When modeling real-world domains in C#, nullable types (string?, DateTime?, bool?, etc.) aren’t just syntax sugar; they’re essential for accurately representing optional data, enforcing business rules, and improving database interactions.

1. Better Domain Clarity

Nullable types help distinguish between:

• "Zero" vs. "Unknown" – int? score = null (not taken) vs. score = 0 (actual zero)
• "Not applicable" vs. "False" – bool? IsApproved = null (pending) vs. false (rejected)
• "Missing data" vs. "Empty string" – string? comment = null (not provided) vs. "" (explicitly blank)

Example (E-Commerce):

public class Product { 
 public required string Name { get; set; } 
 public decimal Price { get; set; } 
 public string? Description { get; set; } // Optional 
 public int? StockCount { get; set; } // Null = not tracked 
 public DateTime? DiscontinuedDate { get; set; } // Null = still active 
} 

2. Cleaner ORM & Database Mapping

Relational databases use NULL extensively, and C# nullables ensure seamless ORM behavior with:

• EF Core / Dapper / NHibernate – Properly maps NULL ↔ null without "magic values" (like -1 or DateTime.MinValue)
• Accurate schema generation – NOT NULL vs. NULL columns align with C# model requirements
• Correct query handling – WHERE column IS NULL works as expected

Example (Employee DB):

public class Employee { 
 public int Id { get; set; } 
 public required string Name { get; set; } 
 public DateTime? TerminationDate { get; set; } // Null = still employed 
 public decimal? Bonus { get; set; } // Null = not eligible 
} 
→ EF Core generates the right NULL-allowed columns.

3. Key Takeaways

• Use T? for "optional" domain data (missing, unknown, or N/A states).
• Combine with the required to enforce mandatory fields at compile time.
• Improves ORM reliability – No more hidden InvalidOperationException from unexpected NULLs.

Result? More expressive domain models, fewer bugs, and database mappings that actually reflect real-world scenarios.