How is caching implemented in Entity Framework Core…

Entity Framework Core (EF Core) has two-level caching:

Context Cache (Identity Resolution): This is the first-level cache. EF Core tracks entities loaded into the current DbContext. If EF Core finds an entity with the same key value in the context's memory during a query, it returns the existing instance instead of querying the database.
- Prevents loading the same data multiple times within a single context.
- Automatically updates in-memory instances when their state changes (add, modify, delete).
- Works by default and does not require special configuration.
Query Cache (Query Caching): This is the second-level cache. EF Core caches execution plans of generated SQL queries. When the same query is executed again, EF Core can reuse the already compiled plan, avoiding re-compilation of SQL.
- Optimizes performance of repeated queries with the same structure (but different parameters).
- Caches not the query result (the data itself), but its execution plan.
- Managed by EF Core's internal mechanisms and not directly accessible for external configuration or clearing.

Example of context cache operation:

// assuming a User with Id == 1 exists in the database
using (var context = new AppDbContext())
{
    // First load - database query
    var user1 = context.Users.FirstOrDefault(u => u.Id == 1);
    Console.WriteLine($"User1 loaded: {user1.Name}");

    // Second load - object is retrieved from the context cache
    var user2 = context.Users.FirstOrDefault(u => u.Id == 1);
    Console.WriteLine($"User2 loaded: {user2.Name}");

    // user1 and user2 are references to the same object in memory
    Console.WriteLine($"Are user1 and user2 the same object reference? {ReferenceEquals(user1, user2)}");
}

It is important to understand that EF Core does not provide built-in application-wide data caching (e.g., for storing frequently used data between requests or users). For such scenarios, external solutions like Redis, IMemoryCache, or other distributed caches are typically used.

How is caching implemented in Entity Framework Core?