Interview Q&A

Short answer: Entity Framework Core (EF Core) is a modern, lightweight, cross-platform, open-source ORM (Object-Relational Mapper) for .NET. It allows developers to interact with databases using C# objects rather than SQL queries.

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: ORM is a technique that maps objects in code to relational database tables. EF Core implements ORM by mapping .NET classes (entities) to database tables using DbContext, DbSet, and conventions or Fluent API.

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: How does EF Core implement it? ORM is a technique that maps objects in code to relational database tables. EF Core implements ORM by mapping .NET classes (entities) to database tables using DbContext, DbSet, and conventions or Fluent API.

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: DbContext is the primary class for interacting with the database in EF Core.

Explain a bit more

It: Manages database connections Tracks changes to entities Provides methods for querying and saving data Configures models and relationships DbContext is the primary class for interacting with the database in EF Core. It: Manages database connections Tracks changes to entities Provides methods for querying and saving data Configures models and relationships

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: What responsibilities does it have? DbContext is the primary class for interacting with the database in EF Core. It: Manages database connections Tracks changes to entities Provides methods for querying and saving data Configures models and relationships

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: DbSet<T> represents a collection of entities of type T in the context. Each DbSet maps to a table in the database, where T is the type of the entity.

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: How does it map to database tables? DbSet<T> represents a collection of entities of type T in the context. Each DbSet maps to a table in the database, where T is the type of the entity.

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: 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: 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: 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.

Short answer: fter they are loaded from the database. This allows EF Core to generate the correct SQL INSERT, UPDATE, or DELETE statements when SaveChanges() is called.

Real-world example (ShopNest)

Read-only catalog pages use AsNoTracking() so EF Core does not spend time snapshotting entities you will never update.

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: Change tracking is the process by which EF Core keeps track of changes made to entities after they are loaded from the database. This allows EF Core to generate the correct SQL INSERT, UPDATE, or DELETE statements when SaveChanges() is called.

Real-world example (ShopNest)

Read-only catalog pages use AsNoTracking() so EF Core does not spend time snapshotting entities you will never update.

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: re monitored and persisted. Untracked queries: EF does not monitor the returned entities. re monitored and persisted. Untracked queries: EF does not monitor the returned entities. Faster, read-only ccess. Tracked (default): var user = context.Users.FirstOrDefault(); Untracked: var user = context.Users.AsNoTracking().FirstOrDefault(); re monitored and…… persisted. Untracked queries: EF does not monitor the returned…

Explain a bit more

entities. Faster, read-only ccess. Tracked (default): var user = context.Users.FirstOrDefault(); Untracked: var user = context.Users.AsNoTracking().FirstOrDefault(); re monitored and persisted. Untracked queries: EF does not monitor the returned entities. re monitored and persisted. Untracked queries: EF does not monitor the returned entities. Faster, read-only ccess. Tracked (default): var user = context.Users.FirstOrDefault(); Untracked: var user = context.Users.AsNoTracking().FirstOrDefault(); re monitored and persisted. Untracked queries: EF does not monitor the returned entities. Faster, read-only ccess. Tracked (default):…

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: Tracked queries: EF Core tracks entities returned from the query. Changes to them are monitored and persisted. Untracked queries: EF does not monitor the returned entities. Faster, read-only access. Tracked (default): var user = context.Users.FirstOrDefault(); Untracked: var user = context.Users.AsNoTracking().FirstOrDefault();

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: .AsNoTracking() tells EF Core not to track entities in the returned query.

Explain a bit more

✅ Use when: Read-only operations Improving performance for large queries Preventing memory overhead of tracking var users = context.Users.AsNoTracking().ToList(); .AsNoTracking() tells EF Core not to track entities in the returned query. .AsNoTracking() tells EF Core not to track entities in the returned query. ✅ Use when: Read-only operations Improving performance for large queries Preventing memory overhead of tracking

Example code

var users = context.Users.AsNoTracking().ToList(); .AsNoTracking() tells EF Core not to track entities in the returned query. .AsNoTracking() tells EF Core not to track entities in the returned query. ✅ Use when: Read-only operations Improving performance for large queries Preventing memory overhead of tracking Example: var users = context.Users.AsNoTracking().ToList(); .AsNoTracking() tells EF Core not to track entities in the returned query. ✅ Use when: Read-only operations Improving performance for large queries Preventing memory overhead of tracking Example: var users = context.Users.AsNoTracking().ToList();

Real-world example (ShopNest)

Read-only catalog pages use AsNoTracking() so EF Core does not spend time snapshotting entities you will never update.

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: When to use it? .AsNoTracking() tells EF Core not to track entities in the returned query. ✅ Use when: Read-only operations Improving performance for large queries Preventing memory overhead of tracking

Example code

var users = context.Users.AsNoTracking().ToList();

Real-world example (ShopNest)

Read-only catalog pages use AsNoTracking() so EF Core does not spend time snapshotting entities you will never update.

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.