Why should you care?

ShopNest cannot allow two products with the same SKU or orders referencing missing customers — constraints are the last line of defense.

See it live — copy this example

Paste into a .NET project with EF Core packages, then run with LocalDB/SQL Server (dotnet ef / dotnet run).

modelBuilder.Entity<Product>(e =>
{
    e.HasIndex(p => p.Sku).IsUnique();
    e.Property(p => p.Name).IsRequired();
    e.ToTable(t => t.HasCheckConstraint("CK_Product_Price", "Price > 0"));
});

modelBuilder.Entity<Order>(e =>
{
    e.HasOne(o => o.Customer)
        .WithMany(c => c.Orders)
        .HasForeignKey(o => o.CustomerId)
        .OnDelete(DeleteBehavior.Restrict);
});

What happened?

• Unique index on Sku blocks duplicates.
• Check constraint rejects non-positive prices.
• Restrict on CustomerId prevents deleting customers with orders.

Practice next

1. Add unique SKU and price check constraint via Fluent API.
2. Generate migration and verify CONSTRAINT lines in Up() SQL.
3. Attempt duplicate Sku insert and read SQL error.
4. Add filter unique index: HasIndex(p => p.Sku).IsUnique().HasFilter("[IsDeleted] = 0") for soft delete.
5. Use HasAlternateKey on Customer.Email for uniqueness without making it PK.

Remember

Constraints protect data at the database layer. Fluent API expresses indexes, checks, and FK rules. Unique SKU is a classic e-commerce constraint.

ShopNest SKU integrity

Duplicate SKU insert during bulk import fails at SQL unique index despite passing CSV validation.

Outcome: Catalog stays consistent for Flipkart-scale search indexing.