# Extra Models

Continuing with the previous example, it will be common to have more than one related model.

This is especially the case for user models, because:

* The **input model** needs to be able to have a password.
* The **output model** should not have a password.
* The **database model** would probably need to have a hashed password.

!!! danger
    Never store user's plaintext passwords. Always store a "secure hash" that you can then verify.

    }

    override fun clearCaches() {
        cache.clear()
    }

    /**
     * Note: Races cannot happen because the listener is guaranteed to be invoked in a write action.
     */
    internal class SessionInvalidationListener(val project: Project) : LLFirSessionInvalidationListener {

    } else if (bufferSize < k) {
      buffer[bufferSize++] = elem;
      // uncheckedCastNullableTToT is safe because bufferSize > 0.
      if (comparator.compare(elem, uncheckedCastNullableTToT(threshold)) > 0) {
        threshold = elem;
      }
      // uncheckedCastNullableTToT is safe because bufferSize > 0.
    } else if (comparator.compare(elem, uncheckedCastNullableTToT(threshold)) < 0) {

    C columnKey = columnKeySet().asList().get(columnIndex);
    // requireNonNull is safe because we use indexes that were populated by the constructor.
    V value = requireNonNull(values[rowIndex][columnIndex]);
    return cellOf(rowKey, columnKey, value);
  }

  @Override
  V getValue(int index) {
    // requireNonNull is safe because we use indexes that were populated by the constructor.

    }
  }

  /**
   * This is like [toLowerCase] except that it does nothing if this contains any non-ASCII
   * characters. We want to avoid lower casing special chars like U+212A (Kelvin symbol) because
   * they can return ASCII characters that match real hostnames.
   */
  private fun String.asciiToLowercase(): String {
    return when {
      isAscii() -> lowercase(Locale.US) // This is an ASCII string.

    return CollectCollectors.toImmutableSet();
  }

  /**
   * Returns the empty immutable set. Preferred over {@link Collections#emptySet} for code
   * consistency, and because the return type conveys the immutability guarantee.
   *
   * <p><b>Performance note:</b> the instance returned is a singleton.
   */

      // permitted not to throw because it would be a no-op
    }
    expectUnchanged();
  }

  @MapFeature.Require(value = SUPPORTS_PUT, absent = ALLOWS_NULL_KEY_QUERIES)
  public void testReplace_absentNullKeyUnsupported() {
    try {
      getMap().replace(null, v3());
    } catch (NullPointerException tolerated) {
      // permitted not to throw because it would be a no-op
    }
    expectUnchanged();
  }

    } catch (ExecutionException e) {
      builder.append("FAILURE, cause=[").append(e.getCause()).append("]");
    } catch (CancellationException e) {
      builder.append("CANCELLED");
    } catch (RuntimeException e) {
      builder.append("UNKNOWN, cause=[").append(e.getClass()).append(" thrown from get()]");
    }
  }

  private enum State {
    PENDING {

        case -2:
          // requireNonNull is safe because right must exist in order to get a negative factor.
          requireNonNull(right);
          if (right.balanceFactor() > 0) {
            right = right.rotateRight();
          }
          return rotateLeft();
        case 2:
          // requireNonNull is safe because left must exist in order to get a positive factor.
          requireNonNull(left);

          return of();
        case 1:
          /*
           * requireNonNull is safe because we ensure that the first `distinct` elements have been
           * populated.
           */
          return of(requireNonNull(dedupedElements[0]));
        default:
          /*
           * The suppression is safe because we ensure that the first `distinct` elements have been
           * populated.
           */