ASP.NET Linq interview questions

 Basic LINQ Questions

1. What is LINQ in .NET and why is it used in ASP.NET Core applications?

2. Explain the difference between LINQ to Objects, LINQ to SQL, and LINQ to Entities (EF Core).

3. What are deferred execution and immediate execution in LINQ? Give examples.

4. What are query syntax and method syntax in LINQ?

5. What is the difference between Select and SelectMany?

6. What is the difference between Where and FirstOrDefault?

7. Explain the difference between Single, SingleOrDefault, First, and FirstOrDefault.

8. What is the difference between Any() and All()?

9. What is the difference between Count() and LongCount()?

10. How do you perform joins using LINQ (inner join, group join, left join)?

Intermediate LINQ in ASP.NET Core

11. How does LINQ deferred execution impact database queries in EF Core?

12. What is the difference between IQueryable<T> and IEnumerable<T>?

13. What is the use of AsEnumerable(), AsQueryable(), and ToList()?

14. How does GroupBy work in LINQ? Can you group on multiple keys?

15. What is the difference between OrderBy, ThenBy, and ThenByDescending?

16. How do you implement pagination using LINQ (Skip and Take)?

17. What is the difference between Join and GroupJoin?

18. How do you project custom objects using LINQ (select new { })?

19. How do you filter data with complex conditions in LINQ?

20. What is the difference between Distinct, Union, Intersect, and Except?

Advanced LINQ in ASP.NET Core

21. How does LINQ-to-Entities translate queries into SQL in EF Core?

22. What is the impact of using ToList() too early in a LINQ query?

23. How do you handle N+1 query problems in LINQ with EF Core?

24. What is the difference between Include() and ThenInclude() in EF Core LINQ queries?

25. Explain lazy loading vs eager loading vs explicit loading in EF Core LINQ.

26. How does Select projection help improve performance in LINQ queries?

27. What are expression trees in LINQ?

28. What is the difference between IQueryable.Provider and IEnumerable execution?

29. How does LINQ handle deferred execution with closures?

30. How do you debug EF Core LINQ queries to see generated SQL?

Performance & Best Practices

31. How do you optimize LINQ queries in ASP.NET Core EF Core?

32. Why is Any() preferred over Count() > 0 in LINQ?

33. Why should you avoid ToList() in the middle of a query chain?

34. What is the difference between client-side evaluation and server-side evaluation in EF Core LINQ?

35. How do you implement bulk inserts/updates in EF Core without iterating LINQ queries?

36. How do you use AsNoTracking() in EF Core LINQ queries and why?

37. When should you use CompiledQuery in EF Core LINQ?

38. How does deferred execution impact memory usage in ASP.NET Core APIs?

39. What is the difference between synchronous (ToList) and asynchronous (ToListAsync) LINQ queries?

40. How do you handle complex filtering dynamically using LINQ in ASP.NET Core APIs?
    

Additional LINQ Questions (Advanced + Practical)

41. What is the difference between Select and SelectMany with examples?

42. How do you perform a left outer join in LINQ?

43. How do you write a LINQ query to get the second highest salary from a table?

44. What is the difference between Take, TakeWhile, Skip, and SkipWhile?

45. How do you implement paging with sorting using LINQ in EF Core?

46. What is the difference between DefaultIfEmpty and FirstOrDefault?

47. How do you use Aggregate function in LINQ? Give an example.

48. How do you find duplicates in a collection using LINQ?

49. How do you remove duplicates using LINQ (Distinct vs GroupBy)?

50. What is the difference between Concat, Union, Intersect, and Except in LINQ?

51. How do you perform a cross join in LINQ?

52. What is the difference between Max, Min, Average, and Aggregate?

53. How do you get the nth element in a LINQ query safely?

54. How do you combine multiple predicates dynamically in LINQ (like filters in search APIs)?

55. What is the difference between deferred execution and lazy evaluation in LINQ?

56. What is the purpose of the let keyword in LINQ query syntax?

57. How do you execute raw SQL queries with LINQ in EF Core?

58. What is the difference between AsEnumerable() and ToList() in LINQ queries?

59. What is the difference between navigation property loading and Join in LINQ with EF Core?

60. How do you handle NullReferenceException in LINQ queries safely?

61. How does GroupJoin differ from GroupBy?

62. What is the difference between All(), Any(), and Contains() in LINQ?

63. How do you fetch hierarchical data (tree structure) using LINQ?

64. How do you convert LINQ queries into expression trees and compile them?

65. What is the difference between compiled queries in EF Core vs normal LINQ queries?

66. How do you write a LINQ query for dynamic sorting based on column name?

67. How do you write a LINQ query that performs string search with case-insensitivity?

68. How does Include() affect LINQ query performance in EF Core?

69. What is the difference between ThenBy and ThenByDescending?

70. How do you optimize a LINQ query that returns large result sets in ASP.NET Core APIs?