Design Pattern to output separate different files from same input parameter

Question

I have this Food class with 20 properties. I need to use this Food class and output 3 different files, using variations of these 20 fields. For example, File 1 contains output only 8 fields. File 2 contains 15 fields. File 3 contains 18 fields.

So right now, I have these 3 separate methods.

    FoodService()
    {
        void WriteRecommendedFood(IList<Food> foodList);
        void WriteRecommendedFoodCalculation(IList<Food> foodList);
        void WriteRecommendedFoodAllEligibleFoods(IList<Food> foodList);
    }

So I'd write:

    public void WriteRecommendedFood(IList<Food> foodList)
    {
            using (StreamWriter sw = new StreamWriter("file.csv", false)
            {
                    StringBuilder sb = new StringBuilder();
                    foreach (Food f in foodList)
                    {
                            sb.Append(f.Field1); 
                            //Repeat for the # of fields I want to spit out
                            sb.Clear();
                            sw.WriteLIne(sb.ToString());
                    }
                    sw.Close();
            }
    }

I feel like I'm writing the same code three times (with slight variations). I started to read up on different design patterns like Visitor and Strategy pattern, but I'm not sure which design pattern to improve my code. (Note: I only need to output it to a comma delimited file at this time. Also, from the UI side, the user gets to select which one they want to output (either one to all 3 files.) Any suggestions?

Jon · Accepted Answer · 2014-09-02 22:33:16Z

2

It seems that the only thing that changes between these three functions is a list of fields that get written. There are several ways you can represent "a field" (and thus a list of fields) in a program; one of the most convenient is doing so as a function that extracts this field's value from a Food instance.

The type of this representation would be Func<Food, object>, so with a List<Func<Food, object>> you are good to go.

public void WriteFoodData(IEnumerable<Food> foodList, IEnumerable<Func<Food, object>> valueProviders)
{
    using (StreamWriter sw = new StreamWriter("file.csv", false))
    {
        StringBuilder sb = new StringBuilder();
        foreach (Food f in foodList)
        {
            foreach (var provider in valueProviders)
            {
                sb.Append(provider(f).ToString());
            }
            sw.WriteLIne(sb.ToString());
            sb.Clear();
        }
    }
}

Now you can create a "list of fields" and use it to call this method:

var valueProviders = new List<Func<Food, object>>
{
    f => f.Field1,
    f => f.Field4,
    // etc
};

var foods = /* whatever */
WriteFoodData(foods, valueProviders);

answered Sep 2, 2014 at 22:33

Jon

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1 Comment

minerva Over a year ago

Thank you Jon! I appreciate your feedback and example!

venerik · Accepted Answer · 2014-09-02 22:43:24Z

1

I would remove the responsibility for formatting from your FoodService and inject it instead.

    public class FoodService()
    {
        public void WriteRecommendedFood(IList<Food> foodList, IFoodFormatter formatter)
        {
            using (StreamWriter sw = new StreamWriter("file.csv", false)
            {
                StringBuilder sb = new StringBuilder();
                foreach (Food f in foodList)
                {
                   sw.WriteLine(foodformatter.Format(f));
                }
                sw.Close();
            }
        }
    }

    interface IFoodFormatter
    {
        string Format(Food f);
    }

This whay you can create concrete formatters like CalculationFormatter and ElligableFoodsFormatter.

answered Sep 2, 2014 at 22:43

venerik

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2 Comments

minerva Over a year ago

Thanks venerik! I like this idea too.

minerva Over a year ago

I ended up using this design since it was more readable to others. In addition, I also was able to modify the format of each item (especially handling some fields contains commas). Thanks again!

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