Data type mismatch in criteria expression

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I have a table in access db that has 3 cloumns- Guest_id(Number), Guest_name(Text), Rooms(Text). I get an error on the 5th line when i execute the code saying Data type mismatch in criteria expression . I dont know what the problem is. Please help. Thanks in advance.

C#

cn.Open();
cmd.Connection = cn;
query = "Select * from Guest where Guest_id = '"+Convert.ToInt32(guestid_comboBox.Text)+"'";
cmd = new OleDbCommand(query, cn);
dr = cmd.ExecuteReader();
if (dr.Read())
{
   guestname_textBox.Text = dr["Guest_name"].ToString();
}

Posted 14-Aug-11 1:39am

Bennet Ryan

Updated 14-Aug-11 1:40am

Wendelius

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Wendelius · Answer 1 · 2011-08-14T01:43:00

Solution 1

Use the debugger to see what's the value of guestid_comboBox.Text. Most likely you're trying to convert text to a number.

Another thing. Instead of concatenating values directly to an SQL statement, use bind variables instead. See: OleDbParameter[^]

Posted 14-Aug-11 1:43am

Wendelius

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Bennet Ryan 14-Aug-11 7:55am

the value of guestid_comboBox.Text is a number. sorry i didn't understand the material that as there in the link, i'm new to c#.net. If you kindly help me my tell the code to me please. Thank you for your help...

Wendelius 14-Aug-11 8:33am

Ok, the next thing is, is Guest_id numerical or character in the database? If it's numerical, remove the apostrophes:
query = "Select * from Guest where Guest_id = "+Convert.ToInt32(guestid_comboBox.Text);

Bind variables are used instead of literal values in SQL statements, for example typically you don't define a query like
... WHERE SomeField = " + numberVariable;
Instead you should use
... WHERE SomeField = :numberVariable";
and later define the parameter :numberVariable and give it a value. This saves from data type mismatches, sql injections etc.

You can go through the examples in MSDN to get a clear picture. Also here's one good link: http://www.csharp-station.com/Tutorials/AdoDotNet/Lesson06.aspx[^]. That's for different classes (SqlParameter) but the basic idea is the same.