I m trying to use the JPA2 metadata to figure out the order to insert/delete rows from a database so constraints are not an issue (to be used later in Java code). This is part of a backup/restore approach using JPA.

Here s my approach:

1. Group tables by amount of relationships/constraints (Only one-to-many and one-to-one are considered)
2. Tables with zero instances (as per #1) can have records added/deleted without issue
3. Tables with one instance can have records added/deleted without issue as long as the related table is already "ready"

Ready by ready I mean that all its related tables records are populated so foreign keys are valid for insert or that there are no other tables referencing to records in this table.

I m sure it ll be some kind of recursive approach but I got stuck. Any help is more than welcomed.

Here s the code so far:

/**
 * Get the execution order from the EntityManager meta data model.
 *
 * This will fail if the EntityManager is not JP2 compliant
 * @param em EntityManager to get the metadata from
 * @return ArrayList containing the order to process tables
 */
protected static ArrayList<String> getProcessingOrder(EntityManager em) {
    ArrayList<String> tables = new ArrayList<String>();
    //This holds the amount of relationships and the tables with that same amount
    HashMap<Integer, ArrayList<String>> tableStats = new HashMap<Integer, ArrayList<String>>();
    //This holds the table and the tables referenced by it
    HashMap<String, ArrayList<String>> references = new HashMap<String, ArrayList<String>>();
    for (EntityType et : em.getMetamodel().getEntities()) {
        Logger.getLogger(XincoBackupManager.class.getSimpleName()).log(Level.FINER, et.getName());
        int amount = 0;
        Iterator<SingularAttribute> sIterator = et.getSingularAttributes().iterator();
        while (sIterator.hasNext()) {
            SingularAttribute next = sIterator.next();
            switch (next.getPersistentAttributeType()) {
                case BASIC:
                case ELEMENT_COLLECTION:
                case EMBEDDED:
                case ONE_TO_MANY:
                case ONE_TO_ONE:
                    Logger.getLogger(XincoBackupManager.class.getSimpleName()).log(Level.FINER,
                            "Ignoring: {0}", next.getName());
                    break;
                case MANY_TO_MANY:
                case MANY_TO_ONE:
                    Logger.getLogger(XincoBackupManager.class.getSimpleName()).log(Level.INFO,
                            "{3} has a {2} relationship: {0} with: {1}",
                            new Object[]{next.getName(), next.getBindableJavaType(),
                                next.getPersistentAttributeType().name(), et.getName()});
                    if (!references.containsKey(et.getName())) {
                        references.put(et.getName(), new ArrayList<String>());
                    }
                    references.get(et.getName()).add(next.getBindableJavaType().getSimpleName());
                    amount++;
                    break;
                default:
                    Logger.getLogger(XincoBackupManager.class.getSimpleName()).log(Level.SEVERE,
                            "Unexpected value: {0}", next.getName());
                    break;
            }
        }
        Iterator<PluralAttribute> pIterator = et.getPluralAttributes().iterator();
        while (pIterator.hasNext()) {
            PluralAttribute next = pIterator.next();
            switch (next.getPersistentAttributeType()) {
                case BASIC:
                case ELEMENT_COLLECTION:
                case EMBEDDED:
                case ONE_TO_MANY:
                case MANY_TO_MANY:
                    Logger.getLogger(XincoBackupManager.class.getSimpleName()).log(Level.FINER,
                            "Ignoring: {0}", next.getName());
                    break;
                case MANY_TO_ONE:
                case ONE_TO_ONE:
                    Logger.getLogger(XincoBackupManager.class.getSimpleName()).log(Level.INFO,
                            "{3} has a {2} relationship: {0} with: {1}",
                            new Object[]{next.getName(), next.getBindableJavaType(),
                                next.getPersistentAttributeType().name(), et.getName()});
                    if (!references.containsKey(et.getName())) {
                        references.put(et.getName(), new ArrayList<String>());
                    }
                    references.get(et.getName()).add(next.getBindableJavaType().getSimpleName());
                    amount++;
                    break;
                default:
                    Logger.getLogger(XincoBackupManager.class.getSimpleName()).log(Level.SEVERE,
                            "Unexpected value: {0}", next.getName());
                    break;
            }
        }
        if (!tableStats.containsKey(amount)) {
            tableStats.put(amount, new ArrayList<String>());
        }
        tableStats.get(amount).add(et.getName());
    }
    Iterator<String> iterator = references.keySet().iterator();
    while (iterator.hasNext()) {
        String next = iterator.next();
        Iterator<String> iterator1 = references.get(next).iterator();
        StringBuilder refs = new StringBuilder();
        while (iterator1.hasNext()) {
            refs.append(iterator1.next()).append("
");
        }
        Logger.getLogger(XincoBackupManager.class.getSimpleName()).log(Level.FINER, "References for {0}:
{1}", new Object[]{next, refs.toString()});
    }
    //Need to sort entities with relationships even further
    ArrayList<String> temp = new ArrayList<String>();
    for (Entry<Integer, ArrayList<String>> e : tableStats.entrySet()) {
        if (e.getKey() > 0) {
            Logger.getLogger(XincoBackupManager.class.getSimpleName()).log(Level.INFO, "Tables with {0} references", e.getKey());
            for (String t : e.getValue()) {
                //Check the relationships of the tables
                //Here s where I need help
                boolean ready = true;
                for (String ref : references.get(t)) {
                    if (!temp.contains(ref)) {
                        Logger.getLogger(XincoBackupManager.class.getSimpleName()).log(Level.INFO,
                                "{0} is not ready. Referenced table {1} is not ready yet", new Object[]{t, ref});
                        ready = false;
                    }
                }
                if (ready) {
                    Logger.getLogger(XincoBackupManager.class.getSimpleName()).log(Level.INFO, "{0} is ready.", t);
                    temp.add(t);
                }
            }
            //-------------------------------------------------------
        } else {
            temp.addAll(e.getValue());
        }
    }
    for (Entry<Integer, ArrayList<String>> e : tableStats.entrySet()) {
        Logger.getLogger(XincoBackupManager.class.getSimpleName()).log(Level.FINER,
                "Amount of relationships: {0}", e.getKey());
        StringBuilder list = new StringBuilder();
        for (String t : e.getValue()) {
            list.append(t).append("
");
        }
        Logger.getLogger(XincoBackupManager.class.getSimpleName()).log(Level.FINER, list.toString());
    }
    tables.addAll(temp);
    return tables;
}