sclass HCRUD_Concepts<A extends Concept> extends HCRUD_Data {
  Concepts cc = db_mainConcepts();
  Class<A> cClass;
  new L<IVF1<A>> onCreateOrUpdate;
  IVF2<A, MapSO> afterUpdate; // parameter 2: old values
  MapSO filters; // fields to filter by/add to new objects
  ValueConverterForField valueConverter;
  bool referencesBlockDeletion;
  bool trimAllSingleLineValues;
  Set<S> fieldsToHideInCreationForm;
  bool lockDB; // lock DB while updating object
  bool verbose;
  bool dropEmptyListValues = true;
  bool lsMagic;
  
  bool useDynamicComboBoxes; // dynamically load concepts combo box entries for all fields
  IPred<S> useDynamicComboBoxesForField; // activate dynamic combo boxes for selected fields
  int dynamicComboBoxesThreshold = 1000; // if there are this many entries or more, use a dynamic combo box
  
  *(Class<A> *cClass) {}
  
  // XXX - breaking change from just shortName()
  swappable S itemName() { ret humanizeShortName(cClass); }
  swappable S itemNamePlural() { ret super.itemNamePlural(); }
  
  //LS fields() { ret conceptFields(cClass); }
  
  L<A> itemsForListing() {
    ret defaultSort(asList(listConcepts()));
  }
  
  @Override
  L<MapSO> list() {
    ret lambdaMap itemToMapForList(itemsForListing());
  }
  
  // more efficient version - convert items only after taking subList
  // TODO: this is never called by HCRUD; make lazy list instead?
  @Override
  L<MapSO> list(IntRange range) {
    ret lambdaMap itemToMapForList(subListOrFull(itemsForListing(), range));
  }
  
  Cl<A> listConcepts() {
    ret conceptsWhere(cc, cClass, mapToParams(filters));
  }
  
  L<A> defaultSort(L<A> l) { ret l; }
  
  swappable MapSO emptyObject() {
    A c = unlisted(cClass);
    ret mapMinusKeys(fieldsToHideInCreationForm, itemToMap(c));
  }
  
  MapSO itemToMap(A c) {
    if (c == null) null;
    ret putKeysFirst(getFieldOrder(c), conceptToMap_gen_withNullValues(c));
  }
  
  MapSO itemToMapForList(A c) {
    if (c == null) null;
    MapSO map = itemToMap(c);
    massageItemMapForList(c, map);
    ret map;
  }
  
  swappable void massageItemMapForList(A c, MapSO map) {
  }
  
  swappable void massageItemMapForUpdate(A c, MapSO map) {
    // Concepts.RefL magic
    
    for (Field f : nonStaticNonTransientFieldObjectsOfType(Concept.RefL.class, cClass)) {
      new TreeMap<Int, O> values;
      new Matches m;
      for (S key, O value : cloneMap(map))
        if (startsWith(key, f.getName() + "_", m) && isInteger(m.rest())) {
          long conceptID = parseFirstLong((S) value);
          Concept concept = getConcept(cc, conceptID);
          printVars_str("RefL magic", +key, +conceptID, +concept);
          if (concept != null || !dropEmptyListValues)
            values.put(parseInt(m.rest()), concept);
          map.remove(key);
        }
        
      if (!dropEmptyListValues)
        while (nempty(values) && lastValue(values) == null) {
          if (verbose) print("Dropping value " + lastEntry(values));
          removeLastKey(values);
        }
        
      map.put(f.getName(), valuesAsList(values));
    }
    
    // Concepts.Ref magic (look up concept)
    
    for (Field f : nonStaticNonTransientFieldObjectsOfType(Concept.Ref.class, cClass)) {
      O value = map.get(f.getName());
      if (value cast S) {
        long conceptID = parseFirstLong(value);
        Concept concept = getConcept(cc, conceptID);
        map.put(f.getName(), concept);
      }
    }
    
