I am querying a Microsoft SQL Database using the SqlConnection, SqlCommand and SqlReader, much like described in https://learn.microsoft.com/en-us/dotnet/framework/data/adonet/retrieving-data-using-a-datareader
Now, an SqlCommand allows to set the CommandTimeout, and I am doing it like so (simplified):
using (SqlConnection connection = GetConnection()) {
connection.Open();
using (SqlCommand command = connection.CreateCommand()) {
command.CommandText = query; //My custom SQL query
command.CommandType = CommandType.Text;
//Set Timeout
command.CommandTimeout = timeout.Value; //My custom timeout
using (SqlDataReader reader = command.ExecuteReader()) {
while (reader.Read()) {
//Read row by row and do stuff
}
}
}
}
My question is, to what does the Timeout actually apply to? Is it
The time spent in ExecuteReader()
The time spent in Read()
both of those
something else?
There seems no documentation of this specifically, neither in MSDN nor on the web.
It will apply to the time executing the command against the database which is command.ExecuteReader() which is complete by the time you start reading the records. You could test that by putting a break point in after that on the while and and sitting there - you won't hit your timeout.
Related
So I have this Azure function that works, and an Azure SQL DB with some data. But I cannot find a decent example to get data from the DB into the function. Surely, crafting a query string and SQLCommand.BeginExecuteReader/EndExecuteReader is not the preferred way, right?
LINQtoSQL perhaps?
Thanks, Bezz
You are free to use any .NET Data Access library that's available for other types of applications: ADO.NET, Entity Framework, Dapper etc.
A simple example:
Use Azure Functions to connect to an Azure SQL Database.
Apparently, it was quite simple. This code did the trick. Although I'm not completely happy with the fact that I'm crafting a query string. For now, it will do.
#r "System.Configuration"
#r "System.Data"
using System.Configuration;
using System.Data.SqlClient;
using System.Threading.Tasks;
using System.Net;
public static async Task<HttpResponseMessage> Run(HttpRequestMessage req, TraceWriter log)
{
var str = ConfigurationManager.ConnectionStrings["sqldb_connection"].ConnectionString;
var caterers = new List<string>();
using (SqlConnection conn = new SqlConnection(str))
{
conn.Open();
SqlCommand cmd = new SqlCommand();
SqlDataReader reader;
cmd.CommandText = "SELECT * FROM Caterers";
cmd.Connection = conn;
reader = cmd.ExecuteReader();
if (reader.HasRows)
{
while (reader.Read())
{
caterers.Add(reader.GetString(1));
}
}
conn.Close();
}
return req.CreateResponse(HttpStatusCode.OK, caterers);
}
I'm trying to make a simple program that has a log-in part, with a local database just for testing.And i keep getting an error when I try to open the connection to the SQL database.
private void logInButton_Click(object sender, EventArgs e)
{
MainMenu openMainMenu = new MainMenu();
SqlConnection sqlcon = new SqlConnection(#"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=C: \Users\Nea Florin\Desktop\PlatformaTestare\PlatformaTestare\Server.mdf;Integrated Security=True;Connect Timeout=30");
sqlcon.Open();
SqlCommand cmd = new SqlCommand("Select * from Table Where username ='" + usernameTextBox.Text + "' and password = '" + passwrodTextBox.Text + "'");
SqlDataAdapter sda = new SqlDataAdapter(cmd);
DataTable dtbl = new DataTable();
sda.Fill(dtbl);
if (dtbl.Rows.Count > 0)
{
openMainMenu.Show();
this.Hide();
}
else
MessageBox.Show("Wrong username or password!");
}
I get the error at sqlcon.Open();, and it is: "An unhandled exception of type 'System.Data.SqlClient.SqlException' occurred in System.Data.dll
Additional information: An attempt to attach an auto-named database for file C: \Users\Nea Florin\Desktop\PlatformaTestare\PlatformaTestare\Server.mdf failed. A database with the same name exists, or specified file cannot be opened, or it is located on UNC share."
Well, the best advice I can give you is to google the error message. Keep in mind that if there is an error message it means that the problem is well known an as such it's a safe bet that someone have encountered it before you and managed to solve it. The first 4 results of this search are on stackoverflow and at least two of them have accepted answers, so I believe a little reasearch would have saved you a long time.
This is the best advice because it streaches far beyond your current problem. I firmly believe that good searching skills is the most important and most powerfull tools of a sotfware developer. I can assure you, no matter how much time you are developing software, almost every exception you get, someone else have already solved and posted the solution somewhere, you only need to find it.
Now, as for the code it self - You have some major problems other then the exception you are asking about:
Concatenating strings into sql statements instead of using parameters expose your code to SQL injection attacks. This is a very serious threat that is extremely easy to fix.
Using insntances of classes that implements the IDisposable interface without properly disposing them may lead to memory leak. Read about the using statement and make it a habit to use it every time it's possible.
Exception handling. Currently, if your database can't be reached, you get an exception and your program crash. You should use a try...catch block anywhere you can't control in code to let your program end gracefuly instead. (Don't ever use try...catch for things you can do in code such as validate user input or checking division by zero - only for things that are beyon your control such as database availability.)
