Interview Q&A

Short answer: How to calculate running totals using LINQ? var salaries = employees.Select(e => e.Salary).ToList(); double runningTotal = 0; var runningTotals = salaries.Select(s => runningTotal += s); foreach (var total in runningTotals) Console.WriteLine(total); Explanation: Accumulates sums as you iterate through the sequence.

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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: if (!string.IsNullOrEmpty(searchName)) { } Explanation: Build LINQ queries dynamically based on conditions. string searchName = "Alice"; var query = employees.AsQueryable(); query = query.Where(e => e.Name.Contains(searchName)); var result = query.ToList();

Example code

if (!string.IsNullOrEmpty(searchName)) { } Explanation: Build LINQ queries dynamically based on conditions. string searchName = "Alice";
var query = employees.AsQueryable();
query = query.Where(e => e.Name.Contains(searchName));
var result = query.ToList();

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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 perform conditional LINQ queries? string searchName = "Alice"; var query = employees.AsQueryable(); if (!string.IsNullOrEmpty(searchName)) query = query.Where(e => e.Name.Contains(searchName)); var result = query.ToList(); Follow : Explanation: Build LINQ queries dynamically based on conditions. How to perform conditional LINQ queries? string…… searchName = "Alice"; var query = employees.AsQueryable(); if…

Explain a bit more

(!string.IsNullOrEmpty(searchName)) query = query.Where(e => e.Name.Contains(searchName)); var result = query.ToList(); Follow : Explanation: Build LINQ queries dynamically based on conditions.

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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: { new { Department = "IT", Employees = new [] {"Bob", "Charlie"} }, new { Department = "HR", Employees = new [] {"Alice", "Eva"} } }; foreach (var emp in allEmployees) Console.WriteLine(emp); Explanation: SelectMany flattens nested collections into a single sequence. var departmentsWithEmployees = new[]

Example code

var allEmployees = departmentsWithEmployees
.SelectMany(d => d.Employees);

Real-world example (ShopNest)

ShopNest maps entities to DTOs with .Select(o => new OrderSummaryDto { Id = o.Id, Total = o.Total }) so the API does not leak internal fields.

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 flatten hierarchical data with SelectMany?

Explain a bit more

var departmentsWithEmployees = new[] new { Department = "IT", Employees = new [] {"Bob", "Charlie"} new { Department = "HR", Employees = new [] {"Alice", "Eva"} } var allEmployees = departmentsWithEmployees .SelectMany(d => d.Employees); foreach (var emp in allEmployees) Console.WriteLine(emp); Explanation: SelectMany flattens nested collections into a single sequence.

Real-world example (ShopNest)

ShopNest maps entities to DTOs with .Select(o => new OrderSummaryDto { Id = o.Id, Total = o.Total }) so the API does not leak internal fields.

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 groupJoin = from d in departments into empGroup var groupJoin = from d in departments into empGroup var groupJoin = from d in departments into empGroup var groupJoin = from d in departments into empGroup var groupJoin = from d in departments into empGroup var groupJoin = from d in departments into empGroup var groupJoin = from d in departments into empGroup var groupJoin = from d in departments into empGroup

Example code

var groupJoin = from d in departments into empGroup var groupJoin = from d in departments into empGroup var groupJoin = from d in departments into empGroup var groupJoin = from d in departments into empGroup var groupJoin = from d in departments into empGroup var groupJoin = from d in departments into empGroup var groupJoin = from d in departments into empGroup var groupJoin = from d in departments into empGroup

Real-world example (ShopNest)

A sales report joins orders and customers, then GroupBy(c => c.City) to show revenue per city.

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 group join with multiple collections?

Explain a bit more

var groupJoin = from d in departments join e in employees on d.Name equals e.Department into empGroup select new { Department = d.Name, Employees = empGroup }; foreach (var group in groupJoin) Console.WriteLine($"{group.Department}:"); foreach (var emp in group.Employees) Console.WriteLine($" - {emp.Name}"); Follow : Explanation: Groups employees under their respective departments.

Real-world example (ShopNest)

A sales report joins orders and customers, then GroupBy(c => c.City) to show revenue per city.

