Get the id of inserted row using C#

Question

I have a query to insert a row into a table, which has a field called ID, which is populated using an AUTO_INCREMENT on the column. I need to get this value for the next bit of functionality, but when I run the following, it always returns 0 even though the actual value is not 0:

MySqlCommand comm = connect.CreateCommand();
comm.CommandText = insertInvoice;
comm.CommandText += "\'" + invoiceDate.ToString("yyyy:MM:dd hh:mm:ss") + "\', " + bookFee + ", " + adminFee + ", " + totalFee + ", " + customerID +  ")";
int id = Convert.ToInt32(comm.ExecuteScalar());

According to my understanding, this should return the ID column, but it just returns 0 every time. Any ideas?

EDIT:

When I run:

"INSERT INTO INVOICE (INVOICE_DATE, BOOK_FEE, ADMIN_FEE, TOTAL_FEE, CUSTOMER_ID) VALUES ('2009:01:01 10:21:12', 50, 7, 57, 2134);last_insert_id();"

I get:

{"You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'last_insert_id()' at line 1"}

Answer 1

[Edit: added "select" before references to last_insert_id()]

What about running "select last_insert_id();" after your insert?

MySqlCommand comm = connect.CreateCommand();
comm.CommandText = insertInvoice;
comm.CommandText += "\'" + invoiceDate.ToString("yyyy:MM:dd hh:mm:ss") + "\', "  
    + bookFee + ", " + adminFee + ", " + totalFee + ", " + customerID +  ");";
    + "select last_insert_id();"

int id = Convert.ToInt32(comm.ExecuteScalar());

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Edit: As duffymo mentioned, you really would be well served using parameterized queries like this.

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Edit: Until you switch over to a parameterized version, you might find peace with string.Format:

comm.CommandText = string.Format("{0} '{1}', {2}, {3}, {4}, {5}); select last_insert_id();",
  insertInvoice, invoiceDate.ToString(...), bookFee, adminFee, totalFee, customerID);

Answer 2

It bothers me to see anybody taking a Date and storing it in a database as a String. Why not have the column type reflect reality?

I'm also surprised to see a SQL query being built up using string concatenation. I'm a Java developer, and I don't know C# at all, but I'd wonder if there wasn't a binding mechanism along the lines of java.sql.PreparedStatement somewhere in the library? It's recommended for guarding against SQL injection attacks. Another benefit is possible performance benefits, because the SQL can be parsed, verified, cached once, and reused.

Answer 3

Actually, the ExecuteScalar method returns the first column of the first row of the DataSet being returned. In your case, you're only doing an Insert, you're not actually querying any data. You need to query the scope_identity() after you're insert (that's the syntax for SQL Server) and then you'll have your answer. See here:

Linkage

EDIT: As Michael Haren pointed out, you mentioned in your tag you're using MySql, use last_insert_id(); instead of scope_identity();