什么是填充从数据库中一个DropDownList的正确方法? [英] What is the right way to populate a DropDownList from a database?
问题描述
我从填充SQL Server数据库DropDownList中,如下图所示。它工作正常,但我不知道这是一个很好的方式。有人可以阐明这个方法有些轻,并给予一定的改善呢?
私人无效LoadSubjects()
{
ddlSubjects.Items.Clear();
字符串selectSQL =SELECT SubjectID,主旨名称FROM Students.dbo.Subjects SqlConnection的CON =新的SqlConnection(的connectionString);
CMD的SqlCommand =新的SqlCommand(selectSQL,CON);
SqlDataReader的阅读器; 尝试
{
列表项的newitem =新的ListItem();
newItem.Text =<选择主题>中;
newItem.Value =0;
ddlSubjects.Items.Add(的newitem); con.Open();
读者= cmd.ExecuteReader();
而(reader.Read())
{
的newitem =新的ListItem();
newItem.Text =读卡器[主旨名称]的ToString()。
newItem.Value =读卡器[SubjectID]的ToString()。
ddlSubjects.Items.Add(的newitem);
}
reader.Close();
}
赶上(例外错误)
{
//去做
}
最后
{
con.Close();
}
}
您可以将DropDownList绑定到数据源(数据表,表,数据集,SqlDataSource的,等等)。
例如,如果你想使用一个DataTable:
ddlSubject.DataSource = subjectsTable;
ddlSubject.DataTextField =SubjectNamne;
ddlSubject.DataValueField =SubjectID;
ddlSubject.DataBind();
编辑 - 更完整的例子
私人无效LoadSubjects()
{ 数据表科目=新的DataTable(); 使用(SqlConnection的CON =新的SqlConnection(的connectionString))
{ 尝试
{
SqlDataAdapter的适配器=新的SqlDataAdapter(SELECT SubjectID,主旨名称FROM Students.dbo.SubjectsCON);
adapter.Fill(学科); ddlSubject.DataSource =科目;
ddlSubject.DataTextField =SubjectNamne;
ddlSubject.DataValueField =SubjectID;
ddlSubject.DataBind();
}
赶上(异常前)
{
//处理错误
} } //添加初始项目 - 所以即使从选项添加此
// DB没有成功加载
ddlSubject.Items.Insert(0,新的ListItem(&下;选择主体>中,0));}
要通过标记设置初始值,而不是code-背后,指定选项(S),并设置AppendDataBoundItems属性为true:
< ASP:DropDownList的ID =ddlSubject=服务器AppendDataBoundItems =真>
< ASP:ListItem的文本=<选择主题>中值=0/>
< / ASP:DropDownList的>
然后,您可以将DropDownList绑定到code-背后一个DataSource(只记得删除:
ddlSubject.Items.Insert(0,新的ListItem(<选择主题>中,0));
从code-后面,否则你将有两个,项目。
I am populating a DropDownList from a SQL Server database as shown below. It works fine, but I'm not sure it's a good way. Can someone shed some light on this method, and give some improvements?
private void LoadSubjects()
{
ddlSubjects.Items.Clear();
string selectSQL = "SELECT SubjectID,SubjectName FROM Students.dbo.Subjects";
SqlConnection con = new SqlConnection(connectionString);
SqlCommand cmd = new SqlCommand(selectSQL, con);
SqlDataReader reader;
try
{
ListItem newItem = new ListItem();
newItem.Text = "<Select Subject>";
newItem.Value = "0";
ddlSubjects.Items.Add(newItem);
con.Open();
reader = cmd.ExecuteReader();
while (reader.Read())
{
newItem = new ListItem();
newItem.Text = reader["SubjectName"].ToString();
newItem.Value = reader["SubjectID"].ToString();
ddlSubjects.Items.Add(newItem);
}
reader.Close();
}
catch (Exception err)
{
//TODO
}
finally
{
con.Close();
}
}
You could bind the DropDownList to a data source (DataTable, List, DataSet, SqlDataSource, etc).
For example, if you wanted to use a DataTable:
ddlSubject.DataSource = subjectsTable;
ddlSubject.DataTextField = "SubjectNamne";
ddlSubject.DataValueField = "SubjectID";
ddlSubject.DataBind();
EDIT - More complete example
private void LoadSubjects()
{
DataTable subjects = new DataTable();
using (SqlConnection con = new SqlConnection(connectionString))
{
try
{
SqlDataAdapter adapter = new SqlDataAdapter("SELECT SubjectID, SubjectName FROM Students.dbo.Subjects", con);
adapter.Fill(subjects);
ddlSubject.DataSource = subjects;
ddlSubject.DataTextField = "SubjectNamne";
ddlSubject.DataValueField = "SubjectID";
ddlSubject.DataBind();
}
catch (Exception ex)
{
// Handle the error
}
}
// Add the initial item - you can add this even if the options from the
// db were not successfully loaded
ddlSubject.Items.Insert(0, new ListItem("<Select Subject>", "0"));
}
To set an initial value via the markup, rather than code-behind, specify the option(s) and set the AppendDataBoundItems attribute to true:
<asp:DropDownList ID="ddlSubject" runat="server" AppendDataBoundItems="true">
<asp:ListItem Text="<Select Subject>" Value="0" />
</asp:DropDownList>
You could then bind the DropDownList to a DataSource in the code-behind (just remember to remove:
ddlSubject.Items.Insert(0, new ListItem("<Select Subject>", "0"));
from the code-behind, or you'll have two "" items.
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