Having said all that, your code should look something like this:
private void logInButton_Click(object sender, EventArgs e)
{
using (var sqlcon = new SqlConnection(#"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|C:\Users\Nea Florin\Desktop\PlatformaTestare\PlatformaTestare\Server.mdf;Integrated Security=True;Connect Timeout=30"))
{
sqlcon.Open();
using (var cmd = new SqlCommand("Select 1 from Table Where username = #userName and password = #password"))
{
cmd.Parameters.Add("#userName", SqlDbType.NVarChar).Value = usernameTextBox.Text;
cmd.Parameters.Add("#password", SqlDbType.NVarChar).Value = passwrodTextBox.Text;
using (var dtbl = new DataTable())
{
using (var sda = new SqlDataAdapter(cmd))
{
sda.Fill(dtbl);
}
if (dtbl.Rows.Count > 0)
{
var openMainMenu = new MainMenu();
openMainMenu.Show();
this.Hide();
}
}
else
{
MessageBox.Show("Wrong username or password!");
}
}
}
I'm executing same command in every 2 seconds. I think following code creates multiple connections:
[System.Web.Services.WebMethod]
public static int getActivity()
{
using (SqlConnection connection = new SqlConnection(ConfigurationManager.ConnectionStrings["dbconnection"].ToString()))
{
connection.Open();
using (var cmd = new SqlCommand("SELECT TOP 1 ValueX FROM TABLE WHERE ID= 2 AND EVENTID = 2 ORDER BY DATE DESC", connection))
{
var x = cmd.ExecuteScalar();
int Result;
if (x != null)
{
Result = int.Parse(x.ToString());
Console.WriteLine("USER ACTIVITY : " + Result);
}
else
{
Result = -999;
}
connection.Close();
return Result;
}
}
}
If I call this method several time Does following code make multi connection Or single connection ?
using (SqlConnection connection = new SqlConnection(ConfigurationManager.ConnectionStrings["dbconnection"].ToString()))
Can someone explain whether I need to modify this code or Is this good one ?
Thanks.
Since you are using the using statement clause so once you are done with the method the resources are freed and the connection is closed. So everytime when you call the same method a new connection will be made. When you are using the using clause then it is equivalent to the below code:
SqlConnection connection = null;
try
{
connection = new SqlConnection(connectionString);
}
finally
{
if(connection != null)
((IDisposable)connection).Dispose();
}
Also note that you dont need to explicitly call the connection.Close(); in your method as using statement will take care of it.
Your method is fine, you just don't need connection.Close() as described by Rahul. Using statement when dealing with SQL objects is good practice.
What you should keep in mind, is that ADO.NET connection pooling, takes care of handling new objects referring to the same connection string, thus minimizing the time needed to open a connection.
More about connection pooling can be found Here
I have problem with connecting to firebird tables. I tried every connection string i could find on internet but it doesn't work. Problem comes when i open connection
Here is code
private void RutinskiPopis_Load(object sender, EventArgs e)
{
SqlConnection con = new SqlConnection(#"User ID=sysdba;Password=masterkey;Database=localhost:D:\\TDWORK.FDB;Data Source=localhost;");
SqlCommand cmd = new SqlCommand("SELECT Opis, Broj FROM PLNAZIVI", con);
con.Open();
SqlDataReader dr = cmd.ExecuteReader();
while (dr.Read())
{
comboBox1_Data((IDataRecord)dr);
}
con.Close();
}
Can anyone help me with that connection string?
Here is full connection string
initial catalog=D:\TDWORK.FDB;data source=localhost;user id=SYSDBA;role=admin
The problem is that you are using SqlConnection, which can only connect to Microsoft SQL Server. For Firebird you need to use FbConnection.
See for examples: .NET - examples of use.
I solved this by using FbConnection instead of SqlConnection, and then using standard firebird connection string.
I'm looking for some examples on how to best use SqlDataAdapter to access and update data in my application.
Right now I have something like this:
SqlDataAdapter adapter;
DataSet myData = MyDataAccessClass.GetData("Select * from Students", ref adapter);
// change some data here and save changes
adapter.Update();
All of this occurs in code behind, and I dont really like it at all.
So, I'm trying to find a way to do something like this:
DataSet myData = MyDataAccessClass.GetStudents();
// change some data and save changes
MyDataAccessClass.SaveStudents(myData);
Where SaveStudents method still uses SqlDataAdapter to update db.
Any ideas on how to make this work or some pointers to best practices of doing
something like this are highly appreciated. Thank you.
That seems like a fairly basic Data Access Layer implementation, to me. Generally, I do it something like this:
public class MyDataAccessClass
{
private string ConnString;
public MyDataAccessClass()
{ //Get connection string from configuration file }
public MyDataAccessClass(string connString)
{ ConnString = connString; }
public DataSet GetAllStudents()
{
//your SQL Adapter code here...
}
}
One note that I'd make is that with so many ORM solutions (including just Entity Framework and Linq2Sql) available, you may want to consider using collections of objects instead of data-sets for your Data Representations. Then you can have a method like:
public void CreateUpdateStudent(Student student)
{
//update database
}
That's fairly subjective, I'll admit, but I find it preferable to using straight DataSets.
If you want to get update data using the sql-data-adapter then you could use these
Using System.Data.SqlClient;
SqlConnection con = new SqlConnection("Data Source=abcd-pc;Initial Catalog=user_info;Integrated Security=True");
SqlDataAdapter da = new SqlDataAdapter();
try
{
da.UpdateCommand = new SqlCommand("Update logindemo set password=#pswd where username=#uname",con);
da.UpdateCommand.Parameters.Add("#pswd", SqlDbType.VarChar).Value = txtpass.Text;
da.UpdateCommand.Parameters.Add("#uname", SqlDbType.VarChar).Value = txtusername.Text;
con.Open();
da.UpdateCommand.ExecuteNonQuery();
Label1.Text = "Data Updated";
con.Close();
}
catch
{
Label1.Text = "Unable To Connect";
}
I hope you understand how to update the data easily. It just like the example. You can use these type of example in Inserting into the Data, and Deleting the Data with using specific the command and sql query as it required.