I'm trying to get the SQL result in a C# string variable or string array. Is it possible? Do I need to use SqlDataReader in some way?
I'm very new to C# functions and all, used to work in PHP, so please give a working example if you can (If relevant I can already connect and access the database, insert and select.. I just don't know how to store the result in a string variable).
This isn't the single greatest example in history, as if you don't return any rows from the database you'll end up with an exception, but if you want to use a stored procedure from the database, rather than running a SELECT statement straight from your code, then this will allow you to return a string:
public string StringFromDatabase()
{
SqlConnection connection = null;
try
{
var dataSet = new DataSet();
connection = new SqlConnection("Your Connection String Goes Here");
connection.Open();
var command = new SqlCommand("Your Stored Procedure Name Goes Here", connection)
{
CommandType = CommandType.StoredProcedure
};
var dataAdapter = new SqlDataAdapter { SelectCommand = command };
dataAdapter.Fill(dataSet);
return dataSet.Tables[0].Rows[0]["Item"].ToString();
}
catch (Exception ex)
{
throw new Exception(ex.Message, ex);
}
finally
{
if (connection != null)
{
connection.Close();
}
}
}
It can definitely be improved, but it would give you a starting point to work from if you want to go down a stored procedure route.
Try This:
SqlConnection con=new SqlConnection("/*connection string*/");
SqlCommand SelectCommand = new SqlCommand("SELECT email FROM table1", con);
SqlDataReader myreader;
con.Open();
myreader = SelectCommand.ExecuteReader();
List<String> lstEmails=new List<String>();
while (myreader.Read())
{
lstEmails.Add(myreader[0].ToString());
//strValue=myreader["email"].ToString();
//strValue=myreader.GetString(0);
}
con.Close();
accessing the Emails from list
lstEmails[0]->first email
lstEmails[1]->second email
...etc.,
You could use an SQL Data Reader:
string sql = "SELECT email FROM Table WHERE Field = #Parameter";
string variable;
using (var connection = new SqlConnection("Your Connection String"))
using (var command = new SqlCommand(sql, connection))
{
command.Parameters.AddWithValue("#Parameter", someValue);
connection.Open();
using (var reader = command.ExecuteReader())
{
//Check the reader has data:
if (reader.Read())
{
variable = reader.GetString(reader.GetOrdinal("Column"));
}
// If you need to use all rows returned use a loop:
while (reader.Read())
{
// Do something
}
}
}
Or you could use SqlCommand.ExecuteScalar()
string sql = "SELECT email FROM Table WHERE Field = #Parameter";
string variable;
using (var connection = new SqlConnection("Your Connection String"))
using (var command = new SqlCommand(sql, connection))
{
command.Parameters.AddWithValue("#Parameter", someValue);
connection.Open();
variable = (string)command.ExecuteScalar();
}
This May help you For MySQL
MySqlDataReader reader = mycommand.ExecuteReader();
while (reader.Read())
{
TextBox2.Text = reader.ToString();
}
For SQL
using (SqlCommand command = new SqlCommand("*SELECT QUERY HERE*", connection))
{
//
// Invoke ExecuteReader method.
//
SqlDataReader reader = command.ExecuteReader();
while (reader.Read())
{
TextBox2.Text = reader.GetString(0);
}
}
Try this:
public string SaveStringSQL(string pQuery, string ConnectionString)
{
var connection = new Conexao(ConnectionString);
connection.Open();
SqlCommand command = new SqlCommand(pQuery, connection.Connection);
var SavedString = (string)command.ExecuteScalar();
connection.Close();
return SavedString;
}
The ExecuteScalar function saves whatever type of data there is on your database - you just have to specify it.
Keep in mind that it can only save one line at a time.
Related
I am intending to perform a call to ExecuteNonQuery() while the SqlDataReader is opened.
Code:
string commandString = "" //command string
using (SqlDataReader reader = cmd2.ExecuteReader())
{
while (reader.Read())
{
string temp = Convert.ToString(reader["RequestID"]);
string date;
using (SqlCommand cmd3 = new SqlCommand(commandString, con))
{
date = Convert.ToString(cmd3.ExecuteScalar());
}
}
}
I tried executing this but I got the error:
An unhandled exception of type 'System.InvalidOperationException' occurred in System.Data.dll
There is already an open DataReader associated with this Command which must be closed first.
I have the MultipleActiveResultSets set to True in the connection string. May I know if it is possible to do it?
