DataColumn. A DataTable is represented by several types. In the table, a column represents the name and type of one cell in every row. This is called a DataColumn.
Class use. We use DataColumns in a DataTable with the GetType argument to create typed, and validated, relational data in memory. We can add and loop over columns.
Example. In the first statements, we create a DataTable and adds 3 columns to it. Internally the DataTable creates DataColumn instances—but we do not see them here.
Next We create a DataColumn object instance explicitly. We use the New DataColumn constructor.
Argument 1 This constructor receives two arguments. The first argument is the name of the column—a String.
Argument 2 The second argument is the type of the column. This is specified with the return value of GetType.
Detail In the For-Each loop, we use the Columns property on the DataTable. And we print the name and DataType for each column.
Module Module1
Sub Main()
' Create DataTable and add columns.
Dim table As DataTable = New DataTable()
table.Columns.Add("Dosage", GetType(Integer))
table.Columns.Add("Medication", GetType(String))
table.Columns.Add("Patient", GetType(String))
' Add a column object in a different way.
Dim column As DataColumn = New DataColumn("Appointment", GetType(DateTime))
table.Columns.Add(column)
' Add some rows.
table.Rows.Add(32, "Combivent", "Jane", DateTime.Now)
table.Rows.Add(100, "Dilantin", "Mark", DateTime.Now)
' Loop over columns.For Each c As DataColumn In table.Columns
Console.WriteLine("{0} = {1}", c, c.DataType)
Next
End Sub
End ModuleDosage = System.Int32
Medication = System.String
Patient = System.String
Appointment = System.DateTime
Indexer. Internally the DataTable type is implemented with Hashtable. This provides a fast way to access DataColumns by their names. This can be done with the indexer syntax.
A summary. A DataColum is an essential part of a DataTable. For rows and data to be added to a DataTable, columns must first exist, and they must match the data added.
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This page was last updated on Sep 27, 2022 (edit link).