C＃如何执行一个字符串，然后存储该结果？

Question

仅供参考，此页面（add.ashx.cs）是数据库的添加页面。

我试图做的是：

1. 弄清楚如何执行字符串queryID和queryID

的那么

店，结果我有点新意这，但这是我迄今为止正在处理的内容。我在正确的道路上，我应该改变什么？我不相信下面的代码包括存储结果，但只是执行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

在您的代码示例中有一些内容不匹配。第一个queryID是您的实际查询。其次，在SqlConnection中，您需要提供一个连接字符串，它连接到您的数据库（SQL Server，ACCESS，...）。一个有效的例子可能是这样的：

// 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，你执行一个阅读器，但只选择一个单一的值。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(); 

最后一件事。您应该在使用块中使用实现IDisposable的对象。这种方式将在不再需要时从内存中移除：

// 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(); 
}