[英]Don't close SQL connection until is has finished reading
我有下面的代码,它可以工作,但是只读取数据库的第一行,然后终止。 该数组应保存3个数据,但只能保存一个。
我认为这是因为它没有循环。
您如何说代码继续运行直到没有更多数据可读取?
SqlConnection conn1 = new SqlConnection(ssConnectionString);
conn1.Open();
SqlCommand command1 = conn1.CreateCommand();
command1.CommandText = "SELECT FeedURL FROM [dbo].[Feeds]";
rssFeeds.Add(command1.ExecuteScalar());
conn1.Close();
默认情况下, ExecuteScalar()
将仅返回一个值。 您将需要创建一个DataReader
,然后使用command1.ExecuteReader()
遍历结果。
您可以只使用ExecuteReader解决您的问题。 在本例中,我从MSDN取得的示例正在使用using语句来消耗连接,因为SqlConnection类具有一些非托管资源。 如果您对使用和终结器还有其他疑问,请在此处检查。
如何使用ExecuteReader,可以在这里检查:
static void HasRows(SqlConnection connection)
{
using (connection)
{
SqlCommand command = new SqlCommand(
"SELECT CategoryID, CategoryName FROM Categories;",
connection);
connection.Open();
SqlDataReader reader = command.ExecuteReader();
if (reader.HasRows)
{
while (reader.Read())
{
Console.WriteLine("{0}\t{1}", reader.GetInt32(0),
reader.GetString(1));
}
}
else
{
Console.WriteLine("No rows found.");
}
reader.Close();
}
}
conn1.Open();
string query = "select feedurl from [dbo].[feeds]";
DataSet DS = new DataSet();
SqlDataAdapter adapt = new SqlDataAdapter(query,conn1);
adapt.Fill(DS);
if (DS != null)
{
if (DS.Tables[0].rows.Count > 0 )
{
foreach(DataRow DR in DS.Tables[0].Rows)
{
string temp = DR['columnname'];
}
}
{
尝试这个:
//method to make this code reusable
//the returned data set is accessible even if the underlying connection is closed
//NB: that means data's held in memory; so beware of your resource usage
public DataSet ExecuteSQLToDataSet(string ssConnectionString, string query, string name)
{
DataSet ds = new DataSet("Tables");
using (SqlConnection conn1 = new SqlConnection(ssConnectionString))
{
conn1.Open();
SqlDataAdapter sda = new SqlDataAdapter(query, objConn);
sda.FillSchema(ds, SchemaType.Source, name);
sda.Fill(ds, name);
} //using statement will close and dispose the connection for you
return ds;
}
//example usage
DataSet ds = ExecuteSQLToDataSet(ssConnectionString, "SELECT FeedURL FROM [dbo].[Feeds]", "Feeds"); //nb: name doesn't have to match table name; you can call it what you like; naming is useful if you wanted to add other result sets to the same data set
//DataTable tblFeeds = ds.Tables["Feeds"]; //if you want to access the above query by name
foreach (DataTable tbl in ds.Tables)
{
foreach (DataRow dr in tbl.Rows) //tblFeeds.Rows if you did that instead of looping through all tables
{
//Console.WriteLine(dr["FeedURL"].ToString()); //you can specify a named column
Console.WriteLine(dr[0].ToString()); //or just use the index
}
}
Console.WriteLine("Done");
Console.ReadLine();
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