Persistent Systems .NET Full Stack Interview Questions & Answers
Curated interview practice questions with answers. These are practice scenarios, not a verified list of past interview questions.
About Persistent Systems hiring for .NET Full Stack roles
Persistent Systems is an Indian technology services company focused on software product engineering, digital transformation, cloud and data services. It serves clients in banking, healthcare, life sciences and software. In India it hires for software engineers, quality engineers, data engineers and analysts, often through campus drives with coding-focused assessments.
For .NET Full Stack roles, this Persistent Systems practice set focuses most on SQL Server and T-SQL (5), Angular and React Front End (4), LINQ, Collections and Generics (4), Async Programming and Multithreading (4). It has 11 easy, 16 medium, 3 hard questions, so you can start easy and work up to the harder ones.
Company type
IT services
Headquarters
Pune, India
Main India offices
Pune, Nagpur, Bengaluru, Hyderabad, Goa
Persistent Systems .NET Full Stack interview process
Online assessment (aptitude + coding)
Technical round 1
Technical round 2
HR round
Typical pattern based on public candidate experiences. Rounds vary by role, team and year.
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01
Angular or React with ASP.NET Core: how do you choose?
Angular is a complete framework with routing, forms, HTTP, dependency injection and TypeScript built in, which suits large enterprise apps and teams that want strong conventions. React is a UI library with a large ecosystem, giving more freedom to pick routing and state tools, and is popular in product startups. Both work equally well with an ASP.NET Core API. Choose based on team skills, project size and the company's existing stack.
HashSet<T> stores unique values with O(1) average lookup, add and remove. Use it when you need fast membership checks, such as checking if an email already exists in a batch of 1 lakh records, or to remove duplicates. It also supports set operations like UnionWith, IntersectWith and ExceptWith. It does not keep insertion order or allow index access; use SortedSet<T> if you need sorted unique values.
Interpolation {{ value }} shows component data in the template. Property binding [src]="imageUrl" sets an element or child property. Event binding (click)="save()" calls a component method on a DOM event. Two-way binding [(ngModel)]="name" combines property and event binding so the input and the field stay in sync. The first two flow from component to view, event binding flows from view to component.
WHERE filters individual rows before grouping and cannot use aggregate functions. HAVING filters groups after GROUP BY and can use aggregates like COUNT or SUM. For example, WHERE City = 'Pune' keeps only Pune rows, then GROUP BY DepartmentId HAVING COUNT(*) > 10 keeps departments with more than 10 such employees. Put non-aggregate conditions in WHERE so fewer rows are grouped, which is faster.
05
What does ConfigureAwait(false) do and is it needed in ASP.NET Core?
By default await captures the current SynchronizationContext and resumes on it. ConfigureAwait(false) tells the runtime it can resume on any thread pool thread, which avoids deadlocks in UI and old ASP.NET apps and slightly reduces overhead. ASP.NET Core has no SynchronizationContext, so it is not required in application code there. It is still recommended in general-purpose libraries that might be used by WPF or WinForms apps.
06
A read-only product listing endpoint in EF Core uses a lot of memory and CPU. What simple change helps, and why?
By default, EF Core tracks every entity it loads so it can detect changes on SaveChanges, which costs memory and CPU. AsNoTracking tells EF Core not to track the results, making read-only queries faster and lighter. Use it for lists, reports and GET endpoints where you will not update the data. AsNoTrackingWithIdentityResolution avoids duplicate instances of the same entity in results while still skipping tracking.
07
Write a stored procedure that transfers money between accounts with TRY-CATCH and a transaction.
CREATE OR ALTER PROCEDURE usp_Transfer @From INT, @To INT, @Amt DECIMAL(18,2)
AS
BEGIN
SET NOCOUNT ON;
SET XACT_ABORT ON;
BEGIN TRY
BEGIN TRAN;
UPDATE Accounts SET Balance = Balance - @Amt
WHERE Id = @From AND Balance >= @Amt;
IF @@ROWCOUNT = 0 THROW 50001, 'Insufficient balance', 1;
UPDATE Accounts SET Balance = Balance + @Amt WHERE Id = @To;
COMMIT;
END TRY
BEGIN CATCH
IF @@TRANCOUNT > 0 ROLLBACK;
THROW;
END CATCH
END
08
Write a recursive CTE that lists an employee hierarchy with levels.
