Rule Definition
Calling .ToList() or .ToArray() materializes the query immediately, executing it and loading all results into memory. Applying additional LINQ operators after that (e.g., .Where(), .Select(), .OrderBy()) causes: Unnecessary memory usage Loss of deferred execution and query optimization Performance bottlenecks with large datasets Instead, you should: Defer execution using .AsEnumerable() if you need to switch from LINQ to Entities to LINQ to Objects Avoid materialization until absolutely necessary (e.g., at the end of the query chain)

Remediation
Apply further filtering/sorting operations before calling .ToList() or .ToArray(). Use .AsEnumerable() only when switching to in-memory LINQ processing is intentional.

Violation Code Sample

using System.Linq;

// ...

var data = dbContext.Users.ToList()       // ⚠️ VIOLATION: query executes here
               .Where(u => u.IsActive)
               .OrderBy(u => u.Name);

// This loads all users into memory before filtering and sorting — a waste of resources if the dataset is large

Fixed Code Sample

using System.Linq;

// ...

// Execute filters in SQL before materializing
var data = dbContext.Users
               .Where(u => u.IsActive)
               .OrderBy(u => u.Name)
               .ToList();                 // ✓ FIXED: materialize after filtering/sorting


// If switching to LINQ-to-Objects explicitly

var data = dbContext.Users
               .Where(u => u.IsActive)
               .AsEnumerable()            // ✓ FIXED : switch to in-memory for complex logic
               .Where(u => SomeCustomFilter(u));

https://learn.microsoft.com/en-us/dotnet/framework/data/adonet/ef/language-reference/queryable-and-enumerable-operators https://learn.microsoft.com/en-us/ef/core/performance/query-performance#avoid-premature-query-execution https://learn.microsoft.com/en-us/dotnet/fundamentals/code-analysis/quality-rules/ca1862 Microsft Entity Framework - Efficient Querying - Buffering and streaming https://learn.microsoft.com/en-us/ef/core/performance/efficient-querying#buffering-and-streaming LINQ Stinks - code smells in your LINQ - LINQ Stink #2 - Reading too much https://www.markheath.net/post/linq-stinks Enhancing Database Query Performance with Entity Framework Core: Real-world Examples and Performance Metrics Example 3: Query Projection for Minimizing Data Transfer https://mohamed-hendawy.medium.com/enhancing-database-query-performance-with-entity-framework-core-real-world-examples-and-3899f285e67c