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: int pageNumber = 2; int pageSize = 2; var page = employees int pageNumber = 2; int pageSize = 2; var page = employees int pageNumber = 2; int pageSize = 2; var page = employees int pageNumber = 2; int pageSize = 2; var page = employees int pageNumber = 2; int pageSize = 2; var page = employees int pageNumber = 2; int pageSize = 2; var page = employees int pageNumber = 2; int pageSize = 2; var page = employees int…

Explain a bit more

pageNumber = 2; int pageSize = 2; var page = employees

Example code

int pageNumber = 2; int pageSize = 2; var page = employees int pageNumber = 2; int pageSize = 2; var page = employees int pageNumber = 2; int pageSize = 2; var page = employees int pageNumber = 2; int pageSize = 2; var page = employees int pageNumber = 2; int pageSize = 2; var page = employees int pageNumber = 2; int pageSize = 2; var page = employees int pageNumber = 2; int pageSize = 2; var page = employees int pageNumber = 2; int pageSize = 2; var page = employees

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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 use LINQ for paging data? int pageNumber = 2; int pageSize = 2; var page = employees .OrderBy(e => e.Id) .Skip((pageNumber - 1) * pageSize) .Take(pageSize); Explanation: Retrieve specific pages from data sets (useful for UI pagination). How to use LINQ for paging data? int pageNumber = 2; int pageSize = 2; var page = employees .OrderBy(e => e.Id)…… Skip((pageNumber - 1) * pageSize) .Take(pageSize);…

Explain a bit more

Explanation: Retrieve specific pages from data sets (useful for UI pagination).

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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 maxSalaryPerDept = employees var maxSalaryPerDept = employees var maxSalaryPerDept = employees var maxSalaryPerDept = employees var maxSalaryPerDept = employees var maxSalaryPerDept = employees var maxSalaryPerDept = employees var maxSalaryPerDept = employees

Example code

var maxSalaryPerDept = employees var maxSalaryPerDept = employees var maxSalaryPerDept = employees var maxSalaryPerDept = employees var maxSalaryPerDept = employees var maxSalaryPerDept = employees var maxSalaryPerDept = employees var maxSalaryPerDept = employees

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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 find max salary per department? var maxSalaryPerDept = employees .GroupBy(e => e.Department) .Select(g => new { Department = g.Key, MaxSalary = g.Max(e => e.Salary) }); How to find max salary per department? var maxSalaryPerDept = employees .GroupBy(e => e.Department) .Select(g => new { Department = g.Key, MaxSalary = g.Max(e => e.Salary) }); How to… find max salary per department? var maxSalaryPerDept =…

Explain a bit more

employees .GroupBy(e => e.Department) .Select(g => new { Department = g.Key, MaxSalary = g.Max(e => e.Salary) }); How to find max salary per department? var maxSalaryPerDept = employees .GroupBy(e => e.Department) .Select(g => new { Department = g.Key, MaxSalary = g.Max(e => e.Salary) });

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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: .SequenceEqual(anotherList.Select(e => e.Id).OrderBy(id => id)); .SequenceEqual(anotherList.Select(e => e.Id).OrderBy(id => id)); .SequenceEqual(anotherList.Select(e => e.Id).OrderBy(id => id)); .SequenceEqual(anotherList.Select(e => e.Id).OrderBy(id => id));

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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 check sequence equality ignoring order?

Explain a bit more

bool areEqual = employees.Select(e => e.Id).OrderBy(id => id) .SequenceEqual(anotherList.Select(e => e.Id).OrderBy(id => id)); How to check sequence equality ignoring order? bool areEqual = employees.Select(e => e.Id).OrderBy(id => id) .SequenceEqual(anotherList.Select(e => e.Id).OrderBy(id => id)); How to check sequence equality ignoring order? bool areEqual = employees.Select(e => e.Id).OrderBy(id => id) .SequenceEqual(anotherList.Select(e => e.Id).OrderBy(id => id)); How to check sequence equality ignoring order? bool areEqual = employees.Select(e => e.Id).OrderBy(id => id) .SequenceEqual(anotherList.Select(e => e.Id).OrderBy(id => id));