WITH Org AS (
SELECT Id, Name, ManagerId, 0 AS Lvl
FROM Employees
WHERE ManagerId IS NULL -- anchor: CEO
UNION ALL
SELECT e.Id, e.Name, e.ManagerId, o.Lvl + 1
FROM Employees e
JOIN Org o ON e.ManagerId = o.Id -- recursive part
)
SELECT REPLICATE(' ', Lvl) + Name AS Hierarchy, Lvl
FROM Org
OPTION (MAXRECURSION 100);
The anchor query runs once and the recursive part repeats until no new rows are found.
09
What is the difference between a Task and a Thread?
A Thread is an OS-level execution unit with its own stack, costly to create. A Task is a higher-level promise of work that may or may not use a thread; I/O tasks often use no thread while waiting, and CPU tasks run on pooled threads. Tasks support return values, continuations, cancellation, exceptions and composition with WhenAll. In modern .NET you almost always use Tasks rather than creating threads manually.
10
What is the difference between a static class and a singleton?
A static class cannot be instantiated, cannot implement interfaces and is initialised by the runtime; it suits stateless helpers like Math. A singleton is a normal class with exactly one instance, so it can implement interfaces, be passed as a parameter and be mocked in tests. In ASP.NET Core, you rarely write a singleton by hand; you register the class with AddSingleton and let the DI container manage its lifetime.
11
Explain eager, lazy and explicit loading in EF Core.
Eager loading fetches related data in the same query using Include and ThenInclude, for example orders with their items. Lazy loading loads a navigation property automatically the first time you access it, requiring proxies and virtual properties; it is convenient but easily causes N+1 queries. Explicit loading loads a navigation on demand with Entry(order).Collection(o => o.Items).LoadAsync(). Projection with Select is often better than all three.
12
How does EF Core handle many-to-many relationships?
Since EF Core 5, you can define collection navigations on both sides, such as Student.Courses and Course.Students, and EF Core creates a hidden join table automatically. If the join needs extra data, like EnrolledOn or Grade, create an explicit join entity Enrollment with two foreign keys and configure it with UsingEntity or two one-to-many relationships. Querying works naturally with Include or projections through the navigations.
13
What are record types and when would you use them?
Records are reference types (or record struct for value types) designed for immutable data. The compiler generates value-based equality, a readable ToString, a deconstructor and support for with-expressions that create a modified copy. A positional record is one line: public record Order(int Id, decimal Total). They suit DTOs, API responses, events and value objects, but not EF Core entities that need change tracking by identity.
A view is a saved SELECT query that acts like a virtual table; it simplifies complex joins and can restrict which columns users see, but by default it stores no data. An indexed view has a unique clustered index, so SQL Server physically stores and maintains its results, which speeds up heavy aggregations. The cost is slower writes on base tables, and it requires SCHEMABINDING and deterministic expressions.
15
Write custom middleware that logs how long each request takes.
public class TimingMiddleware(RequestDelegate next, ILogger<TimingMiddleware> logger)
{
public async Task InvokeAsync(HttpContext context)
{
var sw = Stopwatch.StartNew();
await next(context);
sw.Stop();
logger.LogInformation("{Method} {Path} -> {Status} in {Ms} ms",
context.Request.Method, context.Request.Path,
context.Response.StatusCode, sw.ElapsedMilliseconds);
}
}
// Program.cs
app.UseMiddleware<TimingMiddleware>();
Code before next runs on the request, code after it runs on the response.
16
What are services and dependency injection in Angular?
A service is a class, marked @Injectable, that holds logic or data shared across components, such as API calls, authentication or a cart. Angular's DI creates the service and provides it to components that request it in the constructor or with the inject() function. With providedIn: 'root', one shared instance exists for the whole app. This keeps components focused on UI and makes logic easy to test.
