profile for Cullen Tsering at Stack Overflow, Q&A for professional and enthusiast programmers

Sunday, May 4, 2014

An architectural decision and a simple custom sorting

Context:

Recently, I worked on a requirement that required a list of job schedules to be sorted according to priorities imposed on the value of a property of the job schedule, on a ASP.NET MVC view of a web app.  I can put the logic that sorts the data anywhere in the stack to meet this particular requirement.  I could put the sorting logic in the SQL query, or in the repository method after getting the data, or I can sort the data at the controller level before feeding to it to the view that renders it.   The SQL query and the repository method are used by other code that doesn’t need the data sorted so I’d be adding undue burden to other code when the data doesn’t need to be sorted.  I decided to sort the data at the controller level.  This is a trieval design decision but I think this thought process is important to ensure the scalability of your application architecture.

The Requirement:

Given the schedule priority with the following values:
“A” : AM
“P” : PM
“O” : Any time
“F”  : First

the schedule list should be sorted in the following order:
  1. “F”  : First
  2. “A” : AM
  3. “O” : Any time
  4. “P” : PM

As you can see from the data I cannot sort the list using the values’ alphabetical order.  That means I need to create a custom comparer to be used to the value in this manner.

The Code:

Here is the job schedule class:
public class JobSchedule
{
public string Customer { get; set; }
public string SchedulePriority { get; set; }
public override string ToString()
{
    return string.Format("{0} :: {1}", Customer, SchedulePriority);
}
}
The priority class:
public class SchedulePriority
{
public SchedulePriority(string code, string description)
{
    Code = code;
    Description = description;
}
public string Code { get; private set; }
public string Description { get; private set; }
public override string ToString()
{
    return string.Format("{0} :: {1}", Code, Description);
}
}
Below is a sample list data:
var list = new List<JobSchedule>{
new JobSchedule{
    Customer = "jon",
       SchedulePriority = new SchedulePriority("P","PM")
},
new JobSchedule{
    Customer = "jane",
       SchedulePriority = new SchedulePriority("O","Any")
},
new JobSchedule{
    Customer = "bob",
       SchedulePriority = new SchedulePriority("A","AM")
},
new JobSchedule{
    Customer = "bonnie",
       SchedulePriority = new SchedulePriority("F","First")
},
};
The requirement is to sort is this order:
“F”, “A”, “O”, “P”
If I were to sort it alphabetically as the following:
    Console.WriteLine("Sort by Alphabetical Order and the result does NOT match the requirement");
    foreach (var js in list.OrderBy(m => m.SchedulePriority.Code))
    {
        Console.WriteLine(js.ToString());
    }
This is the result I get:
Sort by Alphabetical Order and the result does not meet the requirement
bob :: A :: AM
bonnie :: F :: First
jane :: O :: Any
jon :: P :: PM
So we create a custom comparer by implementing the ICompare interface:
public class SchedulePriorityOrderComparer : IComparer<SchedulePriority>
{
readonly Dictionary<string, int> _priorities = new Dictionary<string, int>() {
    {"F", 1},
    {"A", 2},
    {"O", 3},
    {"P", 4}
};
public int Compare(SchedulePriority x, SchedulePriority y)
{
    if (string.IsNullOrWhiteSpace(x.Code) || string.IsNullOrWhiteSpace(y.Code)) return 0;
    return _priorities[x.Code] - _priorities[y.Code];
}
}
Now I can sort it this as follows:
Console.WriteLine("Sort by Alphabetical Order and the result MATCH the requirement");
foreach (var js in list.OrderBy(m => m.SchedulePriority, new SchedulePriorityOrderComparer()))
{
        Console.WriteLine(js.ToString());
}
And the result now looks like this:
Sort by custom order and the result MATCH the requirement
bonnie :: F :: First
bob :: A :: AM
jane :: O :: Any
jon :: P :: PM

Full code list:

A sample cosole app has been created as a gist here on GitHub  to demo the approach.

About Cullen

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Christian, Father, Software Developer/Architect who enjoys technology and using it to make people's lives easier!

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