将文本框值与数据库进行比较

Question

HI ! I would like to compare values from a textbox with data from a table. I tried this code but i got the error that the input string was in the wrong format! code:

string connectionString = 
    "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=save.mdb";

try
{

   database = new OleDbConnection(connectionString);
   database.Open();
   string queryString = "SELECT zivila.naziv,users.user_name FROM (obroki_save "
       + " LEFT JOIN zivila ON zivila.ID=obroki_save.ID_zivila) "
       + " LEFT JOIN users ON users.ID=obroki_save.ID_uporabnika "
       + " WHERE users.ID='" +Convert.ToInt16(id.iDTextBox.Text)+"'"; 
   loadDataGrid(queryString);
}
catch (Exception ex)
{
   MessageBox.Show(ex.Message);
   return;
}

Answer 1

your connectionstring should look like this:

Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\\mydatabase.mdb;User Id=admin;Password=;

Further information on connectionstrings you can find on connectionstrings.com

Answer 2

when building your sql, you're trying to concatenate a string and an Int16 value. try removing the Convert.ToInt16(), leaving just the string value of the textbox.

Answer 3

Try changing your last line to

+ " WHERE users.ID=" +Convert.ToInt16(id.iDTextBox.Text);

basically removing the single quotes from around the Int16

Answer 4

You could try this:

string connectionString = 
    "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=save.mdb";

try
{
       Int16 id = Int16.Parse(id.iDTextBox.Text);

   database = new OleDbConnection(connectionString);
   database.Open();
   string queryString = "SELECT zivila.naziv,users.user_name FROM (obroki_save "
       + " LEFT JOIN zivila ON zivila.ID=obroki_save.ID_zivila) "
       + " LEFT JOIN users ON users.ID=obroki_save.ID_uporabnika "
       + " WHERE users.ID=" + id.ToString(); 
   loadDataGrid(queryString);
       database.Close();
}
catch (FormatException fex)
{
   MessageBox.Show(fex.Message);
   return;
}
catch (Exception ex)
{
   MessageBox.Show(ex.Message);
   return;
}

This way you would intercept bad data and protect yourself from Sql Injection.

Also, don't forget to Close your connection, or read up on the using the using keyword .

Also try to run the query with a hardcoded id value in your sql editor to make sure it works:

SELECT zivila.naziv,users.user_name 
FROM (obroki_save AS os LEFT JOIN zivila AS z ON z.ID=os.ID_zivila) 
LEFT JOIN users ON users.ID=obroki_save.ID_uporabnika 
WHERE users.ID=16

Answer 5

if your ID field is an int, you shouldn't be putting ' around it.

so change

 + " WHERE users.ID='" +Convert.ToInt16(id.iDTextBox.Text)+"'"; 

to

 + " WHERE users.ID=" +Convert.ToInt16(id.iDTextBox.Text);