17
Write a BackgroundService that cleans expired OTPs every 5 minutes.
public class OtpCleanupService(IServiceScopeFactory scopes) : BackgroundService
{
protected override async Task ExecuteAsync(CancellationToken ct)
{
using var timer = new PeriodicTimer(TimeSpan.FromMinutes(5));
while (await timer.WaitForNextTickAsync(ct))
{
using var scope = scopes.CreateScope();
var db = scope.ServiceProvider.GetRequiredService<AppDbContext>();
await db.Otps.Where(o => o.ExpiresAt < DateTime.UtcNow).ExecuteDeleteAsync(ct);
}
}
}
// builder.Services.AddHostedService<OtpCleanupService>();
A scope is created because DbContext is scoped while hosted services are singletons.
18
Why should we hire you as a .NET full stack developer?
I can contribute on both sides of a feature: I have built ASP.NET Core APIs with EF Core and SQL Server, and front ends in Angular and React, and deployed them myself. I write clean, tested code and I am comfortable reading logs and execution plans when things break. I learn quickly, ask questions early and take ownership, so you can give me a module and trust that it will be completed properly.
19
What is the difference between DELETE, TRUNCATE and DROP?
DELETE removes rows one by one, supports WHERE, fires triggers and is fully logged, so it is slower on big tables. TRUNCATE removes all rows by deallocating pages, is minimally logged, resets identity values and cannot have WHERE; it fails if foreign keys reference the table. DROP removes the whole table including structure, indexes and permissions. In SQL Server, both DELETE and TRUNCATE can be rolled back inside a transaction.
20
You are designing a type to hold a 2D point used millions of times in a calculation. Struct or class?
A struct is a good fit because the point is small, logically a single value and created in huge numbers. Structs avoid heap allocation and GC pressure when stored in arrays or locals. Make it a readonly struct so it is immutable and avoids defensive copies. Choose a class instead if the type is large, needs inheritance, or is frequently boxed through interfaces, since copying and boxing remove the benefit.
21
Explain the transient, scoped and singleton service lifetimes.
Transient services are created every time they are requested, suitable for lightweight stateless helpers. Scoped services are created once per HTTP request and shared within it; DbContext is registered as scoped. Singleton services are created once for the whole application lifetime, suitable for caches and configuration. Choose based on state: anything holding per-request data must not be singleton, and singletons must be thread-safe.
22
What is ASP.NET Core and what are its main features?
ASP.NET Core is the open-source, cross-platform framework for building web APIs, MVC sites, Razor Pages, Blazor apps and real-time apps with SignalR on modern .NET. Key features are built-in dependency injection, a configurable middleware pipeline, the fast Kestrel web server, unified configuration and logging, and support for Docker and cloud hosting. It runs on Windows, Linux and macOS and consistently ranks among the fastest web frameworks.
23
When would you choose an array, a List<T> or a LinkedList<T>?
An array has a fixed size and fastest index access, good when the count is known. List<T> wraps a resizable array, with O(1) index access and amortised O(1) add at the end, and is the default choice for most code. LinkedList<T> gives O(1) insert and remove at a known node but O(n) access by index and poor cache locality, so it is rarely the better option in practice.
24
What is the difference between Select and SelectMany?
Select projects each element to one result, so a list of customers mapped to their orders gives a list of lists. SelectMany projects each element to a sequence and flattens all sequences into one, so customers.SelectMany(c => c.Orders) gives a single list of all orders. In EF Core, SelectMany over a navigation collection translates to a SQL join, which is handy for reports.
25
What is the difference between compile-time and runtime polymorphism?
Compile-time, or static, polymorphism is resolved by the compiler, mainly through method overloading and operator overloading, and through generics. Runtime, or dynamic, polymorphism is resolved when the program runs, through virtual methods and interfaces: a Shape reference may call Circle.Area or Square.Area depending on the actual object. Runtime polymorphism is what makes plugin designs and dependency injection possible.
