25 Advanced LINQ Queries Every .NET Developer Should Know

Are you looking to level up your LINQ skills? While you might be comfortable with basic LINQ operations, there’s a whole world of powerful queries that can make your code more elegant and efficient. In this article, we’ll break down 25 advanced LINQ queries in a way that’s easy to understand, with plenty of real-world examples.

You can also check my other article focused on the Advanced Concepts for JOIN in LINQ. 👇

Advanced LINQ Join Strategies: Optimizing Data Operations in .NET

1. Group-Join: Connecting Related Data

Think of Group-Join as a way to connect two lists where one item in the first list relates to multiple items in the second list — like finding all employees in each department.

// Let's say we have departments and employees
var departments = new List<Department>
{
    new Department { Id = 1, Name = "IT" },
    new Department { Id = 2, Name = "HR" }
};

var employees = new List<Employee>
{
    new Employee { Name = "John", DepartmentId = 1 },
    new Employee { Name = "Jane", DepartmentId = 1 },
    new Employee { Name = "Bob", DepartmentId = 2 }
};

// GroupJoin combines them together
var departmentGroups = departments.GroupJoin(
    employees,
    dept => dept.Id,
    emp => emp.DepartmentId,
    (dept, emps) => new {
        DepartmentName = dept.Name,
        EmployeeCount = emps.Count(),
        Employees = emps.Select(e => e.Name)
    });

// Results:
// IT: 2 employees (John, Jane)
// HR: 1 employee (Bob)

Why is this useful? It’s perfect for scenarios like:

• Showing all departments, even those with no employees
• Creating reports that group data by department
• Building hierarchical data structures

2. Multiple Group-By: Organizing Data in Multiple Ways

Sometimes you need to group data by more than one thing at once. For example, grouping employees by both their department and location: