LINQ: let Clause

In this post, let's see what let is in LINQ query-syntax queries. I think it's an overlooked feature in LINQ.

Let's consider the following query.

IQueryable<string> wfhEmployees = from e in context.Employees
                                  where context.Departments
                                      .Where(d => d.IsWfhAllowed)
                                      .Select(d => d.Id)
                                      .Contains(e.DepartmentId)
                                  select e.FirstName + " " + e.LastName;

Here some might find it hard to understand the where condition immediately, we can use the let clause to make it more readable.

IQueryable<string> wfhEmployees = from e in context.Employees
                                  let wfhDepartments = context.Departments
                                      .Where(d => d.IsWfhAllowed)
                                      .Select(d => d.Id)
                                      .ToList()
                                  where wfhDepartments
                                      .Contains(e.DepartmentId)
                                  let fullName = e.FirstName + " " + e.LastName
                                  select fullName;

Here I have used let to store the result of a subexpression to use it in subsequent clauses. This is really handy when you have complex queries, we can break it into multiple sub-expressions.

Hope this helps!

Happy Coding.

Regards,

Jaliya