Interview Q&A

Short answer: context.Entry(entity).State = EntityState.Detached; This is helpful when: You’re updating data without reloading it Working with disconnected scenarios (e.g., APIs)

Example code

Use the Entry() method: context.Entry(entity).State = EntityState.Modified;

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 optimistic concurrency vs pessimistic concurrency? Optimistic concurrency: Assumes that conflicts are rare. EF checks for changes before saving using concurrency tokens. Pessimistic concurrency: Locks records in the DB to prevent other updates (not supported out-of-the-box in EF Core). EF Core supports optimistic concurrency using [ConcurrencyCheck] or [Timestamp].

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.

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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 supports the standard types of relationships: One-to-One (1:1) – One entity has one related entity. One-to-Many (1:N) – One entity relates to many others. Many-to-Many (M:N) – Many entities relate to many others. Each of these can be configured in EF Core using navigation properties and Fluent API or Data Annotations.

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: Example using Fluent API: modelBuilder.Entity<User>() .HasOne(u => u.Profile) .WithOne(p => p.User) .HasForeignKey<Profile>(p => p.UserId); Or with data annotations: public class Profile

Example code

{ [Key, ForeignKey("User")] public int UserId { get; set; }
public User User { get; set; }
} Requires a unique foreign key. EF assumes optional by default unless marked as required.

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: Fluent API: modelBuilder.Entity<Blog>() .HasMany(b => b.Posts) .WithOne(p => p.Blog) .HasForeignKey(p => p.BlogId); Data annotations: public class Post { public int BlogId { get; set; } [ForeignKey("BlogId")] public Blog Blog { get; set; } } A foreign key exists in the many-side entity (Post). EF infers this relationship from navigation + FK.

Example code

Fluent API: modelBuilder.Entity<Blog>() .HasMany(b => b.Posts) .WithOne(p => p.Blog) .HasForeignKey(p => p.BlogId); Data annotations: public class Post
{
public int BlogId { get; set; } [ForeignKey("BlogId")] public Blog Blog { get; set; }
} A foreign key exists in the many-side entity (Post). EF infers this relationship from navigation + FK.

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: In EF Core 5.0+, you can define many-to-many relationships without an explicit join entity: public class Student

Example code

{
public ICollection<Course> Courses { get; set; }
}
public class Course
{
public ICollection<Student> Students { get; set; }
} EF will automatically create a join table CourseStudent behind the scenes. If you want to customize the join table, define a join entity explicitly.

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: join table maps a many-to-many relationship. In EF Core: ✅ Auto-created (EF Core 5+): If you define many-to-many with ICollection<T>, EF creates the join table. {

Example code

public int StudentId { get; set; }
public Student Student { get; set; }
public int CourseId { get; set; }
public Course Course { get; set; }
} nd configure with 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 to represent them in EF Core? A join table maps a many-to-many relationship. In EF Core: ✅ Auto-created (EF Core 5+): If you define many-to-many with ICollection<T>, EF creates the join table. 🛠 Manual (custom join entity): public class StudentCourse

Example code

{
public int StudentId { get; set; }
public Student Student { get; set; }
public int CourseId { get; set; }
public Course Course { get; set; }
} And configure with 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 to define them via annotations & Fluent API?

Explain a bit more

Primary Key (PK): Unique identifier of a record. Foreign Key (FK): A field that references a PK in another table. Data Annotations: [Key] public int Id { get; set; } [ForeignKey("Blog")] public int BlogId { get; set; } Fluent API: modelBuilder.Entity<Post>() .HasKey(p => p.Id); modelBuilder.Entity<Post>() .HasOne(p => p.Blog) .WithMany(b => b.Posts) .HasForeignKey(p => p.BlogId);

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 shadow property is a property not defined in the .NET class but exists in the EF model.

Example code

modelBuilder.Entity<Post>() .HasOne<Blog>() .WithMany() .HasForeignKey("BlogId"); // BlogId is a shadow FK if not defined in class EF tracks it internally but you can't access it in C# code directly.

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: In Fluent API: Required: .HasRequired(p => p.Blog) Optional: .HasOne(p => p.Blog) .WithMany() .IsRequired(false); EF infers: Reference type (e.g., Blog) → optional by default Non-nullable value type FK (e.g., int BlogId) → required Entity Framework Core – Lazy vs Eager vs Explicit Loading

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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: Loading Type Pros Cons Eager Fewer queries, good for large data sets Loads everything even if not used Lazy Loads only when needed Risk of N+1 queries, more round-trips Explicit Fine-grained control More code complexity ✅ Eager is best for performance when you know you'll need related data. ❌ Lazy can hurt performance unless used carefully (e.g., in UI apps).

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: Yes. You can disable lazy loading globally: options.UseLazyLoadingProxies(false); Or don't install the proxy package at all. You can also disable it for specific navigation properties by not making them virtual. Yes. You can disable lazy loading globally: options.UseLazyLoadingProxies(false); Or don't install the proxy package at… all. You can also disable…… it for specific navigation properties by not making them…

Explain a bit more

virtual. Yes. You can disable lazy loading globally: options.UseLazyLoadingProxies(false); Or don't install the proxy package at all. You can also disable it for specific navigation properties by not making them virtual. Yes. You can disable lazy loading globally: options.UseLazyLoadingProxies(false); Or don't install the proxy package at… all. You can also disable it for specific navigation properties by not making them virtual.

