C# DataSet 與 DataTable 詳解 (7) — 欄位/主鍵/外鍵/資料列操作

新增欄位與約束

DataColumn col = dt.Columns.Add("newColumn", typeof(int));
col.AllowDBNull = false; col.MaxLength = 4; col.Unique = true;
dt.PrimaryKey = new DataColumn[] { dt.Columns["ID"] };
// 複合主鍵
dt.PrimaryKey = new DataColumn[] { dt.Columns["OrderID"], dt.Columns["ProductID"] };

外鍵約束

ForeignKeyConstraint fk = new ForeignKeyConstraint(
    ds.Tables["Customers"].Columns["CustomerID"],
    ds.Tables["Orders"].Columns["CustomerID"]);
ds.Tables["Orders"].Constraints.Add(fk);

修改 DataRow

DataRow dr = ds.Tables["Customer"].Rows.Find("ANTON");
if (dr != null) {
    dr.BeginEdit();
    dr["CompanyName"] = "newValue";
    dr["ContactName"] = "newValue2";
    dr.EndEdit();
}

• BeginEdit/EndEdit 緩衝修改，CancelEdit 可取消
• Find 需主鍵已設定

判斷 Null 與指派 DBNull

DataRow dr = ds.Tables["Customers"].Rows.Find("aaa");
if (dr.IsNull("ContactName")) { /* ... */ }
else dr["ContactName"] = DBNull.Value;