Interview Q&A

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.

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 in one query.

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).

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.

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

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.

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

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

• 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.

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.

• 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.

• Inner join example:

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 };

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)

});

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

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: Projection transforms entities into custom shapes, e.g., DTOs. var projected = context.Products .Select(p =&gt; new { p.Name, p.Price }); Useful for: Reducing data load. Returning only needed fields. Mapping to custom types.

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

• 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.

Answer: Use .Skip() and .Take() for pagination: var page2 = context.Products .OrderBy(p =&gt; p.Id) .Skip(10) // Skip first 10 .Take(10) // Take next 10 .ToList();

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

Answer: (Skip, Take) Use .Skip() and .Take() for pagination: var page2 = context.Products .OrderBy(p =&gt; p.Id) .Skip(10) // Skip first 10 .Take(10) // Take next 10 .ToList();

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

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

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

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

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

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().

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

• 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);

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 &amp; Unit of Work

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

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.

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.

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()).

What interviewers expect

• A clear definition tied to EF Core in Entity Framework Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production Entity Framework Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in Entity Framework Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.

• Generic repository provides CRUD for all entity types.
• Advantages:
• Reusable and reduces boilerplate.
• Simple for basic CRUD.
• Disadvantages:
• Can become too generic, losing flexibility for complex queries.
• May leak EF Core specifics or cause over-abstraction.
• Sometimes custom repositories per aggregate are better.