Logical Checks

Sometimes you don't need the data; you just need to know if the data Exists or if it Complies with a rule.

1. Any: Existence Check

Checks if a sequence contains ANY elements. **Architect Tip:** Always prefer .Any() over .Count() > 0. Any() returns true as soon as it finds the first match (Short-circuiting), whereas Count() must enumerate the entire list to find the total before comparing.

2. All: Complete Compliance

Returns true ONLY if every single element in the sequence matches the predicate. This is excellent for validation logic (e.g., 'Ensure all line items have a positive price').

3. Contains: Value Matching

Checks if a specific object or value exists in the sequence. For objects, this uses Equality Comparers. **Tip:** In EF Core, list.Contains(id) is translated into a SQL IN (...) clause, which is highly efficient for bulk lookups.

3. Architect Insight

Q: "Should I check for null before using Any()?"

Architect Answer: "Yes. LINQ methods are extension methods, but they will still throw a NullReferenceException if the source collection itself is null. Use the null-conditional operator: myList?.Any() == true to safely check without crashing."