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一、概述
在用Delphi編寫數(shù)據(jù)庫程序時(shí)，經(jīng)常涉及到數(shù)據(jù)的導(dǎo)入和導(dǎo)出操作，如：將大型數(shù)據(jù)庫中的數(shù)據(jù)存儲(chǔ)為便攜文件，以便于出外閱讀；將存儲(chǔ)在文件中的數(shù)據(jù)信息，導(dǎo)入到另外的數(shù)據(jù)庫中；而且，通過將數(shù)據(jù)庫中的數(shù)據(jù)存儲(chǔ)為數(shù)據(jù)文件，更便于程序內(nèi)部和程序間交換數(shù)據(jù)，避免通過內(nèi)存交換數(shù)據(jù)的煩瑣步驟，例如在筆者編寫的通用報(bào)表程序中即以該控件作為數(shù)據(jù)信息傳遞的載體。
二、基本思路
作為數(shù)據(jù)報(bào)存儲(chǔ)控件，應(yīng)能夠存儲(chǔ)和讀入數(shù)據(jù)集的基本信息（如：字段名，字段的顯示名稱，字段的數(shù)據(jù)類型，記錄數(shù)，字段數(shù)，指定記錄指定字段的當(dāng)前值等），應(yīng)能夠提供較好的封裝特性，以便于使用。
基于此，筆者利用Delphi5.0面向?qū)ο蟮奶攸c(diǎn)，設(shè)計(jì)開發(fā)了數(shù)據(jù)報(bào)存儲(chǔ)控件。
三、實(shí)現(xiàn)方法
編寫如下代碼單元：
unit IbDbFile;
interface
Uses Windows, SysUtils, Classes, Forms, Db, DbTables, Dialogs;
Const
Flag = '數(shù)據(jù)報(bào)-吉星軟件工作室';
Type
TDsException = Class(Exception);
TIbStorage = class(TComponent)
private
FRptTitle: string; //存儲(chǔ)數(shù)據(jù)報(bào)說明
FPageHead: string; //頁頭說明
FPageFoot: string; //爺腳說明
FFieldNames: TStrings; //字段名表
FStreamIndex: TStrings; //字段索引
FStream: TStream; //存儲(chǔ)字段內(nèi)容的流
FFieldCount: Integer; //字段數(shù)
FRecordCount: Integer; //記錄數(shù)
FOpenFlag: Boolean; //流是否創(chuàng)建標(biāo)志
protected
procedure Reset; //復(fù)位---清空流的內(nèi)容
procedure SaveHead(ADataSet: TDataSet; Fp: TStream); //存儲(chǔ)報(bào)表頭信息
procedure LoadTableToStream(ADataSet: TDataSet); //存儲(chǔ)記錄數(shù)據(jù)
procedure IndexFields(ADataSet: TDataSet); //將數(shù)據(jù)集的字段名保存到列表中
procedure GetHead(Fp: TFileStream); //保存報(bào)表頭信息
procedure GetIndex(Fp: TFileStream); //建立記錄流索引
procedure GetFieldNames(Fp: TFileStream); //從流中讀入字段名表
function GetFieldName(AIndex: Integer): string; //取得字段名稱
function GetFieldDataType(AIndex: Integer): TFieldType;
function GetDisplayLabel(AIndex: Integer): string; //取得字段顯示名稱
procedure SaveFieldToStream(AStream: TStream; AField: TField); //將字段存入流中
function GetFieldValue(ARecordNo, FieldNo: Integer): string; //字段的內(nèi)容
public
Constructor Create(AOwner: TComponent);
Destructor Destroy; override;
procedure Open; //創(chuàng)建流以準(zhǔn)備存儲(chǔ)數(shù)據(jù)
procedure SaveToFile(ADataSet: TDataSet; AFileName: string); //存儲(chǔ)方法
procedure LoadFromFile(AFileName: string); //裝入數(shù)據(jù)
procedure FieldStream(ARecordNo, FieldNo: Integer; var AStream: TStream);
property FieldNames[Index: Integer]: string read GetFieldName; //字段名
property FieldDataTypes[Index: Integer]: TFieldType read GetFieldDataType;
property FieldDisplayLabels[Index: Integer]: string read GetDisplayLabel;
property Fields[RecNo, FieldIndex: Integer]: string read GetFieldValue;
//property FieldStreams[RecNo, FieldIndex: Integer]: TStream read GetFieldStream;
property RecordCount: Integer read FRecordCount write FRecordCount;
property FieldCount: Integer read FFieldCount write FFieldCount;
published
property RptTitle: string read FRptTitle write FRptTitle;
property PageHead: string read FPageHead write FPageHead;
property PageFoot: string read FPageFoot write FPageFoot;
end;
function ReadAChar(AStream: TStream): Char;
function ReadAStr(AStream: TStream): string;
function ReadBStr(AStream: TStream; Size: Integer): string;
function ReadAInteger(AStream: TStream): Integer;
procedure WriteAStr(AStream: TStream; AStr: string);
procedure WriteBStr(AStream: TStream; AStr: string);
procedure WriteAInteger(AStream: TStream; AInteger: Integer);
procedure Register;
implementation
procedure Register;
begin
RegisterComponents('Data Access', [TIbStorage]);
end;
function ReadAChar(AStream: TStream): Char;
Var
AChar: Char;
begin
AStream.Read(AChar, 1);
Result := AChar;
end;