While MARS should work, it's usually not the best choice. Simply load the results of the first query into a DataTable and iterate the rows.
var dt = new DataTable();
using (SqlDataReader reader = cmd2.ExecuteReader())
{
dt.Load(reader);
}
foreach (DataRow row in dt.Rows)
{
string temp = Convert.ToString(row["RequestID"]);
string date;
SqlCommand cmd3 = new SqlCommand(commandString, con)
date = Convert.ToString(cmd3.ExecuteScalar());
}
You need to add MultipleActiveResultSets in your connection string, though you already added. Try below code that's executed successfully,
string conStr = "Data Source=DB_SERVER;Initial Catalog=DB_NAME;User Id=userId; Password=password;MultipleActiveResultSets=True";
using (SqlConnection con = new SqlConnection(conStr)) {
try {
con.Open();
string commandText = #"Select Id from Table1";
string commandText1 = #"Select CreatedDate FROM Table2 Where table1_Id = #table1_Id";
SqlCommand sqlCommand = new SqlCommand(commandText, con);
var dataReader = sqlCommand.ExecuteReader();
string date;
while (dataReader.Read()) {
var vId = dataReader["Id"].ToString();
var sqlCommand1 = new SqlCommand(commandText1, con);
sqlCommand1.Parameters.AddWithValue("#table1_Id", vId);
date= sqlCommand1.ExecuteScalar().ToString();
}
con.Close();
} catch (Exception ex) {
//Handle Exception
}
}
So I've setup my database connection and it does connect.
Now I want to check each row in my table whether the column isactivated is either 0 or 1 because it's a bit but I don't know how to do it.
Would I execute a query? Would I store all the rows in a list and then check?
using (var connection = new SqlConnection(cb.ConnectionString))
{
try
{
connection.Open();
if (connection.State == ConnectionState.Open)
{
Console.WriteLine("Connected!");
}
else
{
Console.WriteLine("Failed..");
}
}
catch (Exception e)
{
Console.WriteLine(e);
throw;
}
}
SqlCommand command = new SqlCommand("SELECT column FROM table", connection);
connection.Open();
SqlDataReader reader = command.ExecuteReader();
while (reader.Read())
{
// 0 = false, 1 = true,
bool result = (bool)reader[0];
//... do whatever you wanna do with the result
}
I think you are looking for something like this:
SqlConnection sqlConnection1 = new SqlConnection("Your Connection String");
SqlCommand cmd = new SqlCommand();
SqlDataReader reader;
cmd.CommandText = "SELECT * FROM Customers";
cmd.CommandType = CommandType.Text;
cmd.Connection = sqlConnection1;
sqlConnection1.Open();
reader = cmd.ExecuteReader();
// Data is accessible through the DataReader object here.
sqlConnection1.Close();
Taken from msdn-lib.
In the SqlDataReader should be all your data including your isactivated column, which you then can check for its respective values.
If you want to read the field you can implement something like this:
using (var connection = new SqlConnection(cb.ConnectionString)) {
try {
connection.Open();
// connection.Open() either succeeds (and so we print the message)
// or throw an exception; no need to check
Console.WriteLine("Connected!");
//TODO: edit the SQL if required
string sql =
#"select IsActivated
from MyTable";
using (var query = new SqlCommand(sql, connection)) {
using (var reader = query.ExecuteReader()) {
while (reader.Read()) {
// Now it's time to answer your question: let's read the value
// reader["IsActivated"] - value of IsActivated as an Object
// Convert.ToBoolean - let .Net do all low level work for you
bool isActivated = Convert.ToBoolean(reader["IsActivated"]);
// Uncomment, if you insist on 0, 1
// int bit = Convert.ToInt32(reader["IsActivated"]);
//TODO: field has been read into isActivated; put relevant code here
}
}
}
}
catch (DataException e) { // Be specific: we know how to process data errors only
Console.WriteLine(e);
throw;
}
}
I've got the following code (here with pseudovalues for readability), where the first connection returns a lot of data (thousands of rows). SqlDataReader reads them one by one by the reader.Read() and then opens a new connection to update each row with new values:
using (SqlConnection conn = new SqlConnection(connString))
using (SqlCommand cmd = new SqlCommand("sp1", conn))
{
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("#param1", param1);
cmd.Connection.Open();
using (SqlDataReader reader = cmd.ExecuteReader())
{
while (reader.Read())
{
try
{
string hash= utils.SHA256.Hashing((string)reader["firstRow"], saltValue);
using (SqlConnection conn2 = new SqlConnection(connString))
using (SqlCommand cmd2 = new SqlCommand("sp2", conn2))
{
cmd2.CommandType = CommandType.StoredProcedure;
cmd2.Parameters.AddWithValue("#param1", param1);
cmd2.Parameters.AddWithValue("#param2", param2);
cmd2.Connection.Open();
cmd2.ExecuteNonQuery();
}
}
catch (SqlException ex)
{
//something
}
}
}
}
but it throws an error:
[InvalidOperationException: Invalid attempt to call Read when reader is closed.]