Real-world example (ShopNest)

Loading orders with items uses .Include(o => o.Items). Without Include, listing 50 orders can trigger 50 extra queries (N+1).

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? Yes. You can disable lazy loading globally: options.UseLazyLoadingProxies(false); Or don't install the proxy package at all. You can also disable it for specific navigation properties by not making them virtual.

Real-world example (ShopNest)

Loading orders with items uses .Include(o => o.Items). Without Include, listing 50 orders can trigger 50 extra queries (N+1).

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 translates LINQ queries into SQL using expression trees. Only supported LINQ operators and expressions can be translated. Limitations: Certain C# methods or complex expressions cannot be translated and cause runtime exceptions. Client-side evaluation may occur, which can hurt performance. Use .AsEnumerable() to switch to client-side processing intentionally.

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 limitations are there? EF Core translates LINQ queries into SQL using expression trees. Only supported LINQ operators and expressions can be translated. Limitations: Certain C# methods or complex expressions cannot be translated and cause runtime exceptions. Client-side evaluation may occur, which can hurt performance. Use .AsEnumerable() to switch to client-side processing intentionally.

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: IQueryable<T>: Represents a query against the data source. Query is translated to SQL and executed on the database. Supports deferred execution. IEnumerable<T>: Represents an in-memory collection. LINQ operators execute in memory. Usually results after the query has executed and data is loaded.

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: Inner join

Example code

var query = from c in context.Customers join o in context.Orders on c.Id equals o.CustomerId select new { c.Name, o.OrderDate }; Left join (using DefaultIfEmpty()): var query = from c in context.Customers join o in context.Orders on c.Id equals o.CustomerId into orders from o in orders.DefaultIfEmpty() select new { c.Name, OrderDate = o != null ? o.OrderDate : (DateTime?)null };

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: var groupedData = context.Orders .GroupBy(o => o.CustomerId) .Select(g => new { CustomerId = g.Key, TotalOrders = g.Count(), TotalAmount = g.Sum(o => o.Amount), MaxAmount = g.Max(o => o.Amount), MinAmount = g.Min(o => o.Amount) });

Example code

var groupedData = context.Orders .GroupBy(o => o.CustomerId) .Select(g => new { CustomerId = g.Key, TotalOrders = g.Count(), TotalAmount = g.Sum(o => o.Amount), MaxAmount = g.Max(o => o.Amount), MinAmount = g.Min(o => o.Amount) });

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: Filtering: var filtered = context.Products.Where(p => p.Price > 100); Ordering: var ordered = context.Products .OrderBy(p => p.Category) .ThenByDescending(p => p.Price);

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: First(): Returns the first element, throws if none found. FirstOrDefault(): Returns first element or default (null) if none. Single(): Returns the single element, throws if zero or more than one. SingleOrDefault(): Returns the single element or default if none; throws if more than one.

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 .Skip() and .Take() for pagination: var page2 = context.Products .OrderBy(p => p.Id) .Skip(10) // Skip first 10 .Take(10) // Take next 10 .ToList(); Use .Skip() and .Take() for pagination: var page2 = context.Products .OrderBy(p => p.Id) .Skip(10) // Skip first 10 .Take(10) // Take next 10 .ToList(); Real-world example… (ShopNest) ShopNest’s order…… service uses EF Core to save an Order and its line items in one…

Explain a bit more

SaveChangesAsync() call inside a transaction. Use .Skip() and .Take() for pagination: var page2 = context.Products .OrderBy(p => p.Id) .Skip(10) // Skip first 10 .Take(10) // Take next 10 .ToList(); Use .Skip() and .Take() for pagination: var page2 = context.Products .OrderBy(p => p.Id) .Skip(10) // Skip first 10 .Take(10) // Take next 10 .ToList(); 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: (Skip, Take) Use .Skip() and .Take() for pagination: var page2 = context.Products .OrderBy(p => p.Id) .Skip(10) // Skip first 10 .Take(10) // Take next 10 .ToList();

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 FromSqlRaw() or FromSqlInterpolated(): var products = context.Products .FromSqlRaw("SELECT * FROM Products WHERE Price > {0}", 100) .ToList(); Use FromSqlRaw() or FromSqlInterpolated(): var products = context.Products .FromSqlRaw("SELECT * FROM Products WHERE Price > {0}", 100) .ToList(); Use FromSqlRaw() or FromSqlInterpolated(): var products = context.

Explain a bit more

Products .FromSqlRaw("SELECT * FROM Products WHERE Price > {0}", 100) .ToList(); Use FromSqlRaw() or FromSqlInterpolated(): var products = context.Products .FromSqlRaw("SELECT * FROM Products WHERE Price > {0}", 100) .ToList();

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: (FromSqlRaw, etc.) Use FromSqlRaw() or FromSqlInterpolated(): var products = context.Products .FromSqlRaw("SELECT * FROM Products WHERE Price > {0}", 100) .ToList();

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.