C# - DataTable Examples - Dot Net Perls

DataTable. This class stores rows and columns of data. In C# we can address parts of the DataTable with DataRow and DataColumn. And a DataSet can contain multiple tables.

The DataTable class is part of the System.Data namespace. We add, select and iterate over stored data. The foreach-loop can be used on the Rows in a DataTable.

DataTable Select

DataTable foreach

First example. A key advantage to DataTable is it allows database-like manipulations of data (even simple joins). But before these advanced features can be used, we must create a table.

Step 1 We call GetTable, which generates a table. The returned object could be persisted to disk, displayed, or stored in memory.

Step 2 We create a new DataTable reference. Then we add 4 columns—these include a type, specified with typeof.

typeof

Step 3 We add the actual data as rows. The 4 arguments to each Add() call match up with the 4 columns already added.

Step 4 We print a cell value from the first row (row 0) and the Dosage column (which is an int).

using System; using System.Data; class Program { static void Main() { // Step 1: get the DataTable. DataTable table = GetTable(); // Step 4: print the first cell. Console.WriteLine("FIRST ROW, DOSAGE: {0}", table.Rows[0]["Dosage"]); } static DataTable GetTable() { // Step 2: here we create a DataTable. // ... We add 4 columns, each with a Type. DataTable table = new DataTable(); table.Columns.Add("Dosage", typeof(int)); table.Columns.Add("Drug", typeof(string)); table.Columns.Add("Diagnosis", typeof(string)); table.Columns.Add("Date", typeof(DateTime)); // Step 3: here we add rows. table.Rows.Add(25, "Drug A", "Disease A", DateTime.Now); table.Rows.Add(50, "Drug Z", "Problem Z", DateTime.Now); table.Rows.Add(10, "Drug Q", "Disorder Q", DateTime.Now); table.Rows.Add(21, "Medicine A", "Diagnosis A", DateTime.Now); return table; } }

FIRST ROW, DOSAGE: 25

Rows, field. We build in complexity—here we loop over all Rows of our DataTable. We then access the first field, with the Field extension method, as an int.

Note Field is a generic method. So we must specify its parametric type (here, int) to indicate its behavior.

DataRow Field

Note 2 Often we must access the rows of a DataTable. The Rows property, which can be looped over, is ideal here.

using System; using System.Data; class Program { static void Main() { // This uses the GetTable method (please paste it in). DataTable data = GetTable(); // ... Loop over all rows. foreach (DataRow row in data.Rows) { // ... Write value of first field as integer. Console.WriteLine(row.Field<int>(0)); } } }

25 50 10 21

DataGridView example. We insert data from object collections (like List) into DataTable. We then render that table to the screen with Windows Forms. DataTable helps display data.

Info This code is a Form and can be placed in a Windows Forms application with a DataGridView. It creates a DataTable.

Start The 2 arrays are initialized in the class and constructor. They contain column information.

Next We add the column names to our DataTable with Columns.Add. These are the column headers.

Tip DataTable requires objects to assign to the cells. Objects can hold any type of data.

object

using System.Collections.Generic; using System.Data; using System.Windows.Forms; namespace WindowsFormsApplication1 { public partial class Form1 : Form { /// <summary> /// Contains column names. /// </summary> List<string> _names = new List<string>(); /// <summary> /// Contains column data arrays. /// </summary> List<double[]> _dataArray = new List<double[]>(); public Form1() { InitializeComponent(); // Example column. _names.Add("Cat"); // Three numbers of cat data. _dataArray.Add(new double[] { 1.0, 2.2, 3.4 }); // Another example column. _names.Add("Dog"); // Add three numbers of dog data. _dataArray.Add(new double[] { 3.3, 5.0, 7.0 }); // Render the DataGridView. dataGridView1.DataSource = GetResultsTable(); } /// <summary> /// This method builds a DataTable of the data. /// </summary> public DataTable GetResultsTable() { // Create the output table. DataTable d = new DataTable(); // Loop through all process names. for (int i = 0; i < this._dataArray.Count; i++) { // The current process name. string name = this._names[i]; // Add the program name to our columns. d.Columns.Add(name); // Add all of the memory numbers to an object list. List<object> objectNumbers = new List<object>(); // Put every column's numbers in this List. foreach (double number in this._dataArray[i]) { objectNumbers.Add((object)number); } // Keep adding rows until we have enough. while (d.Rows.Count < objectNumbers.Count) { d.Rows.Add(); } // Add each item to the cells in the column. for (int a = 0; a < objectNumbers.Count; a++) { d.Rows[a][i] = objectNumbers[a]; } } return d; } } }

Using. DataTable can be placed in a using statement. This can help programs performance. Often the using block construct helps improve resource management.

Tip We can add Columns and Rows to the DataTable instance inside (but not outside) the using block.

