Explain the principle of data materialization and what it involves.

Data materialization is the process of transforming data from a deferred or lazy state into concrete objects or collections in memory.

In C#, this often occurs when working with LINQ queries. LINQ queries are usually lazy: they are not executed immediately but only when iteration over the result occurs or when methods that require the full result are called (for example, ToList(), ToArray()).

Materialization means that data from a source (such as a database or collection) is loaded and stored in a specific data structure, allowing direct work with it without re-executing the query.

Example:

var query = dbContext.Users.Where(u => u.IsActive);
// The query has not been executed yet

List<User> activeUsers = query.ToList(); // Here, materialization occurs — data is loaded into the list

Thus, materialization is important for controlling when the query is executed and for managing performance.