Why Am I Getting a 'Person Column Cannot Be Null' Error When Inserting Data into MySQL with C#?

C# with MySQL INSERT Parameters

Utilizing parameters in MySQL INSERT statements is a crucial practice for maintaining data integrity and preventing SQL injection attacks. However, you've encountered issues with your code, and we're here to assist you in resolving them.

Original Issue:

In your initial code, you attempted to execute an INSERT statement with parameters using:

comm.Parameters.Add("@person", "Myname");
comm.Parameters.Add("@address", "Myaddress");

However, the error message "Person column cannot be null" indicates that you have missed setting a value for the person parameter.

Solution:

To address this issue, you need to assign values to the parameters:

comm.Parameters.Add("@person", MySqlDbType.VarChar).Value = "Myname";
comm.Parameters.Add("@address", MySqlDbType.VarChar).Value = "Myaddress";

SQL Injection Vulnerability:

You've also mentioned that using a literal string in the INSERT statement (e.g., "INSERT INTO room(person,address) VALUES('Myname', 'Myaddress')") does not produce an error. However, this practice is prone to SQL injection attacks, where malicious users can manipulate the input to execute arbitrary SQL commands.

Alternative Solution:

Instead, you can use the AddWithValue method, which automatically handles parameterization and prevents SQL injection:

comm.Parameters.AddWithValue("@person", "Myname");
comm.Parameters.AddWithValue("@address", "Myaddress");

Using Question Marks:

Another option is to use question marks as placeholders for parameters, like:

comm.CommandText = "INSERT INTO room(person,address) VALUES(?person, ?address)";
comm.Parameters.Add("?person", "Myname");
comm.Parameters.Add("?address", "Myaddress");

Ensure that you specify the MySQL data type for each parameter using the MySqlDbType enum.

Index-Based Parameters:

Your attempt to use index-based parameters (e.g., cmd.Parameters.Add("person", MySqlDbType.VarChar).Value = a;) is not valid. The index-based approach is for stored procedures, not parameterized queries.

Solved Code:

Ultimately, your code was resolved by using the following approach:

cmd.CommandText = "INSERT INTO room(person,address) VALUES(?person,?address)";
cmd.Parameters.Add("?person", MySqlDbType.VarChar).Value = "myname";
cmd.Parameters.Add("?address", MySqlDbType.VarChar).Value = "myaddress";
cmd.ExecuteNonQuery();

This code successfully executes the INSERT statement while protecting against SQL injection.

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