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Kreta.DataAccessManual/Extensions/DataSetExtensions.cs

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+using System;
+using System.Collections.Generic;
+using System.Data;
+using System.Linq;
+
+namespace Kreta.DataAccessManual.Extensions
+{
+    public static class DataSetExtensions
+    {
+        public static List<int> GetIdListFromFirstTable(this DataSet dataSet)
+        {
+            return dataSet.Tables[0]
+                .AsEnumerable()
+                .Select(r => r.Field<int>("ID"))
+                .ToList();
+        }
+
+        public static DataTable ConvertColumnTypes(this DataTable dataTable, Dictionary<string, Type> columnNameColumnTypeDictionary)
+        {
+            var clonedDataTable = dataTable.Clone();
+            foreach (var columnNameColumnType in columnNameColumnTypeDictionary)
+            {
+                clonedDataTable.Columns[columnNameColumnType.Key].DataType = columnNameColumnType.Value;
+            }
+            foreach (DataRow dataRow in dataTable.Rows)
+            {
+                clonedDataTable.ImportRow(dataRow);
+            }
+
+            return clonedDataTable;
+        }
+
+        public static DataTable ConvertColumnType(this DataTable dataTable, string columnName, Type newType)
+        {
+            return dataTable.ConvertColumnTypes(new Dictionary<string, Type> { { columnName, newType } });
+        }
+    }
+}