> ## 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.

# TVirtualDBData

> Virtual data adapter for linking TDataSet or TDataSource to TeeGrid

## Overview

`TVirtualDBData` is a virtual data class that links TDataSet or TDataSource fields to a TeeGrid. It provides automatic integration with database components, allowing seamless display and editing of database records.

<Note>
  Setting the TeeGrid `DataSource` property to a TDataSet or TDataSource component will automatically create a `TVirtualDBData` object.
</Note>

## Usage

### Automatic Creation

The simplest way to use `TVirtualDBData` is to assign a dataset or data source directly to the grid:

```pascal theme={null}
// Using TDataSet
TeeGrid1.DataSource := FDMemTable1;

// Using TDataSource
TeeGrid1.DataSource := DataSource2;
```

### Manual Creation

You can also manually create and configure a `TVirtualDBData` instance:

```pascal theme={null}
uses Tee.GridData.DB;

// From TDataSource
TeeGrid1.Data := TVirtualDBData.From(DataSource1);

// From TDataSet
TeeGrid1.Data := TVirtualDBData.From(MyDataSet1);
```

## Types

### TVirtualFetchMode

Controls how records are fetched from the dataset:

* `Automatic` - Automatically determines fetch strategy based on dataset characteristics
* `All` - Fetches all records at once
* `Partial` - Fetches records on-demand (virtual mode)

## Properties

<ResponseField name="DataSet" type="TDataSet" readonly>
  Provides read-only access to the underlying TDataSet being displayed in the grid.

  ```pascal theme={null}
  var
    RecordCount: Integer;
  begin
    if Assigned(TVirtualDBData(TeeGrid1.Data).DataSet) then
      RecordCount := TVirtualDBData(TeeGrid1.Data).DataSet.RecordCount;
  end;
  ```
</ResponseField>

<ResponseField name="FetchMode" type="TVirtualFetchMode" default="Automatic">
  Controls the record fetching strategy. Set to `All` for smaller datasets or `Partial` for large datasets to improve performance.

  ```pascal theme={null}
  var
    DBData: TVirtualDBData;
  begin
    DBData := TVirtualDBData.From(FDQuery1);
    DBData.FetchMode := TVirtualFetchMode.Partial; // Virtual mode for large datasets
    TeeGrid1.Data := DBData;
  end;
  ```
</ResponseField>

<ResponseField name="OwnsData" type="Boolean">
  Determines whether the TVirtualDBData instance owns and will free the associated dataset. Set to `True` if you want the data adapter to manage the dataset's lifetime.

  ```pascal theme={null}
  var
    DBData: TVirtualDBData;
  begin
    DBData := TVirtualDBData.From(MyDataSet);
    DBData.OwnsData := True; // TVirtualDBData will free MyDataSet
    TeeGrid1.Data := DBData;
  end;
  ```
</ResponseField>

## Methods

### Class Methods

<ResponseField name="From" type="class function">
  Creates a TVirtualData instance from a TComponent (TDataSet or TDataSource).

  **Signature:**

  ```pascal theme={null}
  class function From(const ASource: TComponent): TVirtualData; override;
  ```

  **Parameters:**

  * `ASource` - A TDataSet or TDataSource component

  **Returns:**
  A new TVirtualDBData instance configured for the given data source.

  **Example:**

  ```pascal theme={null}
  uses Tee.GridData.DB;

  var
    GridData: TVirtualData;
  begin
    GridData := TVirtualDBData.From(FDQuery1);
    TeeGrid1.Data := GridData;
  end;
  ```
</ResponseField>

<ResponseField name="LinkTo" type="class procedure">
  Links a TeeGrid column to a specific TField from the dataset.

  **Signature:**

  ```pascal theme={null}
  class procedure LinkTo(const AColumn: TColumn; const AField: TField); static;
  ```

  **Parameters:**

  * `AColumn` - The TColumn to link
  * `AField` - The TField to link to the column

  **Example:**

  ```pascal theme={null}
  var
    Col: TColumn;
  begin
    Col := TeeGrid1.Columns.Add;
    TVirtualDBData.LinkTo(Col, MyDataSet.FieldByName('CustomerName'));
  end;
  ```
</ResponseField>

### Instance Methods

<ResponseField name="AddColumns" type="procedure">
  Automatically adds columns to the grid based on the dataset fields.

  **Signature:**

  ```pascal theme={null}
  procedure AddColumns(const AColumns: TColumns); override;
  ```

  **Parameters:**

  * `AColumns` - The columns collection to populate

  **Example:**

  ```pascal theme={null}
  var
    DBData: TVirtualDBData;
  begin
    DBData := TVirtualDBData.From(FDQuery1);
    TeeGrid1.Data := DBData;
    DBData.AddColumns(TeeGrid1.Columns); // Manually add columns
  end;
  ```
</ResponseField>

<ResponseField name="AsFloat" type="function">
  Retrieves the floating-point value of a cell.

  **Signature:**

  ```pascal theme={null}
  function AsFloat(const AColumn: TColumn; const ARow: Integer): TFloat; override;
  ```

  **Parameters:**

  * `AColumn` - The column to read from
  * `ARow` - The row index

  **Returns:**
  The cell value as a floating-point number.
</ResponseField>

<ResponseField name="AsString" type="function">
  Retrieves the string representation of a cell value.

  **Signature:**

  ```pascal theme={null}
  function AsString(const AColumn: TColumn; const ARow: Integer): String; override;
  ```

  **Parameters:**

  * `AColumn` - The column to read from
  * `ARow` - The row index

  **Returns:**
  The cell value as a string.
</ResponseField>

<ResponseField name="Count" type="function">
  Returns the total number of rows (records) in the dataset.

