I am using ASP.Net WebserviceApplication for my application and it is communicating with my SQL Server. Should I close SQLConnection after all user's sql transactions or it should be open everytime?
For example;
public void Connection()
{
if (connection == null)
connection = new SqlConnection(ConfigurationManager.ConnectionStrings["Conn"].ToString());
if (connection.State == ConnectionState.Closed)
connection.Open();
else if (connection.State == ConnectionState.Broken)
{
connection.Close();
connection.Open();
}
}
[WebMethod]
public long GetUsersRankMonthly(string userName)
{
Connection();
SqlCommand command = new SqlCommand("Select scores.Rank From (SELECT ROW_NUMBER() OVER(ORDER BY Score DESC) AS Rank,Score,NickName,ID FROM teatalay.TopScoresGeneral) scores Where UserName = #userName", connection);
command.Parameters.Add(new SqlParameter("#userName", userName));
var result = (long?)command.ExecuteScalar();
return result.HasValue ? result.Value : -1;
}
Thank you.
Wrap your transactions in a using statement when using a sql command. Let ASP.NET take care of SQL Connection pooling. It is a bit more refined at it than your code. Keep everything as condensed as possible and only modify if you notice that the number of connections to your server are what are the source of your performance issues.
Edit
using (var cnn = new SqlConnection("connection string here")){
using (var cmd = new SqlCommand("SProc or parametized text", cnn)){
cnn.Open();
// do stuff
cnn.Close();
}
}
In general when handling connections is better to use using moreover the block
if (connection.State == ConnectionState.Closed)
doesn't guarranty that it will open you the connection because you might be at ConnectionState.Connecting
The using statement guarantes it will close you connection when finished:
public long GetUsersRankMonthly(string userName)
{
connection = new SqlConnection(ConfigurationManager.ConnectionStrings["Conn"].ToString());
using (connenction)
{
connenction.Open();
SqlCommand command = new SqlCommand("Select scores.Rank From (SELECT ROW_NUMBER() OVER(ORDER BY Score DESC) AS Rank,Score,NickName,ID FROM teatalay.TopScoresGeneral) scores Where UserName = #userName", connection);
using (command)
{
..........
......
}
}
}
Related
I need to use a variable (edifcodigo) which assigned value is retrieved from one query to insert it in a table by using other query but there is a error that says this variable is not available in actual context. I'm kind of new in aspnet, could anybody know how to figure this out?
This is the code I have:
//Connect to db
string connetionString = #"myconexionstring";
string sql = "SELECT TOP 1 id_proyecto AS codigo FROM DNN_SCO_PROY_CO_PROYECTO_TBL WHERE nombre_proyecto= '"+ uedif +"'";
//find building code by querying the database
try
{
using (SqlConnection conexion = new SqlConnection(connetionString))
{
conexion.Open();
using (SqlCommand query = new SqlCommand(sql, conexion))
{
SqlDataReader result = query.ExecuteReader();
while (result.Read())
{
string edifcodigo = result["codigo"].ToString();
}
}
}
}
catch (Exception ex)
{
Response.Write(ex.Message);
}
//Save referer friend
try
{
using (SqlConnection conn = new SqlConnection(connetionString))
{
conn.Open();
using (SqlCommand cmd = new SqlCommand("DNN_SVI_SCO_DATOS_RECOMIENDA_AMIGO_SP", conn))
{
cmd.CommandType = System.Data.CommandType.StoredProcedure;
cmd.Parameters.Add("#DRA_PROYECTO_CLIENTE", System.Data.SqlDbType.VarChar).Value = edifcodigo; ;
}
}
}
catch (Exception ex)
{
Response.Write(ex.Message);
}
That's because you declared the variable inside a different code block. Every time you open a curly bracket, you open a new code block. Every time you close the curly bracket, you close the current code block. Each code block have it's own scope - it can access variables declared in the surrounding code block, but not variables declared in "sibling" code blocks.
Also, please read about parameterized queries and how they protect you from SQL injection, and change your queries accordingly.
Also, you don't need to close the connection between the two commands, and you can reuse a single command instance in this case. Here is an improved version of your code:
//Connect to db
var connetionString = #"myconexionstring";
var sql = "SELECT TOP 1 id_proyecto AS codigo FROM DNN_SCO_PROY_CO_PROYECTO_TBL WHERE nombre_proyecto = #nombre_proyecto";
//find building code by querying the database
try
{
using (var conexion = new SqlConnection(connetionString))
{
conexion.Open();
using (var cmd = new SqlCommand(sql, conexion))
{
cmd.Parameters.Add("#nombre_proyecto", SqlDbType.NVarChar).Value = uedif;
var edifcodigo = cmd.ExecuteScalar();
//Save referer friend
cmd.Parameters.Clear();
cmd.CommandText = "DNN_SVI_SCO_DATOS_RECOMIENDA_AMIGO_SP";
cmd.CommandType = System.Data.CommandType.StoredProcedure;
cmd.Parameters.Add("#DRA_PROYECTO_CLIENTE", System.Data.SqlDbType.VarChar).Value = edifcodigo; ;
}
}
}
catch (Exception ex)
{
Response.Write(ex.Message);
}
You are declaring the string variable inside your while loop, it loses scope once you exit the while loop, move it's declaration above with:
string connetionString = #"myconexionstring";
string sql = "SELECT TOP 1 id_proyecto AS codigo FROM DNN_SCO_PROY_CO_PROYECTO_TBL WHERE nombre_proyecto= '"+ uedif +"'";
string edifcodigo = "";
You are trying to use a variable that declared in another scope. edifcodigo should be declared in the parent scope of both try blocks.
