Entity Framework  

Mastering .NET Interviews – Part 6: Entity Framework & Data Access

📌 Series Context: This is the sixth article in the 10‑part series covering the most important areas of .NET interview preparation. In Part 1, we introduced the .NET ecosystem. In Part 2, we covered C# fundamentals. In Part 3, we explored advanced C# features. In Part 4, we discussed ASP.NET MVC. In Part 5, we focused on ASP.NET Core. Now, we’ll dive into Entity Framework (EF) and Data Access.

Why Entity Framework?

Entity Framework (EF) is Microsoft's Object-Relational Mapper (ORM). It simplifies database access by allowing developers to work with C# objects instead of SQL queries. Interviewers often ask about EF Core, LINQ, migrations, and performance tuning.

Approaches in Entity Framework

Database-First

  • Generate models from an existing database.

Code-First

  • Define models in C# and generate the database schema.

Model-First

  • Design models visually, then generate code and the database.

👉 Interview Tip: Be ready to explain the advantages and disadvantages of each approach.

Example: Patient Entity

public class Patient
{
    public int Id { get; set; }

    public string Name { get; set; }

    public int Age { get; set; }

    public string Disease { get; set; }
}

DbContext

public class HospitalContext : DbContext
{
    public DbSet<Patient> Patients { get; set; }

    public DbSet<Staff> Staff { get; set; }

    public DbSet<Invoice> Invoices { get; set; }
}

👉 DbContext acts as a bridge between C# objects and the database.

LINQ Queries

Entity Framework uses LINQ for querying data.

var patients = context.Patients
                      .Where(p => p.Age > 40)
                      .OrderBy(p => p.Name)
                      .ToList();

👉 Interview Tip: Be ready to write LINQ queries on the spot.

Migrations

Migrations allow schema changes without dropping the database.

dotnet ef migrations add InitialCreate
dotnet ef database update

👉 Interview Tip: Be ready to explain how migrations help in agile development.

Transactions

EF supports transactions for multiple operations.

using var transaction = context.Database.BeginTransaction();

try
{
    context.Patients.Add(new Patient { Name = "John" });
    context.SaveChanges();

    context.Invoices.Add(new Invoice
    {
        PatientId = 1,
        Amount = 500
    });

    context.SaveChanges();

    transaction.Commit();
}
catch
{
    transaction.Rollback();
}

Common Interview Questions (Part 6)

  • What is the difference between Database-First and Code-First approaches?

  • How does DbContext work in EF?

  • Explain LINQ queries in EF.

  • What are Migrations and why are they important?

  • How do you handle transactions in EF?

  • How do you improve performance in EF Core?

Conclusion

In this sixth part, we covered:

  • Entity Framework approaches (Database-First, Code-First, and Model-First).

  • DbContext and how it maps objects to tables.

  • LINQ queries for data access.

  • Migrations for schema evolution.

  • Transactions for safe multi-operation workflows.

This foundation prepares you for Part 7, where we'll explore Web API & Microservices—covering REST principles, API versioning, and microservices architecture in .NET.

Summary

Entity Framework simplifies database operations by allowing developers to work with C# objects instead of writing raw SQL. Understanding EF approaches, DbContext, LINQ queries, migrations, and transactions is essential for building maintainable data-driven applications and performing well in .NET technical interviews.

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