Tài liệu The DataColumn Class pdf

The DataColumn Class You use an object of the DataColumn class to represent a column. You can also store multiple DataColumn objects in a DataRow. Table 11.6 shows some of the DataColumn properties. Table 11.6: DataColumn PROPERTIES PROPERTY TYPE DESCRIPTION AllowDBNull bool Gets or sets a bool value that indicates whether null values are allowed in this DataColumn object. The default is true. AutoIncrement bool Gets or sets a bool value that indicates whether the DataColumn object automatically increments the value of the column for new rows. The default is false. AutoIncrementSeed long Gets or sets the starting value for the DataColumn object. Applies only when the AutoIncrement property is set to true. The default is 0. AutoIncrementStep long Gets or sets the increment used. Applies only when the AutoIncrement property is set to true. The default is 1. Caption string Gets or sets the caption for the column. The caption for the column is shown in Windows forms. The default is null. ColumnName string Gets or sets the name of the DataColumn object. ColumnMapping MappingType Gets or sets the MappingType of the DataColumn object. This determines how a DataColumn is saved in an XML document using the WriteXml() method. DataType Type Gets or sets the .NET data type used to represent the column value stored in the DataColumn object. This can be Boolean, Byte, Char, DateTime, Decimal, Double, Int16, Int32, Int64, SByte, Single, String, TimeSpan, UInt16, or UInt64. DafaultValue object Gets or sets the default value for the DataColumn when new rows are created. When AutoIncrement is set to true, DefaultValue is not used. MaxLength int Gets or sets the maximum length of text that may be stored in a DataColumn object. The default is -1. Table 11.6: DataColumn PROPERTIES PROPERTY TYPE DESCRIPTION Ordinal int Gets the numeric position of the DataColumn object (0 is the first object). ReadOnly bool Gets or sets a bool value that indicates whether the DataColumn object can be changed once it has been added to a DataRow. The default is false. Table DataTable Gets the DataTable to which the DataColumn object belongs. Unique bool Gets or sets a bool value that indicates whether the DataColumn values in each DataRow object must be unique. The default is false. You'll see the use of some of these properties, methods, and events later in this chapter. . The DataColumn Class You use an object of the DataColumn class to represent a column. You can also store multiple DataColumn objects. Gets the numeric position of the DataColumn object (0 is the first object). ReadOnly bool Gets or sets a bool value that indicates whether the DataColumn