System.Data.SqlClient.SqlDataReader.ReadInternal(Boolean setTimeout) +640
System.Data.SqlClient.SqlDataReader.Read() +9
In development environment it works fine, but here there's only a few hundred rows. It throws the error immediately, so it doesn't directly look like some kind of timeout, but hey - I don't know...
Don't know why it happens, but it's really a bad idea to execute queries while iterating a live connection to the same database. Keep in mind that as long as you iterate records with a DataReader, the connection is alive.
Much worse is opening then closing a connection thousands of times in a quick succession. This alone can bring any database down to its knees.
Change your logic, store the values you need in a local variable (structure doesn't matter) then use one connection only to execute all the stored procedures you need.
For example:
using (SqlConnection conn = new SqlConnection(connString))
{
conn.Open();
List<string[]> values = new List<string[]>();
using (SqlCommand cmd = new SqlCommand("sp1", conn))
{
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("#param1", param1);
using (SqlDataReader reader = cmd.ExecuteReader())
{
while (reader.Read())
{
try
{
string hash= utils.SHA256.Hashing((string)reader["firstRow"], saltValue);
string anotherValue = (string)reader["secondRow"];
values.Add(new string[] { hash, anotherValue });
}
catch (SqlException ex)
{
//something
}
}
reader.Close();
}
}
if (values.Count > 0)
{
using (SqlCommand cmd2 = new SqlCommand("sp2", conn))
{
cmd2.CommandType = CommandType.StoredProcedure;
cmd2.Parameters.AddWithValue("#param1", null);
cmd2.Parameters.AddWithValue("#param2", null);
values.ForEach(items =>
{
cmd2.Parameters["#param1"].Value = items[0];
cmd2.Parameters["#param2"].Value = items[1];
cmd2.ExecuteNonQuery();
});
}
}
conn.Close();
}
One connection, one command to execute all stored procedures. Really don't need more than that.
I am new to ADO.net. I actually created a sample database and a sample stored procedure. I am very new to this concept. I am not sure of how to make the connection to the database from a C# windows application. Please guide me with some help or sample to do the same.
Something like this... (assuming you'll be passing in a Person object)
public int Insert(Person person)
{
SqlConnection conn = new SqlConnection(connStr);
conn.Open();
SqlCommand dCmd = new SqlCommand("InsertData", conn);
dCmd.CommandType = CommandType.StoredProcedure;
try
{
dCmd.Parameters.AddWithValue("#firstName", person.FirstName);
dCmd.Parameters.AddWithValue("#lastName", person.LastName);
dCmd.Parameters.AddWithValue("#age", person.Age);
return dCmd.ExecuteNonQuery();
}
catch
{
throw;
}
finally
{
dCmd.Dispose();
conn.Close();
conn.Dispose();
}
}
It sounds like you are looking for a tutorial on ADO.NET.
Here is one about straight ADO.NET.
Here is another one about LINQ to SQL.
This is the usual pattern (it might be a bit different for different databases, Sql Server does not require you to specify the parameters in the command text, but Oracle does, and in Oracle, parameters are prefixed with : not with #)
using(var command = yourConnection.CreateCommand())
{
command.CommandText = "YOUR_SP_CALL(#PAR1, #PAR2)";
command.CommandType = CommandType.StoredProcedure;
command.Parameters.Add(new OdbcParameter("#PAR1", "lol"));
command.Parameters.Add(new OdbcParameter("#PAR2", 1337));
command.ExecuteNonQuery();
}
Something like this:
var connectionString = ConfigurationManager.ConnectionStrings["YourConnectionString"].ConnectionString;
var conn = new SqlConnection(connectionString);
var comm = new SqlCommand("YourStoredProc", conn) { CommandType = CommandType.StoredProcedure };
try
{
conn.Open();
// Create variables to match up with session variables
var CloseSchoolID = Session["sessCloseSchoolID"];
// SqlParameter for each parameter in the stored procedure YourStoredProc
var prmClosedDate = new SqlParameter("#prmClosedDate", closedDate);
var prmSchoolID = new SqlParameter("#prmSchoolID", CloseSchoolID);
// Pass the param values to YourStoredProc
comm.Parameters.Add(prmClosedDate);
comm.Parameters.Add(prmSchoolID);
comm.ExecuteNonQuery();
}
catch (SqlException sqlex)
{
}
finally
{
conn.Close();
}
If using SQL Server:
SqlConnection connection = new SqlCOnnection("Data Source=yourserver;Initial Catalog=yourdb;user id=youruser;passowrd=yourpassword");
SqlCommand cmd = new SqlCommand("StoredProcName", connection);
cmd.CommandType=StoredProcedureType.Command;
connection.Open();
cmd.ExecuteNonQuery();
connection.Close();
If not then replace Sql with Ole and change the connection string.
