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Overview

The Product model represents items in the supermarket inventory. It includes pricing information, stock levels, and a relationship to the Category model for product classification.

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Class Definition

using System.ComponentModel.DataAnnotations.Schema;

namespace SupermarketWEB.Models
{
    public class Product
    {
        public int Id { get; set; }
        public string Name { get; set; }

        [Column(TypeName = "decimal(6,2)")]
        public decimal Price { get; set; }
        public int Stock { get; set; }
        public int CategoryId { get; set; }
        public Category? Category { get; set; }
    }
}

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Properties

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Id
int
required
Primary key and unique identifier for the product. Auto-generated by the database.
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Name
string
required
The product name or title displayed to customers and used in inventory management.
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Price
decimal
required
Product price with precision of 6 digits total and 2 decimal places. Stored as decimal(6,2) in the database, allowing values up to 9999.99.Column Attribute: [Column(TypeName = "decimal(6,2)")] ensures precise decimal storage without floating-point errors.
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Stock
int
required
Current inventory quantity available for sale. Used for stock management and availability checks.
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CategoryId
int
required
Foreign key reference to the Category table. Establishes the many-to-one relationship between products and categories.
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Category
Category
Navigation property to the related Category entity. Nullable to support lazy loading and optional eager loading scenarios.

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Data Annotations

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Column Type Specification

The Price property uses a column type annotation to ensure precise decimal handling: 
[Column(TypeName = "decimal(6,2)")]
public decimal Price { get; set; }
The decimal(6,2) type specification means:
  • 6: Total number of digits (precision)
  • 2: Number of digits after decimal point (scale)
  • Range: -9999.99 to 9999.99
This prevents floating-point arithmetic errors common with float or double types, which is critical for financial calculations.

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Relationships

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Category Relationship (Many-to-One)

Each product belongs to exactly one category: 
public int CategoryId { get; set; }      // Foreign key
public Category? Category { get; set; }  // Navigation property
Loading Related Data: 
// Load products with their categories
var products = await context.Products
    .Include(p => p.Category)
    .ToListAsync();

foreach (var product in products)
{
    Console.WriteLine($"{product.Name} - {product.Category.Name}");
}

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Usage Examples

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Creating a New Product

var product = new Product
{
    Name = "Organic Apples",
    Price = 3.99m,
    Stock = 150,
    CategoryId = 1  // Reference to Fruits category
};

context.Products.Add(product);
await context.SaveChangesAsync();

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Updating Stock

var product = await context.Products.FindAsync(productId);
if (product != null)
{
    product.Stock -= quantitySold;
    await context.SaveChangesAsync();
}

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Querying Products by Category

var categoryProducts = await context.Products
    .Where(p => p.CategoryId == categoryId)
    .OrderBy(p => p.Name)
    .ToListAsync();

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Low Stock Alert

var lowStockProducts = await context.Products
    .Include(p => p.Category)
    .Where(p => p.Stock < 10)
    .Select(p => new {
        p.Name,
        p.Stock,
        Category = p.Category.Name
    })
    .ToListAsync();

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Database Schema

When migrated to the database, the Product table has the following structure:
ColumnTypeNullableKey
IdintNoPrimary Key (Identity)
Namenvarchar(MAX)No
Pricedecimal(6,2)No
StockintNo
CategoryIdintNoForeign Key → Categories.Id
The Category navigation property does not create a database column. It’s used by Entity Framework for relationship mapping.

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Best Practices

  1. Price Precision: Always use decimal type for currency to avoid rounding errors
  2. Stock Validation: Implement business logic to prevent negative stock values
  3. Category Assignment: Ensure CategoryId references a valid Category before saving
  4. Eager Loading: Use .Include() when you know you’ll need the Category to avoid N+1 queries
  5. Null Checks: Always check if Category is null before accessing its properties if not using eager loading

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