LINQ Interview Question #25

Why is it important to know whether a LINQ query is executed in memory or by a database provider?

LINQ Fundamentals, Syntax, IEnumerable & IQueryable Junior Beginner

Quick Interview Answer

The execution location affects performance, supported operations, memory usage, network traffic, and even query semantics. An IEnumerable<T> query normally runs in application code, while an IQueryable<T> query may be translated and executed by a remote provider such as a database.

Detailed Explanation

For database work, filtering, projection, ordering, and pagination should usually remain provider-translatable until the necessary data has been retrieved. Materializing too early can cause unnecessary rows and columns to be loaded into memory.

Code Example

// Better: filter before materialization.
var products = await db.Products
    .Where(p => p.IsActive && p.Price > 100)
    .Select(p => new { p.Id, p.Name })
    .ToListAsync();

// Avoid loading the whole table before filtering
// unless in-memory processing is intentional.