Thursday, September 23, 2010

DataTable - Adding, Modifying, Deleting, Filtering, Sorting rows

 

 In this article, I am going to explain how to Add, Modify, Delete, Sort, Filter rows of the DataTable.

Introduction
DataTable is a central object in the ADO.NET library. If you are working with ADO.NET - accessing data from database, you can not escape from DataTable. Other objects that use DataTable are DataSet and DataView. In this tutorials, I will explain how to work with DataTable. I have tried to cover most of the frequently used activity in the DataTable, I hope you will like it

Creating a DataTable
To create a DataTable, you need to use System.Data namespace, generally when you create a new class or page, it is included by default by the Visual Studio. Lets write following code to create a DataTable object. Here, I have pased a string as the DataTable name while creating DataTable object.

// instantiate DataTable 
DataTable dTable = new DataTable("Dynamically_Generated");

Creating Columns in the DataTable
To create column in the DataTable, you need to use DataColumn object. Instantiate the DataColumn object and pass column name and its data type as parameter. Then call add method of DataTable column and pass the DataColumn object as parameter.

Specifying AutoIncrement column in the DataTable
To specify a column as AutoIncrement (naturally it should be an integer type of field only), you need to set some properties of the column like AutoIncrement, AutoIncrementSeed. See the code below, here I am setting the first column "AutoID" as autoincrement field. Whenever a new row will be added its value will automatically increase by 1 as I am specified AutoIncrementSeed value as 1.
// specify it as auto increment field
auto.AutoIncrement = true;
auto.AutoIncrementSeed = 1;
auto.ReadOnly = true;
If you want a particular column to be a unique column ie. you don't want duplicate records into that column, then set its Unique property to true like below.
auto.Unique = true;
Specifying Primary Key column in the DataTable
To set the primary key column in the DataTable, you need to create arrays of column and store column you want as primary key for the DataTable and set its PrimaryKey property to the column arrays. See the code below.
 
// create primary key on this field 
DataColumn[] pK = new DataColumn[1];
pK[0] = auto;
dTable.PrimaryKey = pK;

Till now we have created the DataTable, now lets populate the DataTable with some data.
Populating data into DataTable
There are two ways to populate DataTable.

Using DataRow object

Look at the code below, I have created a DataRow object above the loop and I am assiging its value to the dTable.NewRow() inside the loop. After specifying columns value, I am adding that row to the DataTable using dTable.Rows.Add method.

// populate the DataTable using DataRow objectDataRow row = null;
for (int i = 0; i < 5; i++)
{
     row = dTable.NewRow();
     row["AutoID"] = i + 1;
     row["Name"] = i + " - Ram";
     row["Address"] = "Ram Nagar, India - " + i;
     dTable.Rows.Add(row);}

Instead of using the column name, you can use ColumnIndex too, however it is not suggested as you might want to add a column in the mid of the table then you will need to change your code wherever you have specified the index of the column. Same applies while reading or writing values into Database column.

Asiging the value of column using Arrays

In following code, I have specified the values of every column as the array separated by comma (,) in the Add method of the dTable.Rows.
 
// manually adding rows using array of values 
dTable.Rows.Add(6, "Manual Data - 1", "Manual Address - 1, USA");
dTable.Rows.Add(7, "Manual Data - 2", "Manual Address - 2, USA");
Modifying data into DataTable
Modifying Row Data

To edit the data of the row, sets its column value using row index or by specifying the column name. In below example, I am updating the 3rd row of the DataTable as I have specified the row index as 2 (dTable.Rows[2]).

// modify certain values into the DataTabledTable.Rows[2]["AutoID"] = 20;
dTable.Rows[2]["Name"] = "Modified";
dTable.Rows[2]["Address"] = "Modified Address";
dTable.AcceptChanges();


Deleting Row

To delete a row into DataTable, call the rows.Delete() method followed by AcceptChanges() method. AcceptChanges() method commits all the changes made by you to the DataTable. Here Row[1] is the index of the row, in this case 2nd row will be deleted as in collection (here rows collection) count start from 0.

// Delete row 
dTable.Rows[1].Delete();
dTable.AcceptChanges();

Filtering data from DataTable
To filter records from the DataTable, use Select method and pass necessary filter expression. In below code, the 1st line will simply filter all rows whose AutoID value is greater than 5. The 2nd line of the code filters the DataTable whose AutoID value is greater than 5 after sorting it.
 
DataRow[] rows = dTable.Select(" AutoID > 5");
DataRow[] rows1 = dTable.Select(" AutoID > 5", "AuotID ASC");

Note that Select method of the DataTable returns the array of rows that matche the filter expression. If you want to loop through all the filtered rows, you can use foreach loop as shown below. In this code, I am adding all the filtered rows into another DataTable.
foreach (DataRow thisRow in rows)
{
     // add values into the datatable
     dTable1.Rows.Add(thisRow.ItemArray);}

Working with Aggregate functions 
We can use almost all aggregate functions with DataTable, however the syntax is bit different than standard SQL.
Suppose we need to get the maximum value of a particular column, we can get it in the following way.
 
DataRow[] rows22 = dTable.Select("AutoID = max(AutoID)");
string str = "MaxAutoID: " + rows22[0]["AutoID"].ToString();

To get the sum of a particular column, we can use Compute method of the DataTable. Compute method of the DataTable takes two argument. The first argument is the expression to compute and second is the filter to limit the rows that evaluate in the expression. If we don't want any filteration (if we need only the sum of the AutoID column for all rows), we can leave the second parameter as blank ("").
 
object objSum = dTable.Compute("sum(AutoID)", "AutoID > 7");
string sum = "Sum: " + objSum.ToString();
// To get sum of AutoID for all rows of the DataTable
object objSum = dTable.Compute("sum(AutoID)", "");

Sorting data of DataTable
Oops !. There is no direct way of sorting DataTable rows like filtering (Select method to filter DataRows).
There are two ways you can do this.

Using DataView

See the code below. I have created a DataView object by passing my DataTable as parameter, so my DataView will have all the data of the DataTable. Now, simply call the Sort method of the DataView and pass the sort expression. Your DataView object have sorted records now, You can either directly specify the Source of the Data controls object like GridView, DataList to bind the data or if you need to loop through its data you can use ForEach loop as below.

// Sorting DataTableDataView dataView = new DataView(dTable);
dataView.Sort = " AutoID DESC, Name DESC";
foreach (DataRowView view in dataView)
{

Response.Write(view["Address"].ToString());
}

Using DataTable.Select() method

Yes, you can sort all the rows using Select method too provided you have not specified any filter expression. If you will specify the filter expression, ofcourse your rows will be sorted but filter will also be applied. A small drawback of this way of sorting is that it will return array of DataRows as descibed earlier so if you are planning to bind it to the Data controls like GridView or DataList you will have for form a DataTable by looping through because directly binding arrays of rows to the Data controls will not give desired results.
 
DataRow[] rows = dTable.Select("", "AutoID DESC");

// create columns for the DataTable
DataColumn auto = new DataColumn("AutoID", typeof(System.Int32));
dTable.Columns.Add(auto);
// create another column
DataColumn name = new DataColumn("Name", typeof(string));
dTable.Columns.Add(name);
// create one more column
DataColumn address = new DataColumn("Address", typeof(string));
dTable.Columns.Add(address);

Hope this article will be useful. If you have any question, comments or
suggestions, please respond to this article. Thank you very much for
reading it and Happy DataTable 


Best Regards
Sumedh Borkar
.