  **Signature:**

  ```pascal theme={null}
  function Count: Integer; override;
  ```

  **Returns:**
  The number of records in the dataset.
</ResponseField>

<ResponseField name="DataType" type="function">
  Returns the RTTI type information for a column's data type.

  **Signature:**

  ```pascal theme={null}
  function DataType(const AColumn: TColumn): PTypeInfo; override;
  ```

  **Parameters:**

  * `AColumn` - The column to query

  **Returns:**
  Pointer to the type information for the column's field type.
</ResponseField>

<ResponseField name="Load" type="procedure">
  Loads or reloads the grid columns from the dataset.

  **Signature:**

  ```pascal theme={null}
  procedure Load(const AColumns: TColumns); override;
  ```

  **Parameters:**

  * `AColumns` - The columns collection to load into
</ResponseField>

<ResponseField name="ReadOnly" type="function">
  Determines if a column is read-only based on the field properties.

  **Signature:**

  ```pascal theme={null}
  function ReadOnly(const AColumn: TColumn): Boolean; override;
  ```

  **Parameters:**

  * `AColumn` - The column to check

  **Returns:**
  `True` if the column's field is read-only, `False` otherwise.
</ResponseField>

<ResponseField name="SetValue" type="procedure">
  Sets a cell value, updating the underlying dataset field.

  **Signature:**

  ```pascal theme={null}
  procedure SetValue(const AColumn: TColumn; const ARow: Integer; const AText: String); override;
  ```

  **Parameters:**

  * `AColumn` - The column to update
  * `ARow` - The row index
  * `AText` - The new value as a string

  **Example:**

  ```pascal theme={null}
  var
    DBData: TVirtualDBData;
  begin
    DBData := TVirtualDBData(TeeGrid1.Data);
    DBData.SetValue(TeeGrid1.Columns[0], 5, 'New Value');
  end;
  ```
</ResponseField>

<ResponseField name="AutoWidth" type="function">
  Calculates the optimal column width based on the data and painter.

  **Signature:**

  ```pascal theme={null}
  function AutoWidth(const APainter: TPainter; const AColumn: TColumn): Single; override;
  ```

  **Parameters:**

  * `APainter` - The painter used for measuring text
  * `AColumn` - The column to measure

  **Returns:**
  The calculated optimal width in pixels.
</ResponseField>

<ResponseField name="EditMode" type="procedure">
  Called when the grid enters or exits edit mode.

  **Signature:**

  ```pascal theme={null}
  procedure EditMode(const AMode: TEditMode); override;
  ```

  **Parameters:**

  * `AMode` - The edit mode state
</ResponseField>

<ResponseField name="Refresh" type="procedure">
  Refreshes the grid data from the dataset.

  **Signature:**

  ```pascal theme={null}
  procedure Refresh; override;
  ```

  **Example:**

  ```pascal theme={null}
  var
    DBData: TVirtualDBData;
  begin
    DBData := TVirtualDBData(TeeGrid1.Data);
    DBData.Refresh; // Reload data from dataset
  end;
  ```
</ResponseField>

## Complete Examples

### Basic Database Grid

```pascal theme={null}
uses
  VCLTee.Grid, Tee.GridData.DB, FireDAC.Comp.Client;

procedure TForm1.FormCreate(Sender: TObject);
begin
  // Automatic - just assign the dataset
  TeeGrid1.DataSource := FDQuery1;
end;
```

### Advanced Configuration

```pascal theme={null}
uses
  VCLTee.Grid, Tee.GridData.DB, FireDAC.Comp.Client;

procedure TForm1.SetupGrid;
var
  DBData: TVirtualDBData;
begin
  // Create data adapter
  DBData := TVirtualDBData.From(FDQuery1);
  
  // Configure for large dataset
  DBData.FetchMode := TVirtualFetchMode.Partial;
  
  // Assign to grid
  TeeGrid1.Data := DBData;
  
  // Customize appearance
  TeeGrid1.Columns[0].Width := 200;
  TeeGrid1.Columns[1].Visible := False;
end;
```

### Master-Detail Grids

```pascal theme={null}
uses
  VCLTee.Grid, Tee.GridData.DB;

procedure TForm1.SetupMasterDetail;
begin
  // Master grid
  MasterGrid.DataSource := MasterDataSet;
  
  // Detail grid
  DetailGrid.DataSource := DetailDataSet;
  
  // Link via dataset relationship
  DetailDataSet.MasterSource := MasterDataSource;
  DetailDataSet.MasterFields := 'CustomerID';
end;
```

### Custom Field Linking

```pascal theme={null}
uses
  VCLTee.Grid, Tee.GridData.DB, Tee.Grid.Columns;

procedure TForm1.CreateCustomColumns;
var
  DBData: TVirtualDBData;
  Col: TColumn;
begin
  DBData := TVirtualDBData.From(MyDataSet);
  TeeGrid1.Data := DBData;
  
  // Manually create and link columns
  TeeGrid1.Columns.Clear;
  
  Col := TeeGrid1.Columns.Add;
  Col.Text := 'Customer';
  TVirtualDBData.LinkTo(Col, MyDataSet.FieldByName('CustomerName'));
  
  Col := TeeGrid1.Columns.Add;
  Col.Text := 'Total';
  TVirtualDBData.LinkTo(Col, MyDataSet.FieldByName('OrderTotal'));
end;
```

## See Also

* [TVirtualData](/api/virtualdata) - Base class for all data adapters
* [TDataSet Binding](/data/datasets) - Guide to working with datasets
* [Database Grid Examples](/examples/database-grid) - Complete examples