线程化的Delphi ADO查询

问题描述

我有一个查询代码，每次需要从数据库中获取数据时都可以调用该查询代码，并且希望将其进行线程化.不确定如何在线程中实现此功能，因此我可以重用此代码，基本上，我希望将此代码存储在线程中.我知道如何在线程中创建一个简单的数据库查询，但是想要一些我可以重用的东西.谁能指出我在哪里可以找到示例的例子，或者足够友善地提供示例?

I have a query code that I can call every time I need to fetch data from the database, and I want it to be threaded. Not sure how to implement this in a thread so I can reuse this code, basically, I want this code inside a thread. I know how to create a simple database query inside thread but want something that I can reuse. Can anyone point me to where I can find examples for this or be kind enough to provide an example?

这是我的示例数据库查询:

Here is my sample database query:

function TDBConnection.SQLOpen(const SQLStr: String): TDataSet;
var
  i: Integer
begin
  try
    Result := TADOQuery.Create(DBConnect.FDatabaseConection);
    TADOQuery(Result).Connection:=DBConnect.FDatabaseConnection;
    TADOQuery(Result).CommandTimeOut:=30;
    TADOQuery(Result).SQL.Text := SQLStr;
    TADOQuery(Result).Open;
  except

  end;
end;

这是我如何调用上述函数的示例:

And this is a sample of how I'm calling the above function:

function TDBConnection.GetUserInfo: Boolean;
var
  sqlStr: String;
  Database: TDataset;
begin
  sqlStr:= 'SELECT FIELD1, FIELD2, FIELD3 FROM TABLE1';
  try
    Dataset := SQLOpen(sqlStr);
    if not Dataset.IsEmpty then
    begin
      //pass result to StringGrid
    end;
  finally
    FreeAndNil(SQLParams);
    FreeAndNil(Dataset);
  end;
end;

推荐答案

使用带有参数信息的数组可重复使用.
每个线程都会创建一个带有自己的Connection的自己的Adodataset.
线程终止后，记录集可用于显示和编辑.
对于真正的应用程序，必须添加线程实例的处理.

For reusability using an array with parameterinformations.
Every thread creates an own Adodataset with own Connection.
Recordset can be used for displaying and editing after thread terminated.
For a real application handling of thread instances will have to be add.

unit ThreadedAdoDataset;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, DB, ADODB, Grids, DBGrids;

type

  TFieldInfoRecord = Record // as far as sometimes parametertypes can not be detected by
    DataType: TFieldType; // Ado on his own, provide all needed informations
    Name: String;
    Size: Integer;
    Value: Variant;
  End;

  TFieldInfoArray = Array of TFieldInfoRecord;

  TDBThread = Class(TThread)
    Constructor Create(Const ConnectionString, SQL: String;
      FDArray: TFieldInfoArray);
  private
    FConnectionString, FSQL: String;
    FFDArray: TFieldInfoArray;
    FRecordSet: _RecordSet;
  Protected
    Procedure Execute; override;
  public
    Property RecordSet: _RecordSet read FRecordSet;
  End;

  TForm7 = class(TForm)
    ADOConnection1: TADOConnection;
    Button1: TButton;
    ADODataSet1: TADODataSet;
    DataSource1: TDataSource;
    DBGrid1: TDBGrid;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    procedure ThreadTerminate(Sender: TObject);
    { Private-Deklarationen }
  public
    { Public-Deklarationen }
  end;

var
  Form7: TForm7;

implementation

uses ActiveX;
{$R *.dfm}

procedure TForm7.Button1Click(Sender: TObject);
var
  FDArray: TFieldInfoArray;
  I: Integer;
begin
  // prepare parameterinformations
  SetLength(FDArray, 1);
  FDArray[0].Name := 'cn';
  FDArray[0].DataType := ftString;
  FDArray[0].Size := 20;
  FDArray[0].Value := '%ue%';

  for I := 0 to 10 do // testrun with 11 threads

    With TDBThread.Create(ADOConnection1.ConnectionString,
      'select * from Composition where Componame like :cn', FDArray) do
    begin
      FreeOnTerminate := true;
      // assign the wished procedure to ba called on terminate
      OnTerminate := ThreadTerminate;
    end;

end;

procedure TForm7.ThreadTerminate(Sender: TObject);
begin
  // example of assigning the recordset of the thread for displaying and editing
  // NOTE for editing the connection of ADODataSet1 has to be fitting to the threadcall
  ADODataSet1.RecordSet := TDBThread(Sender).RecordSet;
end;

procedure TForm7.FormCreate(Sender: TObject);
begin
  ReportMemoryLeaksOnShutDown := true;
end;


{ TDBThread }

constructor TDBThread.Create(const ConnectionString, SQL: String;
  FDArray: TFieldInfoArray);
var
  I: Integer;
begin
  inherited Create(false);
  FConnectionString := ConnectionString;
  FSQL := SQL;
  SetLength(FFDArray, Length(FDArray));
  for I := 0 to High(FDArray) do
  begin
    FFDArray[I].DataType := FDArray[I].DataType;
    FFDArray[I].Size := FDArray[I].Size;
    FFDArray[I].Name := FDArray[I].Name;
    FFDArray[I].Value := FDArray[I].Value;
  end;
end;

procedure TDBThread.Execute;
var
  I: Integer;
begin
  inherited;
  CoInitialize(nil);
  try
    With TADODataSet.Create(nil) do
      try
        CommandTimeOut := 600;
        ConnectionString := FConnectionString;
        // use own connection for the dataset
        // will requite a conncetionsstring including all
        // information for loggon
        Commandtext := FSQL;
        Parameters.ParseSQL(FSQL, true); // extract parameters
        for I := Low(FFDArray) to High(FFDArray) do // set parametervalues
        begin
          Parameters.ParamByName(FFDArray[I].Name).DataType := FFDArray[I]
            .DataType;
          Parameters.ParamByName(FFDArray[I].Name).Size := FFDArray[I].Size;
          Parameters.ParamByName(FFDArray[I].Name).Value := FFDArray[I].Value;
        end;
        Open;
        FRecordSet := RecordSet; // keep recordset
      finally
        Free;
      end;
  finally
    CoUnInitialize;
  end;
end;

end.

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