Interview Q&A

Short answer: Entities are .NET classes that represent database tables. Each property in the entity maps to a column. EF Core uses conventions or Fluent API to configure the mappings.

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: POCO (Plain Old CLR Object) is a simple class without any dependency on EF Core or any base class. EF Core uses POCOs as entities for data modeling.

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Navigation properties allow navigation from one entity to related entities. They define relationships (one-to-one, one-to-many, many-to-many). Example: public class Order

Example code

{
public int Id { get; set; }
public Customer Customer { get; set; } // Navigation property
}

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Scalar: Simple types like int, string, DateTime Complex: Nested objects mapped to multiple columns (Value objects) Shadow: Properties not defined in the .NET class but tracked by EF Core

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: LINQ (Language Integrated Query) lets you query collections using C# syntax. LINQ to Entities is LINQ querying against the EF Core model, translated to SQL and executed in the database.

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: What is “LINQ to Entities”? LINQ (Language Integrated Query) lets you query collections using C# syntax. LINQ to Entities is LINQ querying against the EF Core model, translated to SQL and executed in the database.

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: // Create context.Users.Add(new User { Name = "John" }); context.SaveChanges(); // Read var user = context.Users.FirstOrDefault(u => u.Id == 1); // Update user.Name = "Jane"; context.SaveChanges(); // Delete context.Users.Remove(user); context.SaveChanges();

Example code

// Create context.Users.Add(new User { Name = "John" }); context.SaveChanges(); // Read var user = context.Users.FirstOrDefault(u => u.Id == 1); // Update user.Name = "Jane"; context.SaveChanges(); // Delete context.Users.Remove(user); context.SaveChanges();

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Productivity via abstraction from SQL Cross-platform support Strongly-typed LINQ queries Migration support Tracks changes automatically Works well with dependency injection

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: May generate inefficient SQL for complex queries Learning curve for advanced features Less control over fine-tuned SQL performance Not ideal for high-performance bulk operations Entity Framework Core – Schema Design & Migrations Interview Questions

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Code First is an EF Core approach where you define your database schema using C# classes, and EF Core generates the database from your code. ✅ Advantages: Full control via C# code (POCOs) Easily version-controlled Supports migrations to handle schema evolution Works well with Domain-Driven Design 📌 When to use: When you're starting a new project or prefer designing schema in code.

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Advantages and when to use it Code First is an EF Core approach where you define your database schema using C# classes, and EF Core generates the database from your code. ✅ Advantages: Full control via C# code (POCOs) Easily version-controlled Supports migrations to handle schema evolution Works well with Domain-Driven Design 📌 When to use: When you're starting a new project or prefer designing schema in code.

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Database First involves generating C# entity classes and a DbContext from an existing database. ✅ Pros: Quick start if the DB already exists Ensures model aligns with legacy databases ❌ Cons: Harder to version control Schema changes must be manually re-scaffolded 📌 When to use: For integrating with existing databases or legacy systems.

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use‑cases and pros and cons Database First involves generating C# entity classes and a DbContext from an existing database. ✅ Pros: Quick start if the DB already exists Ensures model aligns with legacy databases ❌ Cons: Harder to version control Schema changes must be manually re-scaffolded 📌 When to use: For integrating with existing databases or legacy systems.

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Model First allows creating a database model using a designer (EDMX file), then generating both the database and code from that model. ⚠ EF Core does not support Model First. This approach was available in EF6 with Visual Studio tooling.

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Is it used in EF Core? Model First allows creating a database model using a designer (EDMX file), then generating both the database and code from that model. ⚠ EF Core does not support Model First. This approach was available in EF6 with Visual Studio tooling.

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use the CLI or Package Manager Console: dotnet ef dbcontext scaffold "YourConnectionString" Microsoft.EntityFrameworkCore.SqlServer -o Models OR Scaffold-DbContext "YourConnectionString" Microsoft.EntityFrameworkCore.SqlServer -OutputDir Models ✅ It generates: Entity classes DbContext class Mappings based on database schema

Real-world example (ShopNest)

ShopNest registers AppDbContext as scoped. One HTTP request = one context. Never inject it as a singleton.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: EF Core uses migrations to track and apply schema changes: You modify your C# models. Use Add-Migration to create a migration class. Use Update-Database to apply the changes to the DB. EF Core compares the model to the current schema to generate SQL.

Real-world example (ShopNest)

When ShopNest adds a DiscountCode column, you create a migration, review the SQL, then apply it on staging before production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: 🧩 Data Annotations (in the entity class): [Table("Users")] public class User

Example code

{ [Key] public int Id { get; set; } [Column("UserName")] public string Name { get; set; }
} 🧠 Fluent API (in OnModelCreating): modelBuilder.Entity<User>() .ToTable("Users") .HasKey(u => u.Id); modelBuilder.Entity<User>() .Property(u => u.Name) .HasColumnName("UserName"); 📌 Fluent API is more powerful and flexible, preferred for complex configurations.

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Migrations in EF Core are a way to: Track schema changes over time Apply those changes to the database 📦 Basic commands: Add-Migration MigrationName Update-Database Remove-Migration Script-Migration 🔄 Migrations are classes containing Up() and Down() methods (for applying and reverting changes). 📌 They are essential for schema versioning in Code First. Entity Framework Core – Migrations Interview Questions

Real-world example (ShopNest)

When ShopNest adds a DiscountCode column, you create a migration, review the SQL, then apply it on staging before production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: How are they used in Code First? Migrations in EF Core are a way to: Track schema changes over time Apply those changes to the database 📦 Basic commands: Add-Migration MigrationName Update-Database Remove-Migration Script-Migration 🔄 Migrations are classes containing Up() and Down() methods (for applying and reverting changes). 📌 They are essential for schema versioning in Code First. Entity Framework Core –…

Real-world example (ShopNest)

When ShopNest adds a DiscountCode column, you create a migration, review the SQL, then apply it on staging before production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: dd-Migration MigrationName This creates a migration file with Up() and Down() methods, and a snapshot of the current model.

Real-world example (ShopNest)

When ShopNest adds a DiscountCode column, you create a migration, review the SQL, then apply it on staging before production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: (e.g. Add-Migration) Use one of the following commands: .NET CLI: dotnet ef migrations add MigrationName Package Manager Console: Add-Migration MigrationName This creates a migration file with Up() and Down() methods, and a snapshot of the current model.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: pply the migration to your database using: .NET CLI: dotnet ef database update Package Manager Console: Update-Database EF Core translates your model changes into SQL and executes them against the database.

Real-world example (ShopNest)

When ShopNest adds a DiscountCode column, you create a migration, review the SQL, then apply it on staging before production.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: (e.g. Update-Database) Apply the migration to your database using: .NET CLI: dotnet ef database update Package Manager Console: Update-Database EF Core translates your model changes into SQL and executes them against the database.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: A migration snapshot is a C# file (e.g., ModelSnapshot.cs) automatically created by EF Core. It represents the current model state. EF uses it to compare changes in future migrations. Located in the Migrations folder, named like [YourDbContext]ModelSnapshot.cs.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.