# MgGrid — Layout Persistence

> Part of the MgGrid system. See `README.md` for overview and component hierarchy.

## Storage Keys

Grid layouts are stored in **localStorage** with structured keys:

```
AutoSave: {AutoSaveLayoutName}_{MasterOrParentTypeName}_AutoSave_{UserId}
UserSave: {AutoSaveLayoutName}_{MasterOrParentTypeName}_UserSave_{UserId}
Splitter: Splitter_{grid.AutomaticLayoutStorageKey}
```

**Examples:**
```
GridOrder_Master_AutoSave_42          ← master grid, user #42
GridOrder_Order_AutoSave_42           ← detail grid under Order parent
GridOrder_Master_UserSave_42          ← manually saved layout
Splitter_GridOrder_Master_AutoSave_42 ← splitter pane size
```

## Three Layout Tiers

| Tier | Key Contains | When Saved | When Loaded |
|---|---|---|---|
| **Default** | (in-memory `_defaultLayoutJson`) | First `LayoutAutoLoading` — captures layout before any load | `ResetLayoutAsync()` — restores original |
| **AutoSave** | `_AutoSave_` | Every `LayoutAutoSaving` event (on any layout change) | Every `LayoutAutoLoading` event (on grid init, wrapped in `BeginUpdate`/`EndUpdate`) |
| **UserSave** | `_UserSave_` | `SaveUserLayoutAsync()` — explicit user action | `LoadUserLayoutAsync()` — explicit user action |

## Layout Operations

| Method | Behavior |
|---|---|
| `SaveUserLayoutAsync()` | Saves current layout to both UserSave AND AutoSave keys |
| `LoadUserLayoutAsync()` | Loads from UserSave key (if exists) |
| `ResetLayoutAsync()` | Removes AutoSave key, restores in-memory `_defaultLayoutJson` |
| `HasUserLayoutAsync()` | Checks if UserSave key exists in localStorage |

## Persisted State

The layout (`GridPersistentLayout`) includes: column order, column widths, sort descriptors, group descriptors, filter row values, page size — serialized as JSON via `System.Text.Json`.

## User Identification

`GetLayoutUserId()` is virtual — defaults to `0`. Override in project adapter to provide the logged-in user's ID.