System.Data Namespace Component

The System.Data namespace provides access to classes that represent the ADO.NET architecture. ADO.NET lets you build components that efficiently manage data from multiple data sources.

DataColumn Class

Definition

Namespace:: System.Data

Assemblies:: System.Data.dll, netstandard.dll, System.Data.Common.dll

Represents the schema of a column in a DataTable.

Examples

The following example creates a DataTable with several DataColumn objects.

private void MakeTable()
{ 
    // Create a DataTable. 
    DataTable table = new DataTable("Product");

    // Create a DataColumn and set various properties. 
    DataColumn column = new DataColumn(); 
    column.DataType = System.Type.GetType("System.Decimal"); 
    column.AllowDBNull = false; 
    column.Caption = "Price"; 
    column.ColumnName = "Price"; 
    column.DefaultValue = 25; 

    // Add the column to the table. 
    table.Columns.Add(column); 

    // Add 10 rows and set values. 
    DataRow row; 
    for(int i = 0; i < 10; i++)
    { 
        row = table.NewRow(); 
        row["Price"] = i + 1; 

        // Be sure to add the new row to the 
        // DataRowCollection. 
        table.Rows.Add(row); 
    } 
}

Remarks

The DataColumn is the fundamental building block for creating the schema of a DataTable. You build the schema by adding one or more DataColumn objects to the DataColumnCollection. For more information, see Adding Columns to a DataTable.

Each DataColumn has a DataType property that determines the kind of data the DataColumn contains. For example, you can restrict the data type to integers, or strings, or decimals. Because data that is contained by the DataTable is typically merged back into its original data source, you must match the data types to those in the data source. For more information, see Data Type Mappings in ADO.NET.

Properties such as AllowDBNull, Unique, and ReadOnly put restrictions on the entry and updating of data, thereby helping to guarantee data integrity. You can also use the AutoIncrement, AutoIncrementSeed, and AutoIncrementStep properties to control automatic data generation. For more information about AutoIncrement columns, see Creating AutoIncrement Columns. For more information, see Defining Primary Keys.

You can also make sure that values in a DataColumn are unique by creating a UniqueConstraint and adding it to the ConstraintCollection of the DataTable to which the DataColumn belongs. For more information, see DataTable Constraints.

To create a relation between DataColumn objects, create a DataRelation object and add it to the DataRelationCollection of a DataSet.

You can use the Expression property of the DataColumn object to calculate the values in a column, or create an aggregate column. For more information, see Creating Expression Columns.

Constructors

DataColumn()	Initializes a new instance of a DataColumn class as type string.
DataColumn(String)	Initializes a new instance of the DataColumn class, as type string, using the specified column name.
DataColumn(String, Type)	Initializes a new instance of the DataColumn class using the specified column name and data type.
DataColumn(String, Type, String)	Initializes a new instance of the DataColumn class using the specified name, data type, and expression.
DataColumn(String, Type, String, MappingType)	Initializes a new instance of the DataColumn class using the specified name, data type, expression, and value that determines whether the column is an attribute.

Properties

AllowDBNull	Gets or sets a value that indicates whether null values are allowed in this column for rows that belong to the table.
AutoIncrement	Gets or sets a value that indicates whether the column automatically increments the value of the column for new rows added to the table.
AutoIncrementSeed	Gets or sets the starting value for a column that has its AutoIncrement property set to true. The default is 0.
AutoIncrementStep	Gets or sets the increment used by a column with its AutoIncrement property set to true.
Caption	Gets or sets the caption for the column.
ColumnMapping	Gets or sets the MappingType of the column.
ColumnName	Gets or sets the name of the column in the DataColumnCollection.
Container	Gets the container for the component. (Inherited from MarshalByValueComponent)
DataType	Gets or sets the type of data stored in the column.
DateTimeMode	Gets or sets the DateTimeMode for the column.
DefaultValue	Gets or sets the default value for the column when you are creating new rows.
DesignMode	Gets a value indicating whether the component is currently in design mode. (Inherited from MarshalByValueComponent)
Events	Gets the list of event handlers that are attached to this component. (Inherited from MarshalByValueComponent)
Expression	Gets or sets the expression used to filter rows, calculate the values in a column, or create an aggregate column.
ExtendedProperties	Gets the collection of custom user information associated with a DataColumn.
MaxLength	Gets or sets the maximum length of a text column.
Namespace	Gets or sets the namespace of the DataColumn.
Ordinal	Gets the (zero-based) position of the column in the DataColumnCollection collection.
Prefix	Gets or sets an XML prefix that aliases the namespace of the DataTable.
ReadOnly	Gets or sets a value that indicates whether the column allows for changes as soon as a row has been added to the table.
Site	Gets or sets the site of the component. (Inherited from MarshalByValueComponent)
Table	Gets the DataTable to which the column belongs to.
Unique	Gets or sets a value that indicates whether the values in each row of the column must be unique.

