DFAsyncQuery - Background Database Queries for Delphi

A thread-based asynchronous database query component for modern Delphi applications. This library allows you to execute database queries in the background without freezing the UI, making your applications more responsive.

Features

• Non-blocking UI: Execute database queries in background threads
• Thread safety: Proper synchronization and thread management
• Modern design: Optimized for recent Delphi versions (10.4+)
• Memory safety: Automatic cleanup and resource management
• Error handling: Comprehensive exception management
• Easy integration: Simple API for existing applications

Installation

1. Download or clone this repository
2. Add the DFAsyncQuery.pas unit to your project
3. Add DFAsyncQuery to your uses clause

Usage Examples

Basic Usage

procedure TForm1.SearchButtonClick(Sender: TObject);
var
  QueryThread: TDFQueryThread;
begin
  // Create and execute a query thread
  QueryThread := DFQueryManager.CreateQueryThread(
    ADOConnection1.ConnectionString,
    'SELECT * FROM Customers WHERE LastName LIKE :LastName',
    CreateParameters('LastName', '%' + edtSearch.Text + '%'),
    DBGrid1,
    ADOQuery1,
    Self
  );
  
  // The thread automatically starts and updates the UI when complete
end;

// Helper function to create parameters
function TForm1.CreateParameters(const ParamName, ParamValue: string): TParameters;
begin
  ADOQuery1.Parameters.Clear;
  ADOQuery1.Parameters.CreateParameter(ParamName, ftString, pdInput, 50, ParamValue);
  Result := ADOQuery1.Parameters;
end;

Multiple Concurrent Queries

procedure TForm1.ExecuteMultipleQueries(Sender: TObject);
begin
  // Execute first query
  DFQueryManager.CreateQueryThread(
    ADOConnection1.ConnectionString,
    'SELECT * FROM Customers',
    nil,
    DBGrid1,
    ADOQuery1,
    Self
  );
  
  // Execute second query simultaneously
  DFQueryManager.CreateQueryThread(
    ADOConnection1.ConnectionString,
    'SELECT * FROM Orders',
    nil,
    DBGrid2,
    ADOQuery2,
    Self
  );
end;

Thread Management

procedure TForm1.FormDestroy(Sender: TObject);
begin
  // Clean up any running threads when closing the form
  DFQueryManager.CleanupThreads;
end;

procedure TForm1.btnCancelQueryClick(Sender: TObject);
begin
  // Cancel all active queries
  DFQueryManager.CleanupThreads;
  
  // Show current thread count
  ShowMessage('Active Threads: ' + IntToStr(DFQueryManager.ThreadCount));
end;

API Reference

TDFQueryThread

The main thread class for executing asynchronous queries.

Properties

• ID: Unique identifier for the thread
• HasError: Whether an error occurred during execution
• ExceptionMessage: Error message if HasError is true

TDFQueryManager

Singleton manager that handles thread creation and lifecycle management.

Methods

• CreateQueryThread: Creates and starts a new query thread
• CleanupThreads: Terminates all running threads
• RemoveThread: Removes a specific thread by ID
• ThreadCount: Returns the number of active threads

Advanced Usage

Custom Error Handling

You can implement custom error handling by checking the thread's HasError property:

procedure TForm1.ExecuteQueryWithErrorHandling;
var
  QueryThread: TDFQueryThread;
begin
  QueryThread := DFQueryManager.CreateQueryThread(
    ADOConnection1.ConnectionString,
    'SELECT * FROM NonExistentTable', // This will cause an error
    nil,
    DBGrid1,
    ADOQuery1,
    Self
  );
  
  // The thread will automatically show an error dialog,
  // but you can also implement custom error tracking or logging
end;

Progress Indication

The component automatically handles cursor changes (hourglass during queries), but you can implement additional progress indication:

procedure TForm1.btnSearchClick(Sender: TObject);
begin
  // Show progress panel
  pnlProgress.Visible := True;
  
  // Execute query
  DFQueryManager.CreateQueryThread(
    ADOConnection1.ConnectionString,
    'SELECT * FROM LargeTable',
    nil,
    DBGrid1,
    ADOQuery1,
    Self
  );
  
  // You'll need to handle hiding the progress panel when the query completes
  // This could be done using a custom event or timer
end;

Requirements

• Delphi 10.4 or later
• VCL application
• ADO database components

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is licensed under the MIT License - see the LICENSE file for details.