从 C# 代码更改连接字符串？

Question

有没有办法以编程方式更改连接字符串？我的意思是用户可以使用组合框选择他想使用的网站，然后在该特定网站上加载用户？

配置代码如下

<add key ="sampleconnectionstring" value="Server=sampleserver;Database=sampledb;User ID=sampleid;Password=samplepassword;Trusted_Connection=False;Encrypt=True;"/>
<add key ="sampleconnectionstring1" value="Server=sampleserver1;Database=sampledb1;User ID=sampleid1;Password=samplepassword;Trusted_Connection=False;Encrypt=True;"/>
<add key ="sampleconnectionstring2" value="Server=sampleserver2;Database=sampledb2;User ID=sampleid2;Password=;Trusted_Connection=False;Encrypt=True;"/>
<add key ="sampleconnectionstring3" value="Server=sampleserver3;Database=sampledb3;User ID=sampleid3;Password=samplepasswrd;Trusted_Connection=False;Encrypt=True;"/>

是否有一种编程方式（如果这是一个词）根据组合框中的所选项目在此连接字符串之间进行更改？任何帮助，将不胜感激。谢谢。

Answer 1

根据您使用的数据库，您可以在加载时加载所需的任何连接字符串。

以实体框架为例

Entities model = new Entities(connectionString);

对于 ADO.NET

  using (SqlConnection connection =
        new SqlConnection(connectionString))
    {

    }

对于 Linq To SQL

用途：

MyDataClassesDataContext db = new MyDataClassesDataContext(dynamicConnString);

对于 LinqDataSource，拦截 ContextCreating 事件，如上手动创建 DataContext：

protected void LinqDataSource_ContextCreating(object sender, LinqDataSourceContextEventArgs e)
{
    e.ObjectInstance = new MyDataClassesDataContext (dynamicConnString);
}

（Linq to SQL 示例取自：Linq to Sql - Set connection string dynamically based on environment variable

Answer 2

如果每个键与您的组合框项目之一的值相等，您可以直接通过键选择连接字符串。

Answer 3

您可以使用configurationmanager connectionstring collection 获取列表。 然后您可以将组合框绑定到它。类似：

<ComboBox ItemsSource={Binding ConnectionStrings} DisplayMemberPath="Name" SelectedItem={Binding Path=SelectedConnectionString, Mode=TwoWay} /> 

Answer 4

请记住，连接字符串只是一个字符串。您可以将其他字符串连接到它：

string CreateConnectionString(string server, string sampledb,  string userid, string password)
{
   return string.Format("Server={0};Database={1};User ID={2};Password={3}Trusted_Connection=False;Encrypt=True;",server,sampledb,userid,password);

}

Answer 5

有办法，只需在 Combobox selectedindex changed 事件上设置连接字符串。请参阅下面的代码。首先将默认连接字符串设置为 appconfig 中的第一个字符串，因为在表单加载时 selectedindexchanged 事件不会触发。随时随地获取连接的 ConnString，因为它是一个可以访问的公共属性。

    public string ConnString { get; set; }
    private void ComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        if (CBox.SelectedIndex == 0)
        {
            ConnString = getAppSetting("sampleconnectionstring");
        }
        else if (CBox.SelectedIndex == 1)
        {
            ConnString = getAppSetting("sampleconnectionstring1");
        }
        else if (CBox.SelectedIndex == 2)
        {
            ConnString = getAppSetting("sampleconnectionstring2");
        }
        else if (CBox.SelectedIndex == 3)
        {
            ConnString = getAppSetting("sampleconnectionstring3");
        }
    }
    private string getAppSetting(string strKey)
    {
        string strValue = string.Empty;
        XmlReaderSettings settings = new XmlReaderSettings();
        settings.XmlResolver = new XmlXapResolver();
        XmlReader reader = XmlReader.Create("ServiceReferences.ClientConfig");
        reader.MoveToContent();
        while (reader.Read())
        {
            if (reader.NodeType == XmlNodeType.Element && reader.Name == "add")
            {
                if (reader.HasAttributes)
                {
                    strValue = reader.GetAttribute("key");
                    if (!string.IsNullOrEmpty(strValue) && strValue == strKey)
                    {
                        strValue = reader.GetAttribute("value");
                        return strValue;
                    }
                }
            }
        }
        return strValue;
    }

    private void LayoutRoot_Loaded(object sender, RoutedEventArgs e)
    {
        ConnString = getAppSetting("sampleconnectionstring");

    }

Answer 6

如果我没记错的话，你一定是在 web.config 文件中这样做的。

<appSettings>
     <add key = "sampleconnectionstring" ..../>
     <add key = "sampleconnectionstring1" ..../>
     <add key = "sampleconnectionstring2" ..../>
     <add key = "sampleconnectionstring3" ..../>
</appSettings>

你想以编程方式更改字符串。

所以，你可以这样做---- 首先，您可以将键名保留在组合框的值字段中。 然后，在下拉/组合框中选择的索引更改为如下所示...

  protected void ddlUrDropdown_SelectedIndexChanged(object sender, EventArgs e)
  {
        // Checking whether first Item "Select......." (index = 0) is selected or not.
        if (ddlUrDropdown.SelectedIndex != 0)
        {
            // Getting the Selected "Country_Id".
            string keyName = ddlUrDropdown.SelectedValue;
            string connectionString = ConfigurationSettings.AppSettings[keyName];
            // Where keyName can take values like- "sampleconnectionstring" or "sampleconnectionstring1" or "sampleconnectionstring2" or "sampleconnectionstring3"
            // After getting the connection string according to selected item of combo box, u can create connection and do whatever u want, like below...
            using(SqlConnection connection = new SqlConnection(connectionString))
            {
                  connection.Open();
                  // perform work with connection
             }         
        }
        // Error Message displayed when first Item "Select......." (index = 0) is selected.
        else
        {
            lblError.Text = "Select any item .";
        }
    }