Having a problem inserting a foreign key data into a table using a PHP form

I am newbee with PHP and MySQL and need help...

I have two tables (Staff and Position) in the database. The Staff table (StaffId, Name, PositionID (fk)). The Position table is populated with different positions (Manager, Supervisor, and so on). The two tables are linked with a PositionID foreign key in the Staff table. I have a staff registration form with textfields asking for the relevant attributes and a dynamically populated drop down list to choose the position. I need to insert the user's entry into the staff table along with the selected position. However, when inserting the data, I get the following error (Cannot add or update a child row: a foreign key constraint fails). How do I insert the position selected by the user into the staff table?

Here is some of my code...

...
echo "<tr>";
echo "<td>";
echo "*Position:"; 
echo "</td>";
echo "<td>";

//dynamically populate the staff position drop down list from the position table
$position="SELECT PositionId, PositionName
            FROM Position
            ORDER BY PositionId";
$exeposition = mysql_query ($position) or die (mysql_error());
echo "<select name=position value=''>Select Position</option>";
while($positionarray=mysql_fetch_array($exeposition))
{
echo "<option value=$positionarray[PositionId]>$positionarray[PositionName]</option>";
}
echo "</select>";   
echo "</td>";
echo "</tr>"

//the form is processed with the code below

$FirstName = $_POST['firstname'];
$LastName = $_POST['lastname'];
$Address = $_POST['address'];
$City = $_POST['city'];
$PostCode = $_POST['postcode'];
$Country = $_POST['country'];
$Email = $_POST['email'];
$Password = $_POST['password'];
$ConfirmPass = $_POST['confirmpass'];
$Mobile = $_POST['mobile'];
$NI = $_POST['nationalinsurance'];
$PositionId = $_POST[$positionarray['PositionId']];

//format the dob for the database
$dobpart = explode("/", $_POST['dob']);
$formatdob = $dobpart[2]."-".$dobpart[1]."-".$dobpart[0];
$DOB = date("Y-m-d", strtotime($formatdob));

$newReg = "INSERT INTO Staff (FirstName, LastName, Address, City, PostCode,     
Country, Email, Password, Mobile, DOB, NI, PositionId) VALUES ('".$Fi开发者_JAVA技巧rstName."', 
'".$LastName."', '".$Address."', '".$City."', '".$PostCode."', '".$Country."',  
'".$Email."', '".$Password."', ".$Mobile.", '".$DOB."', '".$NI."', '".$PostionId."')";

Your time and help is surely appreciated.

You seem to have a typo in the INSERT. The variable $PostionId should be $PositionId.

In addition, make sure you understand that you code is vulnerable to SQL Injection.

In your insert SQL query, you are using this :

, '".$PostionId."')"

While, a few lines before, you are declaring :

$PositionId = $_POST[$positionarray['PositionId']];

The variable used in the insert query is not the same as the one containing the data : it lacks a i -- which, I suppose, is bad.

If this not enough to solve your problem, echoing your SQL query before executing it might help you figure out what is wrong in it.

This kind of error, about foreign keys, is generally caused by inserting a wrong id -- that doesn't have a corresponding row in the referenced table.

Aside from that, your code is vulnerable to SQL injections : you should escape and filter your data.

For string values, you can use mysql_real_escape_string :

$FirstName = mysql_real_escape_string($_POST['firstname']);

For integer values, you can make sure you are injecting integers in the SQL query, using, for instance, intval :

$data = intval($_POST['data']);

(Not sure you have an integer value here, so I just took 'data' as an example)