> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/Steema/TeeGrid-VCL-FMX-Samples/llms.txt
> Use this file to discover all available pages before exploring further.

# Hierarchical Data (Master-Detail)

> Display nested data with expandable rows

TeeGrid supports hierarchical data through expandable rows, enabling master-detail relationships and multi-level data nesting.

## Overview

Hierarchical data in TeeGrid is implemented using:

* **Expander** - A render that adds expand/collapse icons to rows
* **OnGetData** - Event to provide data for expanded rows
* **OnNewDetail** - Event called when a detail grid is created
* **TRowGroup** - Each expansion level is a separate row group

## Basic Master-Detail Setup

```delphi theme={null}
uses
  Tee.Grid.RowGroup, Tee.Renders;

procedure TForm1.FormCreate(Sender: TObject);
var
  Expander: TExpanderRender;
begin
  // Setup master data
  TeeGrid1.DataSource := CustomersTable;
  
  // Create expander for first column
  Expander := TeeGrid1.Grid.Current.NewExpander;
  Expander.OnGetData := GetOrdersData;
  
  // Set to first column
  if TeeGrid1.Columns.Count > 0 then
    TeeGrid1.Columns[0].Render := Expander;
  
  // Optional: Called when detail grid is created
  TeeGrid1.Grid.Current.OnNewDetail := DetailGridCreated;
end;
```

## OnGetData Event

Provide data for the expanded row:

```delphi theme={null}
procedure TForm1.GetOrdersData(const Sender: TExpanderRender; 
  const ARow: Integer; out AData: TObject);
begin
  // Return data for the detail grid
  AData := TVirtualDBData.From(GetOrdersForCustomer(ARow));
  
  // Grid will destroy the data automatically
  TVirtualDBData(AData).OwnsData := True;
end;
```

## Array Data Master-Detail

```delphi theme={null}
type
  TOrder = record
    OrderID: Integer;
    Date: TDateTime;
    Amount: Double;
  end;
  
  TCustomer = record
    Name: String;
    Orders: TArray<TOrder>;
  end;

var
  Customers: TArray<TCustomer>;

procedure TForm1.GetOrdersData(const Sender: TExpanderRender;
  const ARow: Integer; out AData: TObject);
begin
  // Return orders for this customer
  AData := TVirtualArrayData<TOrder>.Create(Customers[ARow].Orders);
end;
```

## AlwaysExpand Property

Control when expand icons appear:

```delphi theme={null}
// Show expander only when CanExpand returns True
Expander.AlwaysExpand := False;

// Always show expander (determine at expand time if there's data)
Expander.AlwaysExpand := True;
```

## CanExpand Event

Control which rows can be expanded:

```delphi theme={null}
function TForm1.CanExpandRow(const Sender: TRender; 
  const ARow: Integer): Boolean;
begin
  // Only allow expansion if customer has orders
  Result := CustomerHasOrders(ARow);
end;

// Assign to grid
TeeGrid1.Grid.CanExpand := CanExpandRow;
```

## OnNewDetail Event

Customize the detail grid when created:

```delphi theme={null}
procedure TForm1.DetailGridCreated(const Sender, NewGroup: TRowGroup);
begin
  // Customize detail grid appearance
  NewGroup.Rows.Back.Brush.Color := TAlphaColors.Bisque;
  NewGroup.Rows.Back.Brush.Visible := True;
  NewGroup.Cells.Format.Font.Color := TAlphaColors.Darkblue;
  
  // Add totals to detail grid
  AddTotalsToGroup(NewGroup);
  
  // Setup next level of detail (3+ levels)
  SetupNextLevel(NewGroup);
end;
```

