Question

I’m trying to cast a List of Dictionary objects to a dataset. The List comes from a JSON parser. I decided to use this as an opportunity to learn about extension methods.

The extension method for a single dictionary works, but the method for a List of Dictionaries doesn’t “look” right to me, mainly because the call becomes

DataSet myExampleDataSet = myExampleDictionary.ToDataSet<Dictionary<string,string>,string,string>();

Am I missing something? Does it really have to be this complicated? Should I just throw the Dictionary .ToDataSet method in a foreach?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Collections;

//fixed code below
namespace TT.Utils
{
    public static class DictionaryExtensions
    {
        /// <summary>
        /// Dictionary to DataSet
        /// </summary>
        /// <typeparam name="TKey"></typeparam>
        /// <typeparam name="TValue"></typeparam>
        /// <param name="currentDictionary"></param>
        /// <returns></returns>
        public static DataSet ToDataSet<TKey, TValue>(this IDictionary<TKey, TValue> currentDictionary)
        {
            DataSet exportedDataSet = new DataSet();
            DataTable exportedDataTable = exportedDataSet.Tables.Add();
            foreach (TKey key in currentDictionary.Keys)
            {
                exportedDataTable.Columns.Add(key.ToString());
            }
            DataRow newRow = exportedDataTable.NewRow();
            foreach (KeyValuePair<TKey, TValue> entry in currentDictionary)
            {
                string key = entry.Key.ToString();

                string val = string.Empty;
                if (entry.Value != null)
                {
                    val = entry.Value.ToString();
                }

                newRow[key] = val;

            }
            exportedDataSet.Tables[0].Rows.Add(newRow);
            return exportedDataSet;
        }

        /// <summary>
        /// List of dictionaries to dataset
        /// </summary>
        /// <typeparam name="TKey"></typeparam>
        /// <typeparam name="TValue"></typeparam>
        /// <param name="currentList"></param>
        /// <returns></returns>
        public static DataSet ToDataSet<TKey,TValue>(this IList<Dictionary<TKey,TValue> currentList)
        {
            DataSet exportedDataSet = new DataSet();
            DataTable exportedDataTable = exportedDataSet.Tables.Add();



            foreach (Dictionary<TKey, TValue> currentDictionary in currentList.Cast<Dictionary<TKey,TValue>>())
            {
                foreach (TKey key in currentDictionary.Keys)
                {
                    if (!exportedDataTable.Columns.Contains(key.ToString()))
                        exportedDataTable.Columns.Add(key.ToString());
                }
                DataRow newRow = exportedDataTable.NewRow();
                foreach (KeyValuePair<TKey, TValue> entry in currentDictionary)
                {
                    string key = entry.Key.ToString();

                    string val = string.Empty;
                    if (entry.Value != null)
                    {
                        val = entry.Value.ToString();
                    }

                    newRow[key] = val;

                }
                exportedDataSet.Tables[0].Rows.Add(newRow);
            }

            return exportedDataSet;
        }



    }
}

Answer 1

You generally don’t need to explicitly define the generic type arguments used when calling a generic method. The types will be implied by the types of the arguments you are calling with. If there’s an ambiguity, the compiler will let you know.

e.g.,

IDictionary<string, string> myExampleDictionary = ...;
DataSet myExampleDataSet = myExampleDictionary.ToDataSet();
// equivalent to:          myExampleDictionary.ToDataSet<string, string>();

IDictionary<string, int> anotherDictionary = ...;
DataSet anotherDataSet = anotherDictionary.ToDataSet();
// equivalent to:        anotherDictionary.ToDataSet<string, int>();

Oops, I didn’t realize you overloaded ToDataSet(). I only saw the first one which took a single IDictionary<TKey, TValue>.

But either way, the second overload should have the generic parameters the same as the first. It will be a IList of IDictionarys so it should be in this form:

public static DataSet ToDataSet<TKey, TValue>(this IList<IDictionary<TKey, TValue>> currentList)
{
    // ...
}

There are only 2 unknown types here, TKey and TValue and that will be implied as usual.

IList<IDictionary<string, string>> myList = ...;
DataSet myDataSet = myList.ToDataSet();
// equivalent to:   myList.ToDataSet<string, string>();

IDictionary<string, int> anotherList = ...;
DataSet anotherDataSet = anotherList.ToDataSet();
// equivalent to:        anotherList.ToDataSet<string, int>();