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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 distinctByDeptAndSalary = employees .Select(g => g.First()); var distinctByDeptAndSalary = employees .Select(g => g.First()); var distinctByDeptAndSalary = employees .Select(g => g.First()); var distinctByDeptAndSalary = employees .Select(g => g.First()); var distinctByDeptAndSalary = employees .Select(g => g.First()); var distinctByDeptAndSalary = employees .Select(g => g.First()); var distinctByDeptAndSalary =…

Explain a bit more

employees .Select(g => g.First()); var distinctByDeptAndSalary = employees .Select(g => g.First());

Example code

var distinctByDeptAndSalary = employees .Select(g => g.First()); var distinctByDeptAndSalary = employees .Select(g => g.First()); var distinctByDeptAndSalary = employees .Select(g => g.First()); var distinctByDeptAndSalary = employees .Select(g => g.First()); var distinctByDeptAndSalary = employees .Select(g => g.First()); var distinctByDeptAndSalary = employees .Select(g => g.First()); var distinctByDeptAndSalary = employees .Select(g => g.First()); var distinctByDeptAndSalary = employees .Select(g => g.First());

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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 get distinct by multiple properties?

Explain a bit more

var distinctByDeptAndSalary = employees .GroupBy(e => new { e.Department, e.Salary }) .Select(g => g.First()); How to get distinct by multiple properties? var distinctByDeptAndSalary = employees .GroupBy(e => new { e.Department, e.Salary }) .Select(g => g.First()); How to get distinct by multiple properties? var distinctByDeptAndSalary = employees .GroupBy(e => new { e.Department, e.Salary }) .Select(g => g.First()); How to get distinct by multiple properties? var distinctByDeptAndSalary = employees .GroupBy(e => new { e.Department, e.Salary }) .Select(g => g.First());

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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: .OrderBy(e => e.Id) .Skip((pageNumber - 1) * pageSize) .Take(pageSize) .ToList(); Console.WriteLine($"Total Employees: {totalCount}"); foreach(var emp in pageData) Console.WriteLine($"{emp.Name} - {emp.Department}"); Explanation: You get total count separately and then take the required page using Skip and Take. int pageNumber = 1;

Example code

int pageSize = 3;
var totalCount = employees.Count();
var pageData = employees

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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 implement pagination with total count using LINQ?

Explain a bit more

int pageNumber = 1; Follow : int pageSize = 3; var totalCount = employees.Count(); var pageData = employees .OrderBy(e => e.Id) .Skip((pageNumber - 1) * pageSize) .Take(pageSize) .ToList(); Console.WriteLine($"Total Employees: {totalCount}"); foreach(var emp in pageData) Console.WriteLine($"{emp.Name} - {emp.Department}"); Explanation: You get total count separately and then take the required page using Skip and Take.

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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 list1 = new[] {1, 2, 3, 4}; var list2 = new[] {4, 3, 2, 1}; var list1 = new[] {1, 2, 3, 4}; var list2 = new[] {4, 3, 2, 1}; var list1 = new[] {1, 2, 3, 4}; var list2 = new[] {4, 3, 2, 1}; var list1 = new[] {1, 2, 3, 4}; var list2 = new[] {4, 3, 2, 1}; var list1 = new[] {1, 2, 3, 4}; var list2 = new[] {4, 3, 2, 1}; var list1 = new[] {1, 2, 3, 4}; var list2 = new[] {4, 3, 2, 1}; var list1 = new[] {1, 2, 3, 4}; var…

Explain a bit more

list2 = new[] {4, 3, 2, 1}; var list1 = new[] {1, 2, 3, 4}; var list2 = new[] {4, 3, 2, 1};

Example code

var list1 = new[] {1, 2, 3, 4}; var list2 = new[] {4, 3, 2, 1}; var list1 = new[] {1, 2, 3, 4}; var list2 = new[] {4, 3, 2, 1}; var list1 = new[] {1, 2, 3, 4}; var list2 = new[] {4, 3, 2, 1}; var list1 = new[] {1, 2, 3, 4}; var list2 = new[] {4, 3, 2, 1}; var list1 = new[] {1, 2, 3, 4}; var list2 = new[] {4, 3, 2, 1}; var list1 = new[] {1, 2, 3, 4}; var list2 = new[] {4, 3, 2, 1}; var list1 = new[] {1, 2, 3, 4}; var list2 = new[] {4, 3, 2, 1}; var list1 = new[] {1, 2, 3, 4}; var list2 = new[] {4, 3, 2, 1};

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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 check if two sequences have the same elements regardless of order and duplicates? var list1 = new[] {1, 2, 3, 4}; var list2 = new[] {4, 3, 2, 1}; bool areEqual = !list1.Except(list2).Any() && !list2.Except(list1).Any(); Console.WriteLine(areEqual); // Output: True Explanation: This checks if both lists contain the same elements, ignoring order and duplicates.