Methods

CheckNotAllowNull()	This member supports the .NET Framework infrastructure and is not intended to be used directly from your code.
CheckUnique()	This member supports the .NET Framework infrastructure and is not intended to be used directly from your code.
Dispose()	Releases all resources used by the MarshalByValueComponent. (Inherited from MarshalByValueComponent)
Dispose(Boolean)	Releases the unmanaged resources used by the MarshalByValueComponent and optionally releases the managed resources. (Inherited from MarshalByValueComponent)
Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
GetHashCode()	Serves as the default hash function. (Inherited from Object)
GetService(Type)	Gets the implementer of the IServiceProvider. (Inherited from MarshalByValueComponent)
GetType()	Gets the Type of the current instance. (Inherited from Object)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
OnPropertyChanging(PropertyChangedEventArgs)	This member supports the .NET Framework infrastructure and is not intended to be used directly from your code.
RaisePropertyChanging(String)	This member supports the .NET Framework infrastructure and is not intended to be used directly from your code.
SetOrdinal(Int32)	Changes the ordinal or position of the DataColumn to the specified ordinal or position.
ToString()	Gets the Expression of the column, if one exists.

Events

Disposed

Adds an event handler to listen to the Disposed event on the component.

(Inherited from MarshalByValueComponent)

Applies to

.NET Core

3.0 Preview 8 2.2 2.1 2.0

.NET Framework

4.8 4.7.2 4.7.1 4.7 4.6.2 4.6.1 4.6 4.5.2 4.5.1 4.5 4.0 3.5 3.0 2.0 1.1

.NET Standard

2.1 Preview 2.0

Xamarin.Android

7.1

Xamarin.iOS

10.8

Xamarin.Mac

3.0

Thread Safety

This type is safe for multithreaded read operations. You must synchronize any write operations.

Examples

Examples of DataColumn Class

ASP.NET Code Input:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
    <head>
       <title>Sample Page</title>
       <meta http-equiv="Content-Type" content="text/html;charset=utf-8">
       <script runat="server" >
           Sub Page_Load()
               Dim xstr As String
               Dim xconn As New System.Data.OleDb.OleDbConnection
               xconn.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=T:\test.mdb;User Id=admin;Password=;"
               xconn.Open()
               xstr = xstr + "Connection xconn to database test.mdb  is opened successfully.<br />"
               Dim xdata As New System.Data.DataSet
               Dim xadapt As System.Data.OleDb.OleDbDataAdapter
               Dim sql As String = "SELECT * FROM T1"
               xadapt = New System.Data.OleDb.OleDbDataAdapter(sql, xconn)
               xstr = xstr + "Dataadapter xadapt is assigned to SELECT * FROM T1 through xconn successfully.<br />"
               xadapt.Fill(xdata,"T1")
               xstr = xstr + "Dataset xdata is filled by xadapt.fill successfully.<br />"
               xstr = xstr + "<br />"
               Dim xcol As System.Data.DataColumn
               xstr = xstr + "Declare a table column, xcol<br />"
               xcol = xdata.tables(0).Columns(0)
               xstr = xstr + "Assign xdata.tables(0).Columns(0) to table column, xcol <br />"
               xstr = xstr  + "->xcol.ColumnName: " + xcol.ColumnName + "<br />"
               xstr = xstr  + "->xcol.Caption: " + xcol.Caption + "<br />"
               xstr = xstr  + "->xcol.Ordinal: " + xcol.Ordinal.ToString + "<br />"
               xstr = xstr  + "->xcol.DataType: " + xcol.DataType.ToString + "<br />"
               xstr = xstr  + "->xcol.MaxLength: " + xcol.MaxLength.ToString + "<br />"
               xstr = xstr  + "->xcol.DefaultValue: " + xcol.DefaultValue + "<br />"
               xstr = xstr  + "->xcol.AllowDBNull: " + xcol.AllowDBNull.ToString + "<br />"
               
               xstr = xstr + "<br />"
               xadapt.Dispose()
               xstr = xstr + "Dataadapter xadapt is disposed successfully.<br />"
               xconn.Close()
               xstr = xstr + "Connection xconn is closed successfully.<br />"
               xstr = xstr + "Dataset xdata.tables(T1).rows(0).item(1):" + xdata.Tables("T1").Rows(0).Item("f1") + "<br />"
               xdata.Dispose()
               xstr = xstr + "Dataset xdata is disposed successfully.<br />"
               
               lbl01.Text = xstr
           End Sub
       </script>
    </head>
    <body>
<%Response.Write("<p>Results on "& Request.ServerVariables("SERVER_SOFTWARE") & " .net: " & System.Environment.Version.ToString & " " & ScriptEngine & " Version " & ScriptEngineMajorVersion & "." & ScriptEngineMinorVersion & "</p>")%>
       <% Response.Write ("<h1>This is a Sample Page of DataColumn Class</h1>") %>
       <p>
           <%-- Set on Page_Load --%>
           <asp:Label id="lbl01" runat="server" />
       </p>
    </body>
</html>

HTML Web Page Embedded Output: