I am working with Visual Studio 2010 and I added a new Item as report.mdf to my project as database; I created a table Table1 and I have added one record manually to the Table1; but when I try to select the data I can not do it and get this error:
invalid attempt to read when no data is present
This is my code:
SqlCommand objcomand = new SqlCommand();
SqlConnection con = new SqlConnection();
con.ConnectionString=#"Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Users\EHSAN\My Documents\Visual Studio 2010\Projects\report\report\App_Data\report.mdf;Integrated Security=True;User Instance=True";
objcomand.Connection = con;
objcomand.CommandText = "select * from Table1";
con.Open();
SqlDataReader reader1 = objcomand.ExecuteReader();
string i = reader1.GetValue(1).ToString();
con.Close();
You have to advance the DataReader to the next block of data with SqlDataReader.Read:
string i = null;
// use using for everything that implements IDisposable like a Connection or a DataReader
using(var reader1 = objcomand.ExecuteReader())
{
// a loop since your query can return multiple records
while(reader1.Read())
{
// if the field actually is the first you have to use GetString(0)
i = reader1.GetString(1);
}
}
Related
I'm working on an ASP.NET Web Application with Visual Studio 2010. My target framework is ".NET Framework 4" and I'm sending queries to a SQL Server 2008 database which version is "Microsoft SQL Server 2008 R2 (SP2)".
I'm connecting using the following connection string "Data Source=XXXX;Initial Catalog=XXXX;Integrated Security=False;User Id=XXXX;Password= XXXX;MultipleActiveResultSets=True" and sending queries with the code below:
public static List<DataTable> getData(String query)
{
var results = new List<DataTable>();
try
{
using (SqlConnection connection = new SqlConnection(ConnectionString))
{
using (SqlCommand command = new SqlCommand(query, connection))
{
connection.Open();
command.CommandTimeout = 0;
using (SqlDataReader reader = command.executeReader())
{
do
{
while (reader.Read()) ;
var dataTable = new DataTable();
dataTable.Load(reader);
results.Add(dataTable);
} while (reader.NextResult());
}
connection.Close();
}
}
}
}
The query I'm sending is an Stored Procedure which returns two tables, at first it had a loop which calls another Stored Procedure depending on some internal condition, creation and insertion on a tempdb..#table and two SELECT statements.
But now it only contains:
SELECT 1,2,3,4,5
SELECT 6,7,8,9,0
I don't know why but the reader.NextResult() is always false so I never get the second table result.
Does anyone know what I'm doing wrong? What should I do to receive and read the two results from the query?
if this is using a stored proc you need something like this: notice the command type
using (System.Data.SqlClient.SqlConnection conn = new System.Data.SqlClient.SqlConnection(myConnString))
{
using (System.Data.SqlClient.SqlCommand cmd = new System.Data.SqlClient.SqlCommand())
{
cmd.CommandText = "myMultipleTablesSP";
cmd.Connection = conn;
cmd.CommandType = CommandType.StoredProcedure;
conn.Open();
System.Data.SqlClient.SqlDataAdapter adapter = new System.Data.SqlClient.SqlDataAdapter(cmd);
DataSet ds = new DataSet();
adapter.Fill(ds);
conn.Close();
}
}
if for example you return 2 tables in your SP, like:
SELECT * FROM [TableA];
SELECT * FROM [TableB];
you would access this tables as:
DataTable tableA = ds.Tables[0];
DataTable tableB = ds.Tables[1];
OK, I have run some test and find out the problem is from dataTable.Load(reader); somehow and I don't know why and what is exactly happening behind that method.
but if you use
do {
while(reader.Read()) {
...
}
} while (reader.NextResult());
everything works as expected.
I have been writing a lot of open and close connection to a Microsoft SQL Server database. I'm not sure whether it is the latest technique available for .NET. Is there any latest .NET function that I'm missing?
Example code:
protected string InjectUpdateToProductDBString(string Command, TextBox Data, string TBColumn)
{
string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["AuthenticationDBConnectionString"].ConnectionString;
SqlConnection con = new SqlConnection(connectionString);
con.Open();
SqlCommand cmd = new SqlCommand(command, con);
cmd.Parameters.AddWithValue("#" + TBColumn, Data.Text.ToString());
cmd.ExecuteNonQuery();
con.Close();
return "Data successfully updated";
}
Is there any replacement for this fussy code technique? Just a discussion to improve my code technique.
There are other ways to write it and other tools you could use (like Entity Framework).
However, I recommend that you create a static function (or several) for your data access calls.
protected DataTable ExecuteSqlDataReader(string connection, string sqlQuery, SqlParameter[] cmdParams)
{
MySqlConnection con = new MySqlConnection(connection);
MySqlCommand cmd = new MySqlCommand(sqlQuery, con);
cmd.Parameters = cmdParams;
MySqlDataAdapter sda = new MySqlDataAdapter(cmd);
DataTable dt = new DataTable();
sda.Fill(dt);
sda.Command.Close();
return dt;
}
Create methods for Getting a dataTable, One value, ExecuteNonQuery, and even break it further down by abstracting out the SqlCommand creation to it's own method.
In any project, this code should be written only a few times.
Make sure that you enclose your SqlConnection in using statement. It will ensure the connection is closed even if there is an exception. Also, enclose your SqlCommand object in using statement, that will ensure disposal of unmanaged resources.
In your current code snippet if there is an exception at cmd.ExecuteNonQuery(); then your line con.Close would not execute, leaving the connection open.
So your method could be like:
protected string InjectUpdateToProductDBString(string Command, TextBox Data, string TBColumn)
{
string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["AuthenticationDBConnectionString"].ConnectionString;
using (SqlConnection con = new SqlConnection(connectionString))
{
con.Open();
using (SqlCommand cmd = new SqlCommand(command, con))
{
cmd.Parameters.AddWithValue("#" + TBColumn, Data.Text.ToString());
cmd.ExecuteNonQuery();
}
}
return "Data successfully updated";
}
Later you can return a DataTable or List<T> for your returned rows from the query.
If you want to move away from ADO.Net, then you can look into Object-Relation Mapping (ORM), which would provide you objects based on your database and easier way to manage your code base. Entity framework is one of them. You may see https://stackoverflow.com/questions/132676/which-orm-for-net-would-you-recommend
private SqlConnection GetConnection()
{
var con = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["AuthenticationDBConnectionString"].ConnectionString);
con.Open();
return con;
}
protected string InjectUpdateToProductDBString(string Command, TextBox Data, string TBColumn)
{
using (var con = GetConnection())
{
using (var cmd = con.CreateCommand())
{
cmd.Parameters.AddWithValue("#" + TBColumn, Data.Text);
cmd.ExecuteNonQuery();
return "Data Succesfully Updated";
}
}
}
I want to display the data that is selected in the SQL query , I tried to use ExecuteScalar() but it only work with 1 value , here is my c# code :
SqlConnection conn = new SqlConnection("Data Source=MAX-PC\\SQLEXPRESS;Initial Catalog=newSchool;Integrated Security=True");
SqlCommand cmd = new SqlCommand("view_profile", conn);
cmd.CommandText = "exec view_profile #posted_id";
cmd.Parameters.AddWithValue("#posted_id", WebForm1.x);
conn.Open();
cmd.ExecuteNonQuery;
conn.Close();
and that's the proc :
CREATE PROC view_profile
#posted_in INTEGER
AS
BEGIN
SELECT P.poster , P.post_description
FROM Posts P
WHERE P.posted_in = #posted_in
END
you are a little confused:
ExecuteScalar(): Executes the query, and returns the first column of the first row in the result set returned by the query. Additional columns or rows are ignored.
ExecuteNonQuery(): Executes a Transact-SQL statement against the connection and returns the number of rows affected, it is intended for UPDATE, INSERT and DELETE queries
What you need is ExecuteReader()
using (SqlConnection connection = new SqlConnection(connectionString))
{
connection.Open();
SqlCommand command = new SqlCommand(queryString, connection);
SqlDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Console.WriteLine(String.Format("{0}", reader[0]));
}
}
this code is successfully inserting a new value in a SQL db, but only when I insert constant values.
I need help where it says **(?)** in the code below, where I want to insert new values without specifying constants in the code.
What I mean is, I want to be able to type any random value in output window and it gets inserted into the SQL db.
private void InsertInfo()
{
String strConnection = "Data Source=HP\\SQLEXPRESS;database=MK;Integrated Security=true";
SqlConnection con = new SqlConnection(strConnection);
string connetionString = null;
SqlConnection connection ;
SqlDataAdapter adapter = new SqlDataAdapter();
connetionString = #"Data Source=HP\SQLEXPRESS;database=MK;Integrated Security=true";
connection = new SqlConnection(connetionString);
string sql = "insert into record (name,marks) **values( ?))";**
try
{
connection.Open();
adapter.InsertCommand = new SqlCommand(sql, connection);
adapter.InsertCommand.ExecuteNonQuery();
MessageBox.Show ("Row inserted !! ");
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
}
}
private void insert_Click(object sender, EventArgs e)
{
InsertInfo();
}
There is no need to use an adapter here; that is not helping you. Just:
var name = ...
var marks = ...
using(var conn = new SqlConnection(connectionString))
using(var cmd = conn.CreateCommand()) {
cmd.CommandText = "insert into record (name, marks) values (#name, #marks)";
cmd.Parameters.AddWithValue("name", name);
cmd.Parameters.AddWithValue("marks", marks);
conn.Open();
cmd.ExecuteNonQuery();
}
or with a tool like "dapper":
var name = ...
var marks = ...
using(var conn = new SqlConnection(connectionString)) {
conn.Open();
conn.Execute("insert into record (name, marks) values (#name, #marks)",
new {name, marks});
}
Those '?' are termed as parameters. From what I understand, you are wanting to use a parametrized query for your insert which is a good approach as they save you from chance of a SQL injection. The '?' sing in your query is used when you are using an
OLEDBConnection & Command object.
Normally, you would use '#' symbol to specify a parameter in your query. There is no need for an adapter. You just
//Bind parameters
// Open your Connection
// Execute your query
// Close connection
// return result
Parametrized queries 4 Guys from Rolla
MSDN: How to Protect from SQL injection in ASP.NET
I have am OLEDB Connection configured in the connection managers and I want to use it in a SCRIPT. The script needs to call a stored proc and then create buffer rows. I have added the connection to the connections available to the script and this is my code.
Boolean fireagain = true;
SqlConnection conn = new SqlConnection();
conn = (SqlConnection)(Connections.Connection
.AcquireConnection(null) as SqlConnection);
SqlCommand cmd = new SqlCommand();
conn.Open();
ComponentMetaData.FireInformation(
0, "Script", "Connection Open", string.Empty, 0, ref fireagain);
cmd.Connection = conn;
cmd.CommandText = "up_FullTextParser_select" ;
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("Phrase", DbType.String).Value = Row.Keywords;
cmd.Parameters.AddWithValue("SpecialTerm", DbType.String).Value = "Exact match";
cmd.Parameters.AddWithValue("StopListId", DbType.Int32).Value = 0;
SqlDataReader rdr = cmd.ExecuteReader(CommandBehavior.CloseConnection);
while (rdr.Read())
{
TermsBuffer.AddRow();
TermsBuffer.Term = rdr[0].ToString();
}
conn.Close();
Anyway, it seems to fail on the AcquireConnection. Am I converting this wrong? Should I be using a different way to using the connections defined outside the script?.
You cannot cast an OLEDB connection to SqlConnection object. You must use the OleDbConnection object. See the example - http://blogs.msdn.com/b/mattm/archive/2008/08/22/accessing-oledb-connection-managers-in-a-script.aspx
This MSDN example implies that you using AcquireConnection incorrectly.
You need to use a managed connection provider.
If you insist on using an OLEDB connection, you cannot use AcquireConnection but you can extract the connection string and then use it to create an OLEDB connection:
string connstr = Dts.Connections["my_OLEDB_connection"].ConnectionString;
System.Data.OleDb.OleDbConnection objConn = new System.Data.OleDb.OleDbConnection(connstr);
This may not work if the connection string is created via an expression of some sort.
IDTSConnectionManager100 connMgr = this.Connections.ADONetAppStaging ; //this we need to give name in connection manager in script component
SqlConnection myADONETConnection = new SqlConnection();
myADONETConnection = (SqlConnection)(connMgr.AcquireConnection(null));
//Read data from table or view to data table
string query = "Select top 10 * From ##AP_Stagging_Temp_ExportWODuplicates Order by 1,2,3 asc ";
// string query = "Select * From ##AP_Stagging_Temp_For_JLL_ExportWODuplicates order by 1,2,3 asc ";
SqlDataAdapter adapter = new SqlDataAdapter(query, myADONETConnection);
datatable dtExcelData = new datatable();
adapter.Fill(dtExcelData);
myADONETConnection.Close();