Here is a good starting point http://support.microsoft.com/kb/310130
OdbcConnection cn;
OdbcCommand cmd;
OdbcParameter prm;
OdbcDataReader dr;
try {
//Change the connection string to use your SQL Server.
cn = new OdbcConnection("Driver={SQL Server};Server=servername;Database=Northwind;Trusted_Connection=Yes");
//Use ODBC call syntax.
cmd = new OdbcCommand("{call CustOrderHist (?)}", cn);
prm = cmd.Parameters.Add("#CustomerID", OdbcType.Char, 5);
prm.Value = "ALFKI";
cn.Open();
dr = cmd.ExecuteReader();
//List each product.
while (dr.Read())
Console.WriteLine(dr.GetString(0));
//Clean up.
dr.Close();
cn.Close();
}
catch (OdbcException o) {
MessageBox.Show(o.Message.ToString());
}
This is a really, really stupid question but I am so accustomed to using linq / other methods for connecting and querying a database that I never stopped to learn how to do it from the ground up.
Question: How do I establish a manual connection to a database and pass it a string param in C#? (yes, I know.. pure ignorance).
Thanks
using (SqlConnection conn = new SqlConnection(databaseConnectionString))
{
using (SqlCommand cmd = conn.CreateCommand())
{
cmd.CommandText = "StoredProcedureName";
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("#ID", fileID);
conn.Open();
using (SqlDataReader rdr =
cmd.ExecuteReader(CommandBehavior.CloseConnection))
{
if (rdr.Read())
{
// process row from resultset;
}
}
}
}
One uses the SqlCommand class to execute commands (either stored procedures or sql) on SQL Server using ado.net. Tutorials abound.
Here's an example from http://www.csharp-station.com/Tutorials/AdoDotNet/Lesson07.aspx
public void RunStoredProcParams()
{
SqlConnection conn = null;
SqlDataReader rdr = null;
// typically obtained from user
// input, but we take a short cut
string custId = "FURIB";
Console.WriteLine("\nCustomer Order History:\n");
try
{
// create and open a connection object
conn = new
SqlConnection("Server=(local);DataBase=Northwind;Integrated Security=SSPI");
conn.Open();
// 1. create a command object identifying
// the stored procedure
SqlCommand cmd = new SqlCommand(
"CustOrderHist", conn);
// 2. set the command object so it knows
// to execute a stored procedure
cmd.CommandType = CommandType.StoredProcedure;
// 3. add parameter to command, which
// will be passed to the stored procedure
cmd.Parameters.Add(
new SqlParameter("#CustomerID", custId));
// execute the command
rdr = cmd.ExecuteReader();
// iterate through results, printing each to console
while (rdr.Read())
{
Console.WriteLine(
"Product: {0,-35} Total: {1,2}",
rdr["ProductName"],
rdr["Total"]);
}
}
finally
{
if (conn != null)
{
conn.Close();
}
if (rdr != null)
{
rdr.Close();
}
}
}
3 things no one else has shown you yet:
"Stacking" using statements
Setting an explicit parameter type rather than letting .Net try to pick one for you
"var" keyword
.
string sql = "MyProcedureName";
using (var cn = new SqlConnection(databaseConnectionString))
using (var cmd = new SqlCommand(sql, cn))
{
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add("#ParameterName", SqlDbType.VarChar, 50)
.Value = "MyParameterValue";
conn.Open();
using (SqlDataReader rdr =
cmd.ExecuteReader(CommandBehavior.CloseConnection))
{
if (rdr.Read())
{
// process row from resultset;
}
}
}