function ReadAStr(AStream: TStream): string;
var
Str: String;
C : Char;
begin
Str := '';
C := ReadAChar(AStream);
While C <> #0 do
begin
Str := Str + C;
C := ReadAChar(AStream);
end;
Result := Str;
end;
function ReadBStr(AStream: TStream; Size: Integer): string;
var
Str: String;
C : Char;
I : Integer;
begin
Str := '';
For I := 1 to Size do
begin
C := ReadAChar(AStream);
Str := Str + C;
end;
Result := Str;
end;
function ReadAInteger(AStream: TStream): Integer;
var
Str: String;
C : Char;
begin
Result := MaxInt;
Str := '';
C := ReadAChar(AStream);
While C <> #0 do
begin
Str := Str + C;
C := ReadAChar(AStream);
end;
try
Result := StrToInt(Str);
except
Application.MessageBox(' 當(dāng)前字符串無法轉(zhuǎn)換為整數(shù)!', '錯(cuò)誤',
Mb_Ok + Mb_IconError);
end;
end;
procedure WriteAStr(AStream: TStream; AStr: string);
begin
AStream.Write(Pointer(AStr)^, Length(AStr) + 1);
end;
procedure WriteBStr(AStream: TStream; AStr: string);
begin
AStream.Write(Pointer(AStr)^, Length(AStr));
end;
procedure WriteAInteger(AStream: TStream; AInteger: Integer);
var
S : string;
begin
S := IntToStr(AInteger);
WriteAstr(AStream, S);
end;
Constructor TIbStorage.Create(AOwner: TComponent);
begin
inherited Create(AOwner);
FOpenFlag := False; //確定流是否創(chuàng)建的標(biāo)志
end;
Destructor TIbStorage.Destroy;
begin
if FOpenFlag then
begin
FStream.Free;
FStreamIndex.Free;
FFieldNames.Free;
end;
inherited Destroy;
end;
procedure TIbStorage.Open;
begin
FOpenFlag := True;
FStream := TMemoryStream.Create;
FStreamIndex := TStringList.Create;
FFieldNames := TStringList.Create;
Reset;
end;
procedure TIbStorage.Reset; //復(fù)位
begin
if FOpenFlag then
begin
FFieldNames.Clear;
FStreamIndex.Clear;
FStream.Size := 0;
FRptTitle := '';
FPageHead := '';
FPageFoot := '';
FFieldCount := 0;
FRecordCount := 0;
end;
end;
//-------保存數(shù)據(jù)部分
procedure TIbStorage.SaveToFile(ADataSet: TDataSet; AFileName: string);
var
Fp: TFileStream;
I : Integer;
Ch: Char;
T1, T2: TDateTime;
Str: string;
begin
if Not FOpenFlag then
begin
showmessage(' 對(duì)象沒有打開');
Exit;
end;
try
if FileExists(AFileName) then DeleteFile(AFileName);
Fp := TFileStream.Create(AFileName, fmCreate);
Reset;
SaveHead(ADataSet, Fp); //保存頭部信息---附加說明
IndexFields(ADataSet); //將數(shù)據(jù)集的字段信息保存到FFieldName
LoadTableToStream(ADataSet); //保存數(shù)據(jù)集的數(shù)據(jù)信息
WriteAStr(Fp, FFieldNames.Text); //存儲(chǔ)字段名信息
Ch := '@';
Fp.Write(Ch, 1);
WriteAStr(Fp, FStreamIndex.Text); //存儲(chǔ)字段索引列表
Ch := '@';
Fp.Write(Ch, 1);
Fp.CopyFrom(FStream, 0);
finally
Fp.Free;
end;
end;
procedure TIbStorage.SaveHead(ADataSet: TDataSet; Fp: TStream);
Var
I : Integer;
Ch: Char;
begin
if Not ADataSet.Active then ADataSet.Active := True;
WriteAStr(Fp, Flag);
WriteAStr(Fp, FRptTitle);
WriteAStr(Fp, FPageHead);
WriteAStr(Fp, FPageFoot);
FFieldCount := ADataSet.Fields.Count;
FRecordCount := ADataSet.RecordCount;
WriteAStr(Fp, IntToStr(ADataSet.Fields.Count));
WriteAStr(Fp, IntToStr(ADataSet.RecordCount));
Ch := '@';
Fp.Write(Ch, 1);
end;
procedure TIbStorage.IndexFields(ADataSet: TDataSet);
var
I : Integer;
AField: TField;
begin
For I := 0 to ADataSet.Fields.Count - 1 do
begin
AField := ADataSet.Fields[I];
//不用FFieldNames.Values[AField.FieldName] := AField.DisplayLabel;是考慮效率
FFieldNames.Add(AField.FieldName + '=' + AField.DisplayLabel);
FFieldNames.Add(AField.FieldName + 'DataType=' + IntToStr(Ord(AField.DataType)));
end;
end;
procedure TIbStorage.LoadTableToStream(ADataSet: TDataSet);
var
No: Integer;
I, J, Size: Integer;
Tmp, Id, Str : string; //id=string(RecNO) + string(FieldNo)
Len: Integer;
Ch : Char;
BlobStream: TBlobStream;
begin
if Not FOpenFlag then
begin