/**
* This method can update the values in mulitple database rows for a colum with
* a unique index, without violating that constraint.
*
* Suppose we have a table with a unique index on (otherid, sortorder), and
* for a particular value of otherid, we want to change all the sort orders.
* You have to do this carefully or you will violate the unique index at some time.
* This method takes care of the details for you.
*
* Note that, it is the responsibility of the caller to make sure that the
* requested rename is legal. For example, if you ask for [1 => 2, 2 => 2]
* then you will get a unique key violation error from the database.
*
* @param string $table The database table to modify.
* @param string $field the field that contains the values we are going to change.
* @param array $newvalues oldvalue => newvalue how to change the values.
* E.g. [1 => 4, 2 => 1, 3 => 3, 4 => 2].
* @param array $otherconditions array fieldname => requestedvalue extra WHERE clause
* conditions to restrict which rows are affected. E.g. array('otherid' => 123).
* @param int $unusedvalue (defaults to -1) a value that is never used in $ordercol.
*/
function update_field_with_unique_index($table, $field, array $newvalues, array $otherconditions, $unusedvalue = -1)
{
global $DB;
$safechanges = decompose_update_into_safe_changes($newvalues, $unusedvalue);
$transaction = $DB->start_delegated_transaction();
foreach ($safechanges as $change) {
list($from, $to) = $change;
$otherconditions[$field] = $from;
$DB->set_field($table, $field, $to, $otherconditions);
}
$transaction->allow_commit();
}
public function test_decompose_update_into_safe_changes_string_values()
{
// Sometimes this happens when data has been loaded from the database.
$this->assertEquals(array(array(1, -1), array(2, 1), array(3, 2), array(4, 3), array(-1, 4)), decompose_update_into_safe_changes(array(1 => '4', 2 => '1', 3 => '2', 4 => '3'), -1));
}
