Question

I would like to be able to refactor out the OrderBy clause in a linq expression.

Here is an example of a refactor of the where clause

before:

results = ctx.ActiveUsers     .Where(u => u.CompanyID != 1 &&            (u.LastName.ToLower().Contains(searchString)            || u.Email.ToLower().Contains(searchString)            || u.Company.Name.ToLower().Contains(searchString)))     .OrderBy(u =>  u.LastName ).ThenBy(u => u.FirstName)     .Select(u => new Employee {       ID = u.ID       , FirstName = u.FirstName       , LastName = u.LastName       , Email = u.Email       , CompanyName = u.Company.Name       , CompanyID = u.CompanyID.ToString() }); 

---

after:

results = ctx.ActiveUsers     .Where(Employee.GetExpression(searchString))     .OrderBy(u =>  u.LastName ).ThenBy(u => u.FirstName)     .Select(u => new Employee {       ID = u.ID       , FirstName = u.FirstName       , LastName = u.LastName       , Email = u.Email       , CompanyName = u.Company.Name       , CompanyID = u.CompanyID.ToString() }); 

---

private static Expression<Func<User, bool>> GetExpression(string searchString) {      Expression<Func<User, bool>> p = (u => u.CompanyID != 1 &&                        (u.LastName.ToLower().Contains(searchString)                        || u.Email.ToLower().Contains(searchString)                        || u.Company.Name.ToLower().Contains(searchString)));     return p; } 

I was wondering if the same type of thing would be possible except I would like to refactor the Orderby expression.

Thank you in advance

Answer 1

Assuming you want to actually take a string such as ‘LastName’, ‘FirstName’ etc, I’d do something like:

var unordered = ctx.ActiveUsers                    .Where(Employee.GetExpression(searchString))                    .OrderBy(ordering)                    .Select(u => new Employee {                        ID = u.ID,                        FirstName = u.FirstName,                        LastName = u.LastName,                        Email = u.Email,                        CompanyName = u.Company.Name,                        CompanyID = u.CompanyID.ToString() }); 

and add a new OrderBy extension method:

public static class UserQueryableExtensions {     public static IOrderedQueryable<User> OrderBy(this IQueryable<User> source,                                                   string ordering)     {         switch (ordering)         {             case 'LastName':                 return source.OrderBy(x => x.LastName);             case 'FirstName':                 return source.OrderBy(x => x.FirstName);             case 'Email':                 return source.OrderBy(x => x.Email);             case 'Company':                 return source.OrderBy(x => x.Company);             default:                 throw new ArgumentException('Unknown ordering');         }     } } 

You certainly could do this using reflection, but unless you have a significant set of properties (or you want to use the same routine for different entity types) a switch statement is easier.