ADO.NET對象的構造(4)_DataColumn(續)
2024-07-10 12:59:38
供稿：網友
n overloads public overridable function add() as datacolumn
n overloads public sub add(byval column as datacolumn)
n overloads public overridable function add(byval columnname as string) as datacolumn
n overloads public overridable function add(byval columnname as string, byval type as type) as datacolumn
n overloads public overridable function add(byval columnname as string, byval type as type,byval expression as string) as datacolumn
參數
1. columnname 列的名稱。
2. column 要添加的 datacolumn。
3. type 新列的 datatype。
4. expression 要分配給 expression 屬性的表達式。
datacolumncollection 定義 datatable 的架構，并確定每個 datacolumn 可以包含什么種類的數據。可以通過 datatable對象的 columns 屬性訪問 datacolumncollection。
datacolumncollection 使用 add 和 remove 方法插入和刪除 datacolumn 對象。使用 count 屬性確定集合中有多少 datacolumn 對象。使用 contains 方法驗證集合中是否存在指定索引或列名稱。
示例
private sub addcolumn()
dim cols as datacolumncollection= dataset1.tables("orders").columns
dim mycol as datacolumn
mycol = cols.add()
with mycol
.datatype = system.type.gettype("system.decimal")
.columnname = "total"
.expression = "unitprice * quantity"
.readonly = true
.unique = false
end with
mycol = new datacolumn
with mycol
.datatype = system.type.gettype("system.decimal")
.columnname = "total"
.expression = "unitprice * quantity"
.readonly = true
.unique = false
end with
cols.add(mycol)
mycol = cols.add("total", system.type.gettype("system.decimal"), "unitprice * quantity")
mycol.readonly = true
mycol.unique = false
mycol = cols.add("total")
with mycol
.datatype = system.type.gettype("system.decimal")
.readonly = true
.expression = "unitprice * quantity"
.unique = false
end with
mycol = cols.add("total", system.type.gettype("system.decimal"))
mycol.expression = "unitprice * quantity"
mycol.readonly = true
mycol.unique = false
dim col as datacolumn
for each col in cols
console.writeline(col.columnname)
console.writeline(col.datatype.tostring)
next
end sub
