DataColumn Class

Definition

Represents the schema of a column in a DataTable.

public class DataColumn : System.ComponentModel.MarshalByValueComponent
Inheritance

Inherited Members

System.ComponentModel.MarshalByValueComponent

System.Object

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); 
    } 
}
Private Sub MakeTable()
    ' Create a DataTable. 
    Dim table As DataTable = new DataTable("Product") 

    ' Create a DataColumn and set various properties. 
    Dim column As DataColumn = 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. 
    Dim row As DataRow 
    Dim i As Integer  
    For i = 0 to 9 
        row = table.NewRow() 
        row("Price") = i + 1 

        ' Be sure to add the new row to 
        ' the DataRowCollection. 
        table.Rows.Add(row) 
    Next i 
End Sub

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.

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.

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.

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.

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.

Thread Safety

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