I am trying to connect to the SQL server database, but it throws an error. Here is the code I have tried :

Question

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An exception of type 'System.Data.SqlClient.SqlException' occurred in System.Data.dll but was not handled in user code
i am stuck here, con.Open();

What I have tried:

C#

SqlConnection con = new SqlConnection("Data Source=DESKTOP-72CIIS5;Initial Catalog=user_desk;User ID=sa;Password=***********");
SqlCommand cmd = new SqlCommand("insert into usertable values ('" + textBox1.Text + "','" + textBox2.Text + "','" + textBox3.Text + "','" + textBox4.Text + "',)", con);
con.Open();

Posted 6-Nov-18 1:25am

ali walo

Updated 7-Nov-18 21:18pm

v2

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Comments

F-ES Sitecore 6-Nov-18 7:31am

Your connection string is wrong. If you look at the actual exception message it will give you hint about what is wrong.

2 solutions

Solution 1

Don't do it like that! Never concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Always use Parameterized queries instead.

When you concatenate strings, you cause problems because SQL receives commands like:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'Baker's Wood'

The quote the user added terminates the string as far as SQL is concerned and you get problems. But it could be worse. If I come along and type this instead: "x';DROP TABLE MyTable;--" Then SQL receives a very different command:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'x';DROP TABLE MyTable;--'

Which SQL sees as three separate commands:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'x';

A perfectly valid SELECT

SQL

DROP TABLE MyTable;

A perfectly valid "delete the table" command

SQL

--'

And everything else is a comment.
So it does: selects any matching rows, deletes the table from the DB, and ignores anything else.

So ALWAYS use parameterized queries! Or be prepared to restore your DB from backup frequently. You do take backups regularly, don't you?

And if you fix that, the syntax problem with your SQL will be very, very obvious:

C#

using (SqlCommand cmd = new SqlCommand("INSERT INTO usertable VALUES (@P1, @P2, @P3, @P4, @p5,)", con)
   {
   ...

In addition:
1) Always list the columns you wish to insert into. That way, changes to your table (and IDENTITY columns) don;t mess up your data.
2) Do yourself a favour, and stop using Visual Studio default names for everything - you may remember that "TextBox8" is the mobile number today, but when you have to modify it in three weeks time, will you then? Use descriptive names - "tbMobileNo" for example - and your code becomes easier to read, more self documenting, easier to maintain - and surprisingly quicker to code because Intellisense can get to to "tbMobile" in three keystrokes, where "TextBox8" takes thinking about and 8 keystrokes...

Posted 6-Nov-18 1:33am

OriginalGriff

Comments

Richard Deeming 6-Nov-18 9:01am

Also, connecting as sa is particularly dangerous. 🤦‍♂️

ali walo 7-Nov-18 4:16am

so how I fix it plz tell me?

OriginalGriff 7-Nov-18 4:28am

Use parameterised queries! Google will show you how ...

OriginalGriff 7-Nov-18 4:30am

And check your connection string (they shouldn't be hard coded either). This may help:
https://www.codeproject.com/Tips/1198443/Simple-SQL-Connection-String-Creation

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M.Kamran Asim · Accepted Answer · 2018-11-07T21:18:00

It seems you are opening connection in wrong place.

steps to follow

1. Create Sql Connection
2. Open connection
3. assign connection to command.

while in your case your are swaping 2 and 3.

More over use parameters instead of building query

here is example for you

C#

using (connection = new SqlConnection(connectionString))
{
  connection.Open();
  var command = new SqlCommand();
  command.CommandText = @"
     INSERT INTO [dbo].[Product]
           ([ProductId]
           ,[Name]
           ,[Description])           
     VALUES
          (@Pid,
           @Name,
           @Desc)";
 command.Connection = connection;
 command.Parameters.Add(new SqlParameter("@Pid", SqlDbType.VarChar, 100)).Value = product.ProductId;
 command.Parameters.Add(new SqlParameter("@Name", SqlDbType.VarChar, 100)).Value = product.Name;
 command.Parameters.Add(new SqlParameter("@Desc", SqlDbType.VarChar, 255)).Value = product.Description;                
 command.ExecuteNonQuery();
}