Auto increment number

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i want to know that how to make auto-increment id in asp.net/C# i need display in textbox here my code is

con.Open();
int a=0;
SqlCommand com = new SqlCommand("select max(makeid) from make",con);
SqlDataReader dr = com.ExecuteReader();
if(dr.Read())
{
   a = Convert .ToInt32 (dr[0].ToString ())+1;(here show the error)
}
txtmakeid.Text = Convert.ToString(a);
con.Close();

But i got error is "Input string was not in a correct format." how to solve this one

Posted 15-Feb-12 23:30pm

Member 8614787

Updated 15-Feb-12 23:36pm

Varun Sareen

v3

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Herman<T>.Instance · Answer 1 · 2012-02-15T23:38:00

Solution 1

C#

a = dr[0] == DBNull.Value ? 0 : Convert.ToInt32(dr[0]) +1;

Posted 15-Feb-12 23:38pm

Herman<T>.Instance

Comments

Member 8614787 16-Feb-12 5:47am

Thanks for reply but i got only for o values not 1

OriginalGriff · Answer 2 · 2012-02-15T23:41:00

Solution 2

Even if you do solve it, that is a dangerous way to do it.
What happens if a different user calls that same code at the same time? Or even after you do this, but before you add your record to the database? Answer: you both end up with the same number.
First off: ditch the conversions, and return it via a scalar:

C#

con.Open();
int a=0;
SqlCommand com = new SqlCommand("select max(makeid) from make",con);
int a = com.ExecuteScalar();
txtmakeid.Text = Convert.ToString(a);
con.Close();

Which would cure your immediate problem.

But it won't solve the duplicate values!

Posted 15-Feb-12 23:41pm

OriginalGriff

Comments

Member 8614787 16-Feb-12 5:46am

Thanks for your reply, but i need incerament the values in my table is makeid field here automatically increse the values in one by one (ex:1,2,3..)

OriginalGriff 16-Feb-12 6:05am

You can't do that until you write your row into the DB - and then if it is an autoincrement field the value will be assigned by the DB, not you anyway - so the value you are displaying in your text box may have no bearing on the value the row gets when it is written.

Varun Sareen · Answer 3 · 2012-02-15T23:43:00

Solution 3

Dear Friend,

Try this :-

a = dr[0] == DBNUll.Value ? 0 : dr.GetInt32(0) +1;

I hope this will work.

Posted 15-Feb-12 23:43pm

Varun Sareen

Comments

Member 8614787 16-Feb-12 6:09am

hi i got the answer in this code i replace 0 is 1[ a = dr[0] == DBNUll.Value ? 1 : dr.GetInt32(0) +1;] after it's increament from 1,2.. work fine thanks for reply thank you

Varun Sareen 16-Feb-12 11:40am

Dear Friend,

Then Please accept this as your answer or rate it :)

Thanks