Tip 2 In this example, the Dispose method is invoked. After the using statement, Dispose() on DataTable is called.

using

Detail When Dispose is called, native resources are released. This may help resource usage problems.

using System; using System.Data; class Program { static void Main() { // Safely create and dispose of a DataTable. using (DataTable table = new DataTable()) { // Two columns. table.Columns.Add("Name", typeof(string)); table.Columns.Add("Date", typeof(DateTime)); // ... Add two rows. table.Rows.Add("cat", DateTime.Now); table.Rows.Add("dog", DateTime.Today); // ... Display first field. Console.WriteLine(table.Rows[0].Field<string>(0)); } } }

cat

Compute. We can use the Compute() method with SUM to sum a column in a DataTable. Here we create a product data table, and add 2 rows to it.

And We call Compute() with a SUM of the column name (like Variety1). The filter argument can be specified as string.Empty.

Result The Total row has the columns summed correctly. We do not need to sum the values with a for-loop.

using System; using System.Data; class Program { static void Main() { var table = new DataTable(); table.Columns.Add("Product", typeof(string)); table.Columns.Add("Variety1", typeof(decimal)); table.Columns.Add("Variety2", typeof(decimal)); table.Columns.Add("Variety3", typeof(decimal)); table.Columns.Add("Variety4", typeof(decimal)); table.Rows.Add("Product 1", 10, 12, 14, 45); table.Rows.Add("Product 2", 20, 15, 24, 0); // Use Compute and SUM to sum up columns. // ... Use string.Empty as the filter as it is not needed. var sum1 = (decimal)table.Compute("SUM(Variety1)", string.Empty); var sum2 = (decimal)table.Compute("SUM(Variety2)", string.Empty); var sum3 = (decimal)table.Compute("SUM(Variety3)", string.Empty); var sum4 = (decimal)table.Compute("SUM(Variety4)", string.Empty); table.Rows.Add("Total", sum1, sum2, sum3, sum4); // Loop over rows. foreach (DataRow row in table.Rows) { Console.WriteLine(":: ROW ::"); foreach (var item in row.ItemArray) { Console.WriteLine(item); } } } }

:: ROW :: Product 1 10 12 14 45 :: ROW :: Product 2 20 15 24 0 :: ROW :: Total 30 27 38 45

Merge, PrimaryKey. We can join 2 DataTables together—each resulting row in the DataTable will contain all data from each table for the key. We must set a PrimaryKey column to use Merge.

Here We create 2 DataTables with names PictureStyle and PictureSize. Each table has a column of IDs, and these IDs match in each table.

Next We assign the PrimaryKey to a column (or array of columns). Here we use the ID column, so we can join on the IDs.

Then We invoke Merge() to join the 2 tables based on their PrimaryKeys. One or more columns can be used.

Result The "PictureStyle" DataTable is updated to include the row fields from the "PictureSize" data table—each row now has 3 cells.

using System; using System.Data; class Program { static void Main() { // Create 1 table, setting ID as PrimaryKey. DataTable tableStyle = new DataTable("PictureStyle"); var idColumn = new DataColumn("ID", typeof(int)); tableStyle.Columns.Add(idColumn); tableStyle.PrimaryKey = new DataColumn[] { idColumn }; tableStyle.Columns.Add(new DataColumn("Style", typeof(string))); tableStyle.Rows.Add(1, "vertical"); tableStyle.Rows.Add(2, "square"); tableStyle.Rows.Add(3, "panorama"); Display(tableStyle); // Create a second table, also using ID for PrimaryKey. DataTable tableSize = new DataTable("PictureSize"); var idColumnSize = new DataColumn("ID", typeof(int)); tableSize.Columns.Add(idColumnSize); tableSize.PrimaryKey = new DataColumn[] { idColumnSize }; tableSize.Columns.Add(new DataColumn("Size", typeof(int))); tableSize.Rows.Add(1, 50); tableSize.Rows.Add(2, 150); tableSize.Rows.Add(3, 250); Display(tableSize); // Merge the 2 tables together based on the PrimaryKey. tableStyle.Merge(tableSize); Display(tableStyle); } static void Display(DataTable table) { // Display merged table. Console.WriteLine("::TABLE::"); foreach (DataRow row in table.Rows) { Console.WriteLine("ROW: {0}", string.Join(",", row.ItemArray)); } } }

::TABLE:: ROW: 1,vertical ROW: 2,square ROW: 3,panorama ::TABLE:: ROW: 1,50 ROW: 2,150 ROW: 3,250 ::TABLE:: ROW: 1,vertical,50 ROW: 2,square,150 ROW: 3,panorama,250

Summary. DataTable is a powerful, convenient class. We can add columns and rows. DataTable is faster, in Windows Forms, than manually adding rows. It reduces complexity.