How to solve this error of conversion failed? - sql

Question

I am getting this error
Conversion failed when converting the varchar value 'Thowheed' to data type int.
I visited and checked in stack overflow, but I couldn't find answer
I added values in drop down list, once I select and click ok button it has to show me the record from database.
This is my code
string cs = ConfigurationManager.ConnectionStrings["Nibrass_DBConnectionString"].ConnectionString;
using (SqlConnection con = new SqlConnection(cs))
{
SqlCommand cmd = new SqlCommand();
cmd.Connection = con;
cmd.CommandText = "SELECT Date as Date,Credit, Debit_From as Received_From, Credit_Amount as amount, Reason From Transaction_Credit where Credit = " + DropDownListSelectAccount.SelectedValue+ " or cast(Debit_From as varchar) = " + DropDownListSelectAccount.SelectedValue + " ORDER BY Date DESC";
con.Open();
SqlDataReader rd = cmd.ExecuteReader();
while(rd.Read())
{
DateTime dt = Convert.ToDateTime(rd[0]);
string receivedFrom = rd[1].ToString();
int amount = Convert.ToInt32(rd[2]);
}
con.Close();
}
My database table definition is
CREATE TABLE [dbo].[Transaction_Credit]
(
[Date] DATE NOT NULL,
[Credit] VARCHAR (50) NOT NULL,
[Debit_From] VARCHAR (50) NOT NULL,
[Reason] VARCHAR (100) NULL,
[Credit_Amount] INT NOT NULL,
[Balance] INT NULL
);

Answer 1

You should not be concatenating your string. This is a bad practice and your code becomes vulnerable to SQL Injection.
You should use parameters instead:
cmd.CommandText = #"
SELECT Date
, Credit
, Debit_From AS Received_From
, Credit_Amount AS Amount
, Reason
FROM Transaction_Credit
WHERE Credit = #DropDownListSelectAccount
OR Debit_From = #DropDownListSelectAccount
ORDER BY Date DESC";
cmd.Parameters.Add("#DropDownListSelectAccount", SqlDbType.VarChar, 50). Value) = DropDownListSelectAccount.SelectedValue;
By the way, you don't need to cast Debit_From as a varchar, since it's already like that in your database.

Answer 2

This is your query:
select Date as Date, Credit, Debit_From as Received_From,
Credit_Amount as amount, Reason
from Transaction_Credit
where Credit = " + DropDownListSelectAccount.SelectedValue+ " or
cast(Debit_From as varchar) = " + DropDownListSelectAccount.SelectedValue + "
order by Date DESC;
The code reading this is:
int amount = Convert.ToInt32(rd[2]);
But the 3rd column is Received_From, not amount. That is probably your problem.
Also, cast(Debit_From as varchar) is very dangerous. When you don't include a length for varchar(), SQL Server inserts a length depending on the context. Just don't do a conversion where you don't need one.