26
How do model binding and validation work in ASP.NET Core Web API?
Model binding maps request data into action parameters from the route, query string, headers or body, using [FromRoute], [FromQuery] and [FromBody]. Validation uses data annotations like [Required], [StringLength] and [Range] on DTOs. With [ApiController], invalid models automatically return 400 Bad Request with ProblemDetails listing the errors, so you do not need to check ModelState manually. FluentValidation is popular for complex rules.
27
Write a LINQ query that joins orders with customers and returns customer name and order total.
var result = orders
.Join(customers,
o => o.CustomerId,
c => c.Id,
(o, c) => new { c.Name, o.Total })
.ToList();
// query syntax
var result2 = (from o in orders
join c in customers on o.CustomerId equals c.Id
select new { c.Name, o.Total }).ToList();
Join is an inner join. For a left join use GroupJoin with DefaultIfEmpty, or the LeftJoin operator added in .NET 10.
28
How are exceptions handled in async code, and what is AggregateException?
When you await a faulted task, the original exception is rethrown, so normal try-catch works. If you block with .Wait() or .Result, the exception is wrapped in AggregateException. With Task.WhenAll, await throws only the first exception, but the returned task's Exception property holds all of them in an AggregateException. Unobserved exceptions from fire-and-forget tasks are silently lost, so always await or log them.
29
What are the four pillars of object-oriented programming?
Encapsulation hides internal state behind methods and properties. Abstraction exposes only what the caller needs, using abstract classes and interfaces. Inheritance lets a class reuse and extend another class. Polymorphism lets one interface have many implementations, so code calls Pay() without knowing whether it is a card or UPI payment. Together they make code easier to change, test and reuse.
30
Show bulk update and delete with ExecuteUpdate and ExecuteDelete.
// mark all unpaid invoices older than 30 days as overdue
int updated = await db.Invoices
.Where(i => !i.IsPaid && i.DueDate < DateTime.UtcNow.AddDays(-30))
.ExecuteUpdateAsync(s => s
.SetProperty(i => i.Status, "Overdue")
.SetProperty(i => i.UpdatedAt, DateTime.UtcNow));
// delete old logs
int deleted = await db.AuditLogs
.Where(l => l.CreatedAt < cutoff)
.ExecuteDeleteAsync();
These run a single SQL UPDATE or DELETE without loading entities, available since EF Core 7. They bypass the change tracker.
Tips to crack the Persistent Systems .NET Full Stack interview
Practise coding problems of easy to medium difficulty, as Persistent assessments usually focus more on programming than service peers.
Revise data structures, OOP, DBMS and operating system basics for the technical rounds.
Read about Persistent's product engineering background and its partnerships with major cloud providers.
Keep a one-minute story ready for every project on your CV: problem, your part, tools, result.
Practise the hard questions on this page aloud; Persistent Systems interviewers usually ask follow-ups on your first answer.
Frequently asked questions
How many rounds are there in the Persistent Systems .NET Full Stack interview?
Candidates usually go through 4 stages: Online assessment (aptitude + coding); Technical round 1; Technical round 2; HR round. The exact rounds change with the role, team, location and your experience, so confirm the process with the recruiter.
Which topics should I prepare for the Persistent Systems .NET Full Stack interview?
This practice set leans on SQL Server and T-SQL (5), Angular and React Front End (4), LINQ, Collections and Generics (4), Async Programming and Multithreading (4). Revise those first, then practise explaining one or two of your own projects end to end, because most Persistent Systems interviewers ask you to walk through real work.
Are these the exact questions asked at Persistent Systems?
No. These are curated practice questions that match the skills and difficulty usually tested in it services interviews like Persistent Systems's. They are not a leaked or verified list of past questions.
Where does Persistent Systems hire .NET Full Stack professionals in India?
Persistent Systems has large teams in Pune, Nagpur, Bengaluru, Hyderabad, Goa. Openings and locations change often, so check the Persistent Systems careers page and filter by city and experience.