Nested dropdown - php

Question

I'm building a form with php/mysql. I've got a table with a list of locations and sublocations. Each sublocation has a parent location. A column "parentid" references another locationid in the same table. I now want to load these values into a dropdown in the following manner:
--Location 1
----Sublocation 1
----Sublocation 2
----Sublocation 3
--Location 2
----Sublocation 4
----Sublocation 5
etc. etc.
Did anyone get an elegant solution for doing this?

Answer 1

NOTE: This is only psuedo-code.. I didn't try running it, though you should be able to adjust the concepts to what you need.
$parentsql = "SELECT parentid, parentname FROM table";
$result = mysql_query($parentsql);
print "<select>";
while($row = mysql_fetch_assoc($result)){
$childsql = "SELECT childID, childName from table where parentid=".$row["parentID"];
$result2 = mysql_query($childsql);
print "<optgroup label=\".$row["parentname"]."\">";
while($row2 = mysql_fetch_assoc($result)){
print "<option value=\"".$row["childID"]."\">".$row["childName"]."</option>\n";
}
print "</optgroup>";
}
print "</select>";
With BaileyP's valid criticism in mind, here's how to do it WITHOUT the overhead of calling multiple queries in every loop:
$sql = "SELECT childId, childName, parentId, parentName FROM child LEFT JOIN parent ON child.parentId = parent.parentId ORDER BY parentID, childName";
$result = mysql_query($sql);
$currentParent = "";
print "<select>";
while($row = mysql_fetch_assoc($result)){
if($currentParent != $row["parentID"]){
if($currentParent != ""){
print "</optgroup>";
}
print "<optgroup label=\".$row["parentName"]."\">";
$currentParent = $row["parentName"];
}
print "<option value=\"".$row["childID"]."\">".$row["childName"]."</option>\n";
}
print "</optgroup>"
print "</select>";

Answer 2

Are you looking for something like the OPTGROUP tag?

Answer 3

optgroup is definitely the way to go. It's actually what it's for,
For example usage, view source of http://www.grandhall.eu/tips/submit/ - the selector under "Grandhall Grill Used".

Answer 4

You can use and space/dash indentation in the actual HTML. You'll need a recusrive loop to build it though. Something like:
<?php
$data = array(
'Location 1' => array(
'Sublocation1',
'Sublocation2',
'Sublocation3' => array(
'SubSublocation1',
),
'Location2'
);
$output = '<select name="location">' . PHP_EOL;
function build_items($input, $output)
{
if(is_array($input))
{
$output .= '<optgroup>' . $key . '</optgroup>' . PHP_EOL;
foreach($input as $key => $value)
{
$output = build_items($value, $output);
}
}
else
{
$output .= '<option>' . $value . '</option>' . PHP_EOL;
}
return $output;
}
$output = build_items($data, $output);
$output .= '</select>' . PHP_EOL;
?>
Or something similar ;)

Answer 5

Ideally, you'd select all this data in the proper order right out of the database, then just loop over that for output. Here's my take on what you're asking for
<?php
/*
Assuming data that looks like this
locations
+----+-----------+-------+
| id | parent_id | descr |
+----+-----------+-------+
| 1 | null | Foo |
| 2 | null | Bar |
| 3 | 1 | Doe |
| 4 | 2 | Rae |
| 5 | 1 | Mi |
| 6 | 2 | Fa |
+----+-----------+-------+
*/
$result = mysql_query( "SELECT id, parent_id, descr FROM locations order by coalesce(id, parent_id), descr" );
echo "<select>";
while ( $row = mysql_fetch_object( $result ) )
{
$optionName = htmlspecialchars( ( is_null( $row->parent_id ) ) ? "--{$row->descr}" : "----{$row->desc}r", ENT_COMPAT, 'UTF-8' );
echo "<option value=\"{$row->id}\">$optionName</option>";
}
echo "</select>";
If you don't like the use of the coalesce() function, you can add a "display_order" column to this table that you can manually set, and then use for the ORDER BY.