Interview Q&A

Short answer: When & how to use it? Explicit loading means loading related data manually, after the main entity is loaded. Use when: You need full control over what and when to load You don’t want automatic lazy loading

Example code

var blog = context.Blogs.First(); context.Entry(blog) .Collection(b => b.Posts) .Load(); context.Entry(blog) .Reference(b => b.Owner) .Load(); ✅ Use .Reference().Load() for single navigation ✅ Use .Collection().Load() for collections

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: The N+1 problem occurs when: 1 query loads N parent entities N additional queries load related entities (1 per parent) Example (lazy loading): foreach (var blog in context.Blogs) { Console.WriteLine(blog.Owner.Name); // triggers a query for each blog } This causes N+1 queries, which can hurt performance significantly.

Explain a bit more

✅ Solution: Use eager loading with .Include() to fetch everything in one query. The N+1 problem occurs when: 1 query loads N parent entities N additional queries load related entities (1 per parent) Example (lazy loading): foreach (var blog in context.Blogs) { Console.WriteLine(blog.Owner.Name); // triggers a query for each blog } This causes N+1 queries, which can hurt performance significantly. ✅ Solution: Use eager loading with .Include() to fetch everything in one query.

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 can lazy loading lead to it? The N+1 problem occurs when: 1 query loads N parent entities N additional queries load related entities (1 per parent) Example (lazy loading): foreach (var blog in context.Blogs) { Console.WriteLine(blog.Owner.Name); // triggers a query for each blog } This causes N+1 queries, which can hurt performance significantly. ✅ Solution: Use eager loading with .Include() to fetch everything…

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: 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: By default, EF Core uses no automatic loading — it doesn’t lazy-load or eager-load relationships unless you: Use .Include() for eager loading Enable lazy loading proxies Use .Load() for explicit loading This default avoids unintended queries and promotes performance control. EF Core LINQ Queries & Querying

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: 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: Projection transforms entities into custom shapes, e.g., DTOs. var projected = context.Products

Example code

.Select(p => new { p.Name, p.Price }); Useful for: Reducing data load. Returning only needed fields. Mapping to custom types.

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.

Short answer: Stored procedures can be called via raw SQL or FromSqlRaw: var orders = context.Orders .FromSqlRaw("EXEC GetOrdersByCustomer @CustomerId = {0}", customerId) .ToList(); For non-query SPs, use Database.ExecuteSqlRaw().

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: Precompile frequently used queries to improve performance: private static readonly Func<MyDbContext, int, Product> _getProductById = EF.CompileQuery((MyDbContext ctx, int id) => ctx.Products.First(p => p.Id == id)); // Usage: var product = _getProductById(context, 5);

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: Enable logging in DbContext options: optionsBuilder .UseSqlServer(connectionString) .LogTo(Console.WriteLine, LogLevel.Information); Or configure logging in ASP.NET Core logging pipeline. Repository Pattern & Unit of Work

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: pplication. Pros: Decouples data access logic from business logic. Easier to mock/test. Encapsulates queries in a single place. Cons: EF Core’s DbContext already acts like a repository and unit of work. Can add unnecessary abstraction and boilerplate. May limit EF Core’s powerful querying features.

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: Why use it with EF Core (pros and cons)? Repository Pattern abstracts data access logic, exposing CRUD methods to the application. Pros: Decouples data access logic from business logic. Easier to mock/test. Encapsulates queries in a single place. Cons: EF Core’s DbContext already acts like a repository and unit of work. Can add unnecessary abstraction and boilerplate. May limit EF Core’s powerful querying features.

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: Unit of Work maintains a list of operations to be committed as a single transaction. EF Core’s DbContext implements Unit of Work, tracking changes and coordinating commits (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.