    // trim values
    
    if (trimAllSingleLineValues)
      for (Map.Entry<S, O> e : map.entrySet()) {
        S val = optCastString(e.getValue());
        if (val != null && isSingleLine(val) && isUntrimmed(val))
          e.setValue(trim(val));
      }

    // LS magic
    
    if (lsMagic)
     for (Field f : nonStaticNonTransientFieldObjectsOfType(L.class, cClass)) {
      if (eqOneOf(f.getName(), "refs", "backRefs")) continue;
      new TreeMap<Int, S> values;
      new Matches m;
      
      for (S key, O value : cloneMap(map)) {
        if (startsWith(key, f.getName() + "_", m) && isInteger(m.rest())) {
          if (!dropEmptyListValues || nempty((S) value)) {
            if (verbose) print("Adding value " + m.rest() + " / " + value);
            mapPut(values, parseInt(m.rest()), (S) value);
          }
          map.remove(key);
        }
      }
      
      if (!dropEmptyListValues)
        while (nempty(values) && empty(lastValue(values))) {
          if (verbose) print("Dropping value " + lastEntry(values));
          removeLastKey(values);
        }
        
      map.put(f.getName(), valuesAsList(values));
    }
    
    // don't set SecretValue fields
    
    for (Field f : nonStaticNonTransientFieldObjectsOfType(SecretValue, cClass))
      map.remove(f.getName());
  }
  
  swappable MapSO getObject(O id) {
    ret itemToMap(conceptForID(id));
  }
  
  O createObject(SS fullMap, S fieldPrefix) {
    SS map = extractFieldValues(fullMap, fieldPrefix);
    A c = cnew(cc, cClass);
    // make sure filters override
    setValues(c, mapMinusKeys(map, filteredFields()), true);
    cset(c, mapToParams(filters));
    pcallFAll(onCreateOrUpdate, c);
    ret c.id;
  }
  
  void setValues(A c, SS map, bool creating) {
    lock lockDB && !creating ? dbLock(cc) : null;
    MapSO map2 = (Map) cloneMap(map);
    massageItemMapForUpdate(c, map2);
    if (verbose) {
      print("setValues " + map);
      print("backRefs: " + c.backRefs);
    }
    MapSO oldValues = !creating && afterUpdate != null
      ? cgetAll_cloneLists(c, keys(map2)) : null;
    if (valueConverter == null)
      cSmartSet(c, mapToParams(map2));
    else
      cSmartSet_withConverter(verbose, valueConverter, c, mapToParams(map2));
    if (oldValues != null)
      callF(afterUpdate, c, oldValues);
    if (verbose)
      print("backRefs: " + c.backRefs);
  }
  
  A conceptForID(O id) {
    ret getConcept(cc, cClass, toLong(id));
  }
  
  S updateObject(O id, SS fullMap, S fieldPrefix) {
    SS map = extractFieldValues(fullMap, fieldPrefix);
    A c = conceptForID(id);
    if (c == null) ret "Object " + id + " not found";
    try answer checkFilters(c);
    setValues(c, map, false);
    pcallFAll(onCreateOrUpdate, c);
    ret "Object " + id + " updated";
  }
  
  S deleteObject(O id) {
    A c = conceptForID(id);
    if (c == null) ret "Object " + id + " not found";
    try answer checkFilters(c);
    actuallyDeleteConcept(c);
    ret "Object " + id + " deleted";
  }
  
  swappable void actuallyDeleteConcept(A c) {
    deleteConcept(c);
  }
  
  S checkFilters(A c) {
    ret checkConceptFields(c, mapToParams(filters)) ? "" : "Object " + c.id + " not in view";
  }
  
  HCRUD_Concepts<A> addFilters(MapSO map) {
    fOr (S field, O value : map)
      addFilter(field, value);
    this;
  }
  
  HCRUD_Concepts<A> addFilter(S field, O value) {
    filters = orderedMapPutOrCreate(filters, field, value);
    this;
  }
  