//Connect to db
string connetionString = #"myconexionstring";
string sql = "SELECT TOP 1 id_proyecto AS codigo FROM DNN_SCO_PROY_CO_PROYECTO_TBL WHERE nombre_proyecto= '"+ uedif +"'";
string edifcodigo=""; // YOU SHOULD DECLARE edifcodigo HERE
and than rest of code will come
//find building code by querying the database
try
{
using (SqlConnection conexion = new SqlConnection(connetionString))
{
conexion.Open();
using (SqlCommand query = new SqlCommand(sql, conexion))
{
SqlDataReader result = query.ExecuteReader();
while (result.Read())
{
edifcodigo = result["codigo"].ToString();
}
}
}
}
catch (Exception ex)
{
Response.Write(ex.Message);
}
//Save referrer friend
try
{
using (SqlConnection conn = new SqlConnection(connetionString))
{
conn.Open();
using (SqlCommand cmd = new SqlCommand("DNN_SVI_SCO_DATOS_RECOMIENDA_AMIGO_SP", conn))
{
cmd.CommandType = System.Data.CommandType.StoredProcedure;
cmd.Parameters.Add("#DRA_PROYECTO_CLIENTE", System.Data.SqlDbType.VarChar).Value = edifcodigo; ;
}
}
}
catch (Exception ex)
{
Response.Write(ex.Message);
}
I am having trouble connecting to my database to run a query. Here us the connection and query info:
string connectionString = "Data Source=(LocalDB)\v11.0;AttachDbFilename=c:\\Webs\\MvcFFL\\MvcFFL\\App_Data\\Players.mdf;Integrated Security=True";
string queryString = "Truncate table Players;";
using (SqlConnection connection = new SqlConnection(connectionString))
{
SqlCommand command = new SqlCommand(queryString, connection);
connection.Open(); <- Fails here opening the connection
SqlDataReader reader = command.ExecuteReader();
try
{
while (reader.Read())
{
Console.WriteLine(String.Format("{0}, {1}",
reader[0], reader[1]));
}
}
finally
{
// Always call Close when done reading.
reader.Close();
}
}
Can someone explain why this is failing to open the connection. This is using SQL Server. I have this declared at the top:
using System.Data.SqlClient;
I am having problem when doing retrieve function in 3-tier in C#. Here is the codes:
public DistributionStandardPackingUnits getSPUDetail(string distributionID)
{
DistributionStandardPackingUnits SPUFound = new DistributionStandardPackingUnits();
using (var connection = new SqlConnection(FoodBankDB.connectionString))
{
SqlCommand command = new SqlCommand("SELECT name, description, quantity FROM dbo.DistributionStandardPackingUnits WHERE distribution = '" + distributionID + "'", connection);
connection.Open();
using (var dr = command.ExecuteReader())
{
while (dr.Read())
{
string name = dr["name"].ToString();
string description = dr["description"].ToString();
string quantity = dr["quantity"].ToString();
SPUFound = new DistributionStandardPackingUnits(name, description, quantity);
}
}
}
return SPUFound;
}
When I run in browser, it just won't show up any retrieved data. When I run in debugging mode, I realized that when it hits the while loop, instead of executing the dr.Read(), it simply just skip the entire while loop and return null values. I wonder what problem has caused this. I tested my query using the test query, it returns me something that I wanted so I think the problem does not lies at the Sql statement.
Thanks in advance.
Edited Portion
public static SqlDataReader executeReader(string query)
{
SqlDataReader result = null;
System.Diagnostics.Debug.WriteLine("FoodBankDB executeReader: " + query);
SqlConnection connection = new SqlConnection(connectionString);
SqlCommand command = new SqlCommand(query, connection);
connection.Open();
result = command.ExecuteReader();
connection.Close();
return result;
}
I have a database in which a table has name Registration which is used to register the user.
It has only two column one is Username and one is password.
A page named Register.aspx is used for registering the member which have two textbox one is for taking Username(textbox1) and one is for taking password(textbox2) and one button for insert these value in database.
The Main problem is that we cannot write statement like this :
Insert into Registration (Username, password)
values ('TextBox1.text','TextBox2.text')
I am using ADO.net Connection oriented mode, I googled but I didn't find any way to insert row in SQL database in connected mode. Please provide me a idea for inserting this row?
ADO.NET has DataReader which supports Connected mode. All else are disconnected.
DataReader is connected architecture since it keeps conneection open untill all records are fetched
If you want to insert in ADO.NET then you should perform the following steps:
private void btnadd_Click(object sender, EventArgs e)
{
try
{
//create object of Connection Class..................
