Why Does My MySQL Parameterized Query in C# Throw an IndexOutOfBoundsException?

Parameterized Queries for MySQL with C#

This question addresses a common issue encountered when using parameterized queries with MySQL in C#. The provided code includes the relevant parts of the code that raise the issue.

Question:

The code snippet includes a parameterized query with two question marks (?) as placeholders for parameter values. However, the user experiences an IndexOutOfBoundsException when adding the first parameter. What's wrong with the code?

Answer:

The provided code initializes the MySqlCommand object with a parameterized query, but the placeholder question marks are not prefixed with the "@" character, which is required for named parameters in MySQL. The corrected code is as follows:

private String readCommand = 
             "SELECT LEVEL FROM USERS WHERE VAL_1 = @param_val_1 AND VAL_2 = @param_val_2;";

public bool read(string id)
{
    level = -1;
    MySqlCommand m = new MySqlCommand(readCommand);
    m.Parameters.AddWithValue("@param_val_1", val1);
    m.Parameters.AddWithValue("@param_val_2", val2);
    level = Convert.ToInt32(m.ExecuteScalar());
    return true;
}

In this corrected code:

• The readCommand string is modified to use named parameters with "@param_name" syntax.
• The AddWithValue method is used to add the parameters to the command, ensuring the parameter names match those specified in the query.
• The ExecuteScalar method is used to execute the query and retrieve a single scalar value (the level in this case).

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