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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 dict = employees .ToDictionary(g => g.Key, g => g.ToList()); var dict = employees .ToDictionary(g => g.Key, g => g.ToList()); var dict = employees .ToDictionary(g => g.Key, g => g.ToList()); var dict = employees .ToDictionary(g => g.Key, g => g.ToList()); var dict = employees .ToDictionary(g => g.Key, g => g.ToList()); var dict = employees .ToDictionary(g => g.Key, g => g.ToList()); var dict = employees…

Explain a bit more

ToDictionary(g => g.Key, g => g.ToList()); var dict = employees .ToDictionary(g => g.Key, g => g.ToList());

Example code

var dict = employees .ToDictionary(g => g.Key, g => g.ToList()); var dict = employees .ToDictionary(g => g.Key, g => g.ToList()); var dict = employees .ToDictionary(g => g.Key, g => g.ToList()); var dict = employees .ToDictionary(g => g.Key, g => g.ToList()); var dict = employees .ToDictionary(g => g.Key, g => g.ToList()); var dict = employees .ToDictionary(g => g.Key, g => g.ToList()); var dict = employees .ToDictionary(g => g.Key, g => g.ToList()); var dict = employees .ToDictionary(g => g.Key, g => g.ToList());

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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 create a dictionary from a list with duplicate keys? var dict = employees .GroupBy(e => e.Department) .ToDictionary(g => g.Key, g => g.ToList()); Follow : foreach (var kvp in dict) Console.WriteLine($"{kvp.Key} Department:"); foreach (var emp in kvp.Value) Console.WriteLine($" - {emp.Name}"); Explanation: Group employees by department and convert groups to dictionary entries.

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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: foreach (var name in union) Console.WriteLine(name); Explanation: Union returns distinct elements from both collections. var list1 = new[] { "Alice", "Bob", "Charlie" }; var list2 = new[] { "Bob", "David", "Eva" }; var union = list1.Union(list2);

Example code

foreach (var name in union) Console.WriteLine(name); Explanation: Union returns distinct elements from both collections. var list1 = new[] { "Alice", "Bob", "Charlie" };
var list2 = new[] { "Bob", "David", "Eva" };
var union = list1.Union(list2);

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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 perform union of two collections without duplicates? var list1 = new[] { "Alice", "Bob", "Charlie" }; var list2 = new[] { "Bob", "David", "Eva" }; var union = list1.Union(list2); foreach (var name in union) Console.WriteLine(name); Explanation: Union returns distinct elements from both collections.

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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 intersect = list1.Intersect(list2); var intersect = list1.Intersect(list2); var intersect = list1.Intersect(list2); var intersect = list1.Intersect(list2); var intersect = list1.Intersect(list2); var intersect = list1.Intersect(list2); var intersect = list1.Intersect(list2); var intersect = list1.Intersect(list2);

Example code

var intersect = list1.Intersect(list2); var intersect = list1.Intersect(list2); var intersect = list1.Intersect(list2); var intersect = list1.Intersect(list2); var intersect = list1.Intersect(list2); var intersect = list1.Intersect(list2); var intersect = list1.Intersect(list2); var intersect = list1.Intersect(list2);

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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 perform intersection of two collections?

Explain a bit more

var intersect = list1.Intersect(list2); foreach (var name in intersect) Console.WriteLine(name); // Output: Bob How to perform intersection of two collections? var intersect = list1.Intersect(list2); foreach (var name in intersect) Console.WriteLine(name); // Output: Bob How to perform intersection of two collections? var intersect = list1.Intersect(list2); foreach (var name in intersect) Console.WriteLine(name); // Output: Bob How to perform intersection of two collections? var intersect = list1.Intersect(list2); foreach (var name in intersect) Console.WriteLine(name); // Output: Bob

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

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.