Question

Anyone want to help make me a better programmer?

I have an application where I am filtering a collection of objects on a variety of criteria. Right now my code works, but 90% is duplicated which I feel like means I am doing something wrong. Any suggestions on how to make more reusable filtering code?

Assuming I have a collection of objects like this:

    public class ExampleData
{
    public int SomeValue1 { get; set; }
    public int SomeValue2 { get; set; }
    public int SomeValue3 { get; set; }
    public string SomeValue4 { get; set; }
}

And here is my filter class. Look at the code comments.

  class ExampleFilter
{
    public ExampleFilter()
    {
    }

    public IEnumerable<ExampleData> applyFilters(SearchCriteria criteria, IEnumerable<ExampleData> data)
    {
        //The body of these methods is almost identical...how can I better design this process so I don't cut and paste 90% of the code?
        data = filterByValue1Selections(criteria.FormTemplateSelected, data);
        data = filterByValue2Selections(criteria.FormTemplateSelected, data);
        return data;
    }

    public IEnumerable<ExampleData> filterByValue1Selections(List<int> value1Ids, IEnumerable<ExampleData> data)
    {
        if (value1Ids != null)
        {
            IEnumerable<ExampleData> dataQuery = null;
            foreach (int selectedValueIds in value1Ids)
            {
                //See http://justgeeks.blogspot.com/2011/01/using-linq-in-foreach-loop-to-build.html
                //For explanation of why we copy this locally
                int selectedId = selectedValueIds;
                if (dataQuery == null)
                {
                    //This code and the similar block in the else are the only differences in these methods
                    dataQuery = data.Where(t => t.SomeValue1 == selectedId);
                }
                else
                {
                    dataQuery = dataQuery.Union(data.Where(t => t.SomeValue1 == selectedId));
                }
            }
            data = dataQuery;
        }
        return data;
    }

    public IEnumerable<ExampleData> filterByValue2Selections(List<int> value2Ids, IEnumerable<ExampleData> data)
    {
        if (value2Ids != null)
        {
            IEnumerable<ExampleData> dataQuery = null;
            foreach (int selectedValueIds in value2Ids)
            {
                //See http://justgeeks.blogspot.com/2011/01/using-linq-in-foreach-loop-to-build.html
                //For explanation of why we copy this locally
                int selectedId = selectedValueIds;
                if (dataQuery == null)
                {
                    dataQuery = data.Where(t => t.SomeValue1 == selectedId);
                }
                else
                {
                    dataQuery = dataQuery.Union(data.Where(t => t.SomeValue1 == selectedId));
                }
            }
            data = dataQuery;
        }
        return data;
    }


}

Answer 1

You are basically re-implementing the Contains() method – you can just do:

List<int> valueIds = ...;
var filteredData = data.Where(x=> valueIds.Contains(x.SomeValue1));

Then your applyFilters method would look like this:

public IEnumerable<ExampleData> applyFilters(SearchCriteria criteria, IEnumerable<ExampleData> data)
{
    data = data.Where(x=> criteria.FormTemplateSelected.Contains(x.SomeValue1)
                       && criteria.FormTemplateSelected.Contains(x.SomeValue2));
    return data;
}