## Multi-Level Hierarchies

Create 3+ levels of nesting:

```delphi theme={null}
procedure TForm1.FormCreate(Sender: TObject);
begin
  // Level 1: Customers
  TeeGrid1.DataSource := CustomersTable;
  SetupExpander(TeeGrid1.Grid.Current, GetOrders);
  TeeGrid1.Grid.Current.OnNewDetail := Level2Created;
end;

procedure TForm1.Level2Created(const Sender, NewGroup: TRowGroup);
begin
  // Level 2: Orders
  SetupExpander(NewGroup, GetOrderItems);
  NewGroup.OnNewDetail := Level3Created;
end;

procedure TForm1.Level3Created(const Sender, NewGroup: TRowGroup);
begin
  // Level 3: Order Items (no further expansion)
  NewGroup.Rows.Back.Brush.Color := TAlphaColors.Lavender;
  NewGroup.Rows.Back.Brush.Visible := True;
end;

procedure TForm1.SetupExpander(const AGroup: TRowGroup; 
  const AEvent: TExpanderGetDataEvent);
var
  Expander: TExpanderRender;
begin
  Expander := AGroup.NewExpander;
  Expander.OnGetData := AEvent;
  Expander.AlwaysExpand := True;
  
  if AGroup.Columns.Count > 0 then
    AGroup.Columns[0].Render := Expander;
end;
```

## Database Master-Detail

Using FireDAC with master-detail queries:

```delphi theme={null}
procedure TForm1.GetOrders(const Sender: TExpanderRender;
  const ARow: Integer; out AData: TObject);
var
  CustomerID: Integer;
begin
  // Get CustomerID from master table
  CustomerID := CustomersTable.FieldByName('CustomerID').AsInteger;
  
  // Create detail query
  AData := TVirtualDBData.From(CreateOrdersQuery(CustomerID));
  TVirtualDBData(AData).OwnsData := True;
end;

function TForm1.CreateOrdersQuery(CustomerID: Integer): TDataSet;
var
  Query: TFDQuery;
begin
  Query := TFDQuery.Create(nil);
  Query.Connection := FDConnection1;
  Query.SQL.Text := 'SELECT * FROM Orders WHERE CustomerID = :CustID';
  Query.ParamByName('CustID').AsInteger := CustomerID;
  Query.Open;
  Result := Query;
end;
```

## Programmatic Expansion

Expand/collapse rows programmatically:

```delphi theme={null}
// Expand specific row
TeeGrid1.Grid.Current.ToggleDetail(Expander, RowIndex);

// Expand all rows at level 0
TeeGrid1.Grid.Current.ShowHideAllDetail(0, True);

// Collapse all rows at level 0
TeeGrid1.Grid.Current.ShowHideAllDetail(0, False);
```

## Toggle All Rows Example

```delphi theme={null}
var
  AllExpanded: Boolean;

procedure TForm1.ButtonToggleAllClick(Sender: TObject);
begin
  AllExpanded := not AllExpanded;
  TeeGrid1.Grid.Current.ShowHideAllDetail(0, AllExpanded);
  
  if AllExpanded then
    Button1.Caption := 'Collapse All'
  else
    Button1.Caption := 'Expand All';
end;
```

## Expander Icons

Customize the expand/collapse icons:

```delphi theme={null}
var
  Expander: TExpanderRender;
begin
  Expander := TeeGrid1.Grid.Current.NewExpander;
  
  // Customize icon appearance
  Expander.Format.Stroke.Color := clBlue;
  Expander.Format.Stroke.Width := 2;
  Expander.Format.Brush.Color := clWhite;
  Expander.Format.Brush.Visible := True;
end;
```

## Detail Grid Formatting

Apply formatting to detail grids:

```delphi theme={null}
procedure TForm1.DetailGridCreated(const Sender, NewGroup: TRowGroup);
begin
  // Background
  NewGroup.Rows.Back.Brush.Color := TAlphaColors.Aliceblue;
  NewGroup.Rows.Back.Brush.Visible := True;
  
  // Alternate rows
  NewGroup.Rows.Alternate.Visible := True;
  NewGroup.Rows.Alternate.Brush.Color := TAlphaColors.Lightcyan;
  NewGroup.Rows.Alternate.Brush.Visible := True;
  
  // Font
  NewGroup.Cells.Format.Font.Color := TAlphaColors.Navy;
  NewGroup.Cells.Format.Font.Size := 9;
  
  // Header
  NewGroup.Header.Format.Brush.Color := TAlphaColors.Steelblue;
  NewGroup.Header.Format.Brush.Visible := True;
  NewGroup.Header.Format.Font.Color := TAlphaColors.White;
end;
```

