C＃如何執行一個字符串，然後存儲該結果？

Question

僅供參考，此頁面（add.ashx.cs）是數據庫的添加頁面。

我試圖做的是：

1. 弄清楚如何執行字符串queryID和queryID

的那麼

店，結果我有點新意這，但這是我迄今爲止正在處理的內容。我在正確的道路上，我應該改變什麼？我不相信下面的代碼包括存儲結果，但只是執行queryID。

// new query to get last ID value 
// store the command.executeNonQuery results into a variable 

string queryID = "SELECT TOP (1) IDENT_CURRENT('dbo.license_info') FROM dbo.license_info"; 
// first: look up how to execute queryID 
// then: store results of query^

// execute queryID? (section below) 
SqlConnection sqlConnection1 = new SqlConnection(queryID); 
SqlCommand cmd = new SqlCommand(); 
SqlDataReader reader; 
cmd.CommandText = "Select * FROM queryID"; 
cmd.CommandType = CommandType.Text; 
cmd.Connection = sqlConnection1; 

sqlConnection1.Open(); 

reader = cmd.ExecuteReader(); 
// data is accessible through the datareader object here 

sqlConnection1.Close(); 

Answer 1

在您的代碼示例中有一些內容不匹配。第一個queryID是您的實際查詢。其次，在SqlConnection中，您需要提供一個連接字符串，它連接到您的數據庫（SQL Server，ACCESS，...）。一個有效的例子可能是這樣的：

// this is just a sample. You need to adjust it to your needs 
    string connectionStr = "Data Source=ServerName;Initial Catalog=DataBaseName;Integrated Security=SSPI;"; 
    SqlConnection sqlConnection1 = new SqlConnection(connectionStr); 
    SqlCommand cmd = new SqlCommand(sqlConnection1); 
    SqlDataReader reader; 

    cmd.CommandText = "SELECT TOP (1) IDENT_CURRENT('dbo.license_info') FROM dbo.license_info"; 
    cmd.CommandType = CommandType.Text; 
    sqlConnection1.Open(); 

    reader = cmd.ExecuteReader(); 

    List<string> results = new List<string>(); 

    if(reader.HasRows) 
    { 
     while(reader.Read()) 
     { 
      results.Add(reader[0].ToString()); 
     } 
    } 

    sqlConnection1.Close(); 

另一件事是，你執行一個閱讀器，但只選擇一個單一的值。您可以完美地使用ExecuteScalar：

// this is just a sample. You need to adjust it to your needs 
string connectionStr = "Data Source=ServerName;Initial Catalog=DataBaseName;Integrated Security=SSPI;"; 
SqlConnection sqlConnection1 = new SqlConnection(connectionStr); 
SqlCommand cmd = new SqlCommand(sqlConnection1); 

cmd.CommandText = "SELECT TOP (1) IDENT_CURRENT('dbo.license_info') FROM dbo.license_info"; 
cmd.CommandType = CommandType.Text; 
sqlConnection1.Open(); 

string result = cmd.ExecuteScalar().ToString(); 

sqlConnection1.Close(); 

最後一件事。您應該在使用塊中使用實現IDisposable的對象。這種方式將在不再需要時從內存中移除：

// this is just a sample. You need to adjust it to your needs 
string connectionStr = "Data Source=ServerName;Initial Catalog=DataBaseName;Integrated Security=SSPI;"; 
using(SqlConnection sqlConnection1 = new SqlConnection(connectionStr)) 
{ 
    SqlCommand cmd = new SqlCommand(sqlConnection1); 

    cmd.CommandText = "SELECT TOP (1) IDENT_CURRENT('dbo.license_info') FROM dbo.license_info"; 
    cmd.CommandType = CommandType.Text; 
    sqlConnection1.Open(); 

    string result = cmd.ExecuteScalar().ToString(); 
}