/**
* INTERNAL: Returns the first field from each of the owned tables, used for fine-grained
* pessimistic locking.
*/
protected Vector getForUpdateOfFields() {
Vector allFields = getFields();
int expected = getTableAliases().size();
Vector firstFields = new Vector(expected);
DatabaseTable lastTable = null;
DatabaseField field = null;
int i = 0;
// The following loop takes O(n*m) time. n=# of fields. m=#tables.
// However, in the m=1 case this will take one pass only.
// Also assuming that fields are generally sorted by table, this will
// take O(n) time.
// An even faster way may be to go getDescriptor().getAdditionalPrimaryKeyFields.
while ((i < allFields.size()) && (firstFields.size() < expected)) {
field = (DatabaseField) allFields.elementAt(i++);
if ((lastTable == null) || !field.getTable().equals(lastTable)) {
lastTable = field.getTable();
int j = 0;
while (j < firstFields.size()) {
if (lastTable.equals(((DatabaseField) firstFields.elementAt(j)).getTable())) {
break;
}
j++;
}
if (j == firstFields.size()) {
firstFields.addElement(field);
}
}
}
return firstFields;
}
