数据表VS数据视图

Question

Hy,我真的不明白datatable和dataview之间的区别,因为我们可以这样做:

   Dim dtb As New DataTable()
   Dim dtv As DataView = dtb.DefaultView

提前致谢 .

Answer 1

这Datatable是根据您的数据库中的查询提取的无序和未过滤的DataRows集合.
DataView(您可以拥有多个)是相同数据的过滤和/或有序视图.

例如:

 using(SqlConnection cn = GetConnection())
 {
     cn.Open();
     SqlDataAdapter da = new SqlDataAdapter("SELECT * FROM Customers", cn);
     DataTable dt = new DataTable();
     da.Fill(dt);

     // At this point dt is filled with datarows extracted from the database in no particular order 
     // And the DefaultView presents the same record organization (or lack of), but...

     // Order on the default view by CustomerName
     dt.DefaultView.Sort = "CustomerName";
     foreach(DataRowView rv in dt.DefaultView)
          Console.WriteLine(rv["CustomerName"].ToString();

     // A new dataview with only a certain kind of customers ordered by name
     DataView dvSelectedCust = new DataView(dt, "CreditLevel = 1", "CustomerName", DataViewRowState.Unchanged);
     foreach(DataRowView rv in dvSelectedCust)
          Console.WriteLine(rv["CustomerName"],ToString();



 }

当然,创建和维护DataView是对性能的一种打击,因此您可以选择仅在您真正需要时才使用它