## Detail Grid Selection

Handle selection in detail grids:

```delphi theme={null}
procedure TForm1.DetailGridCreated(const Sender, NewGroup: TRowGroup);
begin
  // Enable selection in detail grid
  NewGroup.Selected.Format.Brush.Color := TAlphaColors.Yellow;
  NewGroup.Selected.Format.Brush.Visible := True;
  
  // Handle selection changes
  NewGroup.OnChangedSelected := DetailSelectionChanged;
end;

procedure TForm1.DetailSelectionChanged(Sender: TObject);
var
  Group: TRowGroup;
begin
  Group := TRowGroup(Sender);
  ShowMessage('Selected row in detail: ' + IntToStr(Group.Selected.Row));
end;
```

## Children Property

Access expanded detail grids:

```delphi theme={null}
// Access children of a row
var
  ChildGroup: TRowGroup;
begin
  if TeeGrid1.Grid.Current.Rows.Children.Count > 0 then
  begin
    ChildGroup := TRowGroup(TeeGrid1.Grid.Current.Rows.Children.Row[0]);
    ShowMessage('Child grid has ' + IntToStr(ChildGroup.Data.Count) + ' rows');
  end;
end;
```

## Remove All Detail Grids

```delphi theme={null}
// Remove all expanded detail grids
TeeGrid1.Grid.Current.Rows.Children.Clear;

// Remove expander from column
if TeeGrid1.Columns.Count > 0 then
  TeeGrid1.Columns[0].Render := nil;
```

## Enable/Disable Master-Detail

```delphi theme={null}
procedure TForm1.CheckBoxEnabledChange(Sender: TObject);
var
  Expander: TExpanderRender;
begin
  if CheckBox1.Checked then
  begin
    // Enable
    Expander := TeeGrid1.Grid.Current.NewExpander;
    Expander.OnGetData := GetOrdersData;
    Expander.AlwaysExpand := True;
    
    if TeeGrid1.Columns.Count > 0 then
      TeeGrid1.Columns[0].Render := Expander;
  end
  else
  begin
    // Disable
    TeeGrid1.Grid.Current.Rows.Children.Clear;
    
    if TeeGrid1.Columns.Count > 0 then
      TeeGrid1.Columns[0].Render := nil;
  end;
end;
```

## Performance Tips

For large hierarchies:

```delphi theme={null}
// Use AlwaysExpand := True to defer data loading
Expander.AlwaysExpand := True;

// Load data only when expanded
procedure TForm1.GetOrdersData(const Sender: TExpanderRender;
  const ARow: Integer; out AData: TObject);
begin
  // Data is loaded on-demand when row is expanded
  AData := LoadOrdersForCustomer(ARow);
end;

// Limit expansion levels
var
  ExpansionLevel: Integer;

procedure TForm1.DetailGridCreated(const Sender, NewGroup: TRowGroup);
begin
  Inc(ExpansionLevel);
  
  // Only allow 2 levels deep
  if ExpansionLevel < 2 then
    SetupExpander(NewGroup, GetNextLevel)
  else
    // No more expansion
    NewGroup.OnNewDetail := nil;
end;
```

## Best Practices

* Use `AlwaysExpand := True` for dynamic data where you don't know row count in advance
* Set `OwnsData := True` on returned data objects so they're freed automatically
* Use `OnNewDetail` to customize appearance of detail grids
* Limit nesting levels (3-4 max) for usability
* Apply distinct colors to each level for visual hierarchy
* Use database queries with parameters for efficient master-detail
* Consider pagination for large detail sets
* Provide "Expand All" / "Collapse All" buttons for user convenience