  Renderer getRenderer(S field) {
    Class type = fieldType(cClass, field);
    
    if (eq(type, bool.class))
      ret new CheckBox;
      
    if (eq(type, Bool.class))
      ret new ComboBox(ll("", "yes", "no"),
        b -> trueFalseNull((Bool) b, "yes", "no", ""));
    
    // show a Ref<> field as a combo box
    
    if (eq(type, Concept.Ref.class)) {
      Class<? extends Concept> c = getTypeArgumentAsClass(genericFieldType(cClass, field));
      ret makeConceptsComboBox(field, c);
    }
    
    // show dynamic field with concept value as combo box
    
    O val = mapGet(item, field);
    if (val cast Concept) {
      Class<? extends Concept> c = val.getClass();
      ret makeConceptsComboBox(field, c);
    }
    
    // show a RefL<> field as a list of combo boxes
    
    if (eq(type, Concept.RefL.class)) {
      Class<? extends Concept> c = getTypeArgumentAsClass(genericFieldType(cClass, field));
      ret new FlexibleLengthList(makeConceptsComboBox(field, c));
    }
    
    ret super.getRenderer(field);
  }
  
  DynamicComboBox makeDynamicComboBox(S field, Class<? extends Concept> c) {
    DynamicComboBox cb = new(field);
    cb.valueToEntry = value -> {
      value = deref(value);
      //print("ComboBox: value type=" + _getClass(value);
      long id = 0;
      if (value cast Concept) id = conceptID(value);
      else if (value instanceof S && isInteger((S) value)) id = parseLong(value);
      if (id != 0)
        ret comboBoxItem(getConcept(cc, id));
      null;
    };
    ret cb;
  }

  AbstractComboBox makeConceptsComboBox(S field, Class<? extends Concept> c) {
    if (useDynamicComboBoxes || useDynamicComboBoxesForField != null && useDynamicComboBoxesForField.get(field))
      ret makeDynamicComboBox(field, c);
    
    LS entries = comboBoxItemsForConceptClass(c);
    if (l(entries) >= dynamicComboBoxesThreshold)
      ret makeDynamicComboBox(field, c);

    ComboBox cb = new(entries);
    cb.valueToEntry = value -> {
      value = deref(value);
      //print("ComboBox: value type=" + _getClass(value);
      long id = 0;
      if (value cast Concept) id = conceptID(value);
      else if (value instanceof S && isInteger((S) value)) id = parseLong(value);
      if (id != 0) {
        S entry = firstWhereFirstLongIs(entries, id);
        //print("combobox selected: " + id + " / " + entry);
        ret entry;
      }
      null;
    };
    ret cb;
  }
  
  // TODO: filters!
  LS comboBoxItemsForConceptClass(Class<? extends Concept> c) {
    ret comboBoxItems(cc.list(c));
  }
  
  LS comboBoxItems(Cl<? extends Concept> l) {
    ret itemPlus("", lmap comboBoxItem(l));
  }
  
  S comboBoxItem(Concept val) {
    ret val == null ? null : shorten(val.id + ": " + val);
  }
  
  bool objectCanBeDeleted(O id) {
    ret !referencesBlockDeletion || !hasBackRefs(conceptForID(id));
  }
  
  Set<S> filteredFields() { ret keys(filters); }
  
  LS comboBoxSearch(S info, S query) {
    // info is the field name (Ref or RefL). get concept class
    S field = info;
    Class<? extends Concept> c = getTypeArgumentAsClass(genericFieldType(cClass, field));
    if (c == null) null;
    LS items = comboBoxItemsForConceptClass(c);
    ret takeFirst(10, scoredSearch(query, items));
  }
  
  // to find the concept e.g. within massageFormMatrix
  A conceptForMap(MapSO map) {
    if (map == null) null;
    Long id = cast map.get(idField());
    ret id == null ?: (A) getConcept(cc, id);
  }
  
  SS extractFieldValues(SS fullMap, S fieldPrefix) {
    ret subMapStartingWith_dropPrefix(fullMap, fieldPrefix);
  }
}