SqlConnection con = new SqlConnection();
// Set Connection String property of Connection object..................
con.ConnectionString = "Data Source=KUSH-PC;Initial Catalog=test;Integrated Security=True";
// Open Connection..................
con.Open();
//Create object of Command Class................
SqlCommand cmd = new SqlCommand();
//set Connection Property of Command object.............
cmd.Connection = con;
//Set Command type of command object
//1.StoredProcedure
//2.TableDirect
//3.Text (By Default)
cmd.CommandType = CommandType.Text;
//Set Command text Property of command object.........
cmd.CommandText = "Insert into Registration (Username, password) values ('#user','#pass')";
//Assign values as `parameter`. It avoids `SQL Injection`
cmd.Parameters.AddWithValue("user", TextBox1.text);
cmd.Parameters.AddWithValue("pass", TextBox2.text);
Execute command by calling following method................
1.ExecuteNonQuery()
This is used for insert,delete,update command...........
2.ExecuteScalar()
This returns a single value .........(used only for select command)
3.ExecuteReader()
Return one or more than one record.
cmd.ExecuteNonQuery();
con.Close();
MessageBox.Show("Data Saved");
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
con.Close();
}
}
try
{
using (var connection = new SqlConnection(yourConnectionString))
{
string queryString = "Select id, name, age from Table where name = #name";
using (var command = new SqlCommand(queryString, Connection))
{
command.Parameters.AddWithValue("#name", name);
Connection.Open();
SqlDataReader dataReader = command.ExecuteReader();
while (dataReader.Read())
{
item = new Item(long.Parse(dataReader[0].ToString()),
dataReader[1].ToString(),
int.Parse(dataReader[2].ToString()));
}
dataReader.Close();
}
}
}
catch (Exception ex)
{
// if exception will happen in constructor of SqlConnection or Command, the // resource can leak but Dispose method will never be called, couse the object was not created yet.
// Trace and handle here
throw;
}
finally
{
}
But ADO.net is useless for enterprice development. You have to have and abstraction from Data Acess Layer and go to entities, not table records
Use the ORM, Luke!
using System.Data.SqlClient;
string cnstr = "server=.;database=dbname;user=username;password=password;";
SqlConnection con = new SqlConnection(cnstr);
SqlCommand cmd = new SqlCommand { Connection = con };
cmd.CommandText = "Insert into Registration (Username, password) values ('#user','#pass')";
cmd.Parameters.AddWithValue("user", TextBox1.text);
cmd.Parameters.AddWithValue("pass", TextBox2.text);
try
{
con.Open();
cmd.ExecuteNonQuery();
}
catch (Exception)
{
//something;
}
finally
{
if (con != null)
con.Close();
}
I access data in .dbf files via System.Data.OleDb (vfpoledb.dll). How can I find out whether table exists via SQL command? Something similar to the following on SQL server:
IF (EXISTS (SELECT * FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = 'TheTable'))
BEGIN
--Do Stuff
END
If you have a dbc file you can query it to see if the table exists.
string dbc = "northwind.dbc";
using (OleDbConnection conn = new OleDbConnection(connectionString)) {
DataTable dt = new DataTable();
string sql = string.Format(#"SELECT * FROM {0} WHERE ALLTRIM(ObjectType) = 'Table' AND UPPER(ALLTRIM(ObjectName)) = '{1}'", dbc, tableName.ToUpper());
OleDbDataAdapter da = new OleDbDataAdapter(sql, conn);
da.Fill(dt);
bool tableExists = dt != null && dt.Rows.Count == 1;
}
But really you don't need a sql command or a dbc file to get that information. You can get it straight from the OleDbConnection using the GetSchema method.
using (OleDbConnection conn = new OleDbConnection(connectionString)) {
conn.Open();
DataTable tables = conn.GetSchema("Tables");
conn.Close();
var tableExists = (from row in tables.AsEnumerable()
where row.Field<string>("Table_Name").Equals(tableName, StringComparison.CurrentCultureIgnoreCase)
select row.Field<string>("Table_Name")).FirstOrDefault() != null;
}
Additionally, if you are connecting to DBF tables that are "FREE" tables and NOT actually part of a connected "database" (.dbc), then you can just check for the file's existence or not... Such as in C# via
if( File.Exists( PathToTheDatabaseDirectory + TableYouExpect + ".DBF" ))
file is there
else
file is missing
I don't know how to do it only using SQL but maybe you could check for the existence of the file on disk using the File.Exists Method or you could write some code to check for the existence of the dbf using the OleDb classes:
private bool DbfExists(string dbfName, string connectionString)
{
bool dbfExists = true;
using(OleDbConnection conn = new OleDbConnection(connectionString))
{
string sql = string.Format("SELECT * FROM {0}", dbfName);
using(OleDbCommand command = new OleDbCommand(sql, conn))
{
OleDbDataReader reader = null;
try
{
conn.Open();
reader = command.ExecuteReader();
}
catch(Exception ex)
{
dbfExists = false;
}
finally
{
conn.Close();
reader = null;
}
}
}
return dbfExists;
}
I have not tried compiling this code so it may need to be tweaked a bit.