All 18 LINQ questions
More in LINQ
What is LINQ and what is deferred execution? What is LINQ, and what are the two main syntax styles you can use to write a LINQ query? What is the difference between Where() and Select() in a LINQ query? What is the difference between First, FirstOrDefault and Single? What is the difference between Select and SelectMany? What is 'deferred execution' in LINQ, and how does it differ from calling .ToList() or .ToArray() immediately? How do GroupBy() and its resulting IGrouping<TKey, TElement> work? What is the difference between First(), FirstOrDefault(), Single(), and SingleOrDefault()? What is LINQ, and how does it simplify querying collections compared to writing manual loops? What is the difference between IEnumerable<T>, IQueryable<T>, and List<T>, and how does choosing the wrong one hurt performance against a database?
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C# › LINQ

What is the difference between IEnumerable and IQueryable in LINQ?

Intermediate

Answer

IEnumerable executes in memory (LINQ-to-Objects); IQueryable builds an expression tree a provider (EF Core) translates to SQL, so filtering happens in the database.
IQueryable<User> q = db.Users.Where(u => u.Active); // -> SQL WHERE
IEnumerable<User> m = list.Where(u => u.Active);     // in memory
Real-world example Calling Where before ToList on a DbSet pushes the filter to the database instead of loading every row.
All 18 LINQ questions