query = text("""
+        SELECT
+            cart_id,
+            cart_status
+        FROM carts
+        WHERE cart_id = :cart_id
+          AND cart_status = 'active'
+        LIMIT 1
+    """)
+
+    item_query = text("""
+        SELECT
+            cart_item_id,
+            cart_id,
+            product_id,
+            unit_price,
+            currency
+        FROM cart_items
+        WHERE cart_id = :cart_id
+          AND cart_item_id = :cart_item_id
+        LIMIT 1
+    """)
+
+    update_query = text("""
+        UPDATE cart_items
+        SET
+            quantity = :quantity,
+            updated_at = CURRENT_TIMESTAMP
+        WHERE cart_id = :cart_id
+          AND cart_item_id = :cart_item_id
+        RETURNING
+            cart_item_id,
+            cart_id,
+            product_id,
+            quantity,
+            unit_price,
+            currency,
+            added_at,
+            updated_at
+    """)
+
+    with engine.begin() as connection:
+        cart = connection.execute(
+            cart_query,
+            {"cart_id": cart_id},
+        ).mappings().first()
+
+        if cart is None:
+            raise HTTPException(
+                status_code=status.HTTP_404_NOT_FOUND,
+                detail="Active cart not found",
+            )
+
+        item = connection.execute(
+            item_query,
+            {
+                "cart_id": cart_id,
+                "cart_item_id": cart_item_id,
+            },
+        ).mappings().first()
+
+        if item is None:
+            raise HTTPException(
+                status_code=status.HTTP_404_NOT_FOUND,
+                detail="Cart item not found",
+            )
+
+        updated_item = connection.execute(
+            update_query,
+            {
+                "cart_id": cart_id,
+                "cart_item_id": cart_item_id,
+                "quantity": payload.quantity,
+            },
+        ).mappings().first()
+
+        if updated_item is None:
+            raise HTTPException(
+                status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
+                detail="Failed to update cart item quantity",
+            )
+
+    return {
+        "cart_item_id": updated_item["cart_item_id"],
+        "cart_id": updated_item["cart_id"],
+        "product_id": updated_item["product_id"],
+        "quantity": updated_item["quantity"],
+        "unit_price": updated_item["unit_price"],
+        "currency": updated_item["currency"],
+        "added_at": updated_item["added_at"],
+        "updated_at": updated_item["updated_at"],
+        "message": "Cart item quantity updated successfully",
+    }

apps/api/backend/services/cart_service.py

@@ -106,6 +106,7 @@ def get_cart_detail(cart_id: UUID) -> dict[str, Any]:
             ci.cart_item_id,
             ci.product_id,
             p.product_name,
+            p.brand_name,
             ci.quantity,
             ci.unit_price,
             ci.currency,
@@ -154,6 +155,7 @@ def get_cart_detail(cart_id: UUID) -> dict[str, Any]:
                 "cart_item_id": row["cart_item_id"],
                 "product_id": row["product_id"],
                 "product_name": row["product_name"],
+                "brand_name": row["brand_name"],
                 "quantity": row["quantity"],
                 "unit_price": row["unit_price"],
                 "currency": row["currency"],