DELPHI开发2层C/S数据库应用程序，许多人通过ADOQUERY或ADOTABLE直接操作数据库，其实这种方法虽然最为直接，但有其缺点：如果以后要将程序升级为3层C/S会非常困难。而通过像下面的通用数据操作方法，像开发3层C/S一样地开发2层C/S程序，通过ADOQUERY或ADOTABLE获取数据，通过DATASETPROVIDER转换数据格式为OLEVARIANT，通过CLIENTDATASET内存数据集再同客户端显示控件关联，则所有操作数据的方法高度集中统一，以后要升级为多层会非常容易。这就是间接所带来的高度灵活。
ADO不能像FIREDAC和UNIDAC一样提交联表查询的CLIENTDATASET.DELTA，这在保存类似“单据”的数据的时候很不方便，需要间接一下然后才能提交。
FIREDAC和UNIDAC虽然默认也不支持，但只要设置属性就能获得支持。
其中FIREDAC的设置：UpdateOptions.CheckReadOnly:=False
其中的原由：A表联接B表查询，CLIENTDATASET中的字段既有A表的也有B表的，试图将CLIENTDATASET.delta提交给A表，CLIENTDATASET.delta将B表的字段值改变也一块打包了，而B表的字段的readonly:=true，试图提交只读字段会报错。
unit untDB;
interface
uses
System.SysUtils, System.Classes, Data.DB, Data.Win.ADODB, Datasnap.Provider,
System.Variants, Vcl.Forms;
type
TfrmDB = class(TDataModule)
ADOConnection1: TADOConnection;
qryQuery: TADOQuery;
DataSetProvider1: TDataSetProvider;
qryExecute: TADOQuery;
procedure DataModuleCreate(Sender: TObject);
procedure qryQueryBeforeOpen(DataSet: TDataSet);
procedure qryQueryAfterOpen(DataSet: TDataSet);
private
{ Private declarations }
procedure connectDB;
public
{ Public declarations }
function querySQL(const sql: string): OleVariant;
function executeSQL(const sql: string): Boolean;
function saveData(const tableName: string; delta: OleVariant): Boolean;
function SaveDatas(tableNames, deltas: OleVariant;
tableCount: Integer): Boolean;
end;
var
frmDB: TfrmDB;
implementation
{ %CLASSGROUP ‘Vcl.Controls.TControl‘ }
uses UnitWait;
{$R *.dfm}
{ TfrmDB }
procedure TfrmDB.connectDB;
begin
ADOConnection1.Close;
ADOConnection1.ConnectionString := ‘FILE NAME=‘ +
ExtractFilePath(Application.ExeName) + ‘db.udl‘;
try
ADOConnection1.Connected := True;
except
on E: Exception do
raise Exception.Create(E.Message);
end;
end;
procedure TfrmDB.DataModuleCreate(Sender: TObject);
begin
connectDB;
end;
function TfrmDB.executeSQL(const sql: string): Boolean;
begin
Result := False;
if sql = ‘‘ then
Exit;
qryExecute.Close;
qryExecute.sql.Clear;
qryExecute.sql.Text := sql;
Result := qryExecute.ExecSQL > 0;
end;
procedure TfrmDB.qryQueryAfterOpen(DataSet: TDataSet);
begin
FormWait.Close;
FormWait.Free;
end;
procedure TfrmDB.qryQueryBeforeOpen(DataSet: TDataSet);
begin
FormWait := TFormWait.Create(Application);
FormWait.Show;
FormWait.Update;
end;
function TfrmDB.querySQL(const sql: string): OleVariant;
begin
Result := null;
if sql = ‘‘ then
Exit;
qryQuery.Close;
qryQuery.sql.Clear;
qryQuery.sql.Text := sql;
qryQuery.Open;
Result := DataSetProvider1.Data;
end;
function TfrmDB.saveData(const tableName: string; delta: OleVariant): Boolean;
var
errCnt: Integer;
begin
Result := False;
if (tableName = ‘‘) or VarIsNull(delta) then
Exit;
qryQuery.Close;
qryQuery.sql.Clear;
qryQuery.sql.Text := ‘select * from ‘ + tableName + ‘ where 1=2‘;
qryQuery.Open;
DataSetProvider1.ApplyUpdates(delta, 0, errCnt);
Result := errCnt = 0;
end;
function TfrmDB.SaveDatas(tableNames, deltas: OleVariant;
tableCount: Integer): Boolean;
var
i, errCnt: Integer;
begin
if not ADOConnection1.InTransaction then
ADOConnection1.BeginTrans; // 开启事务
try
for i := 0 to tableCount - 1 do
begin
qryQuery.Close;
qryQuery.sql.Clear;
qryQuery.sql.Text := ‘select * from ‘ + tableNames[i] + ‘ where 1=2‘;
qryQuery.Open;
DataSetProvider1.ApplyUpdates(deltas[i], 0, errCnt);
end;
ADOConnection1.CommitTrans; // 提交事务
Result := True;
except
ADOConnection1.RollbackTrans; // 回滚事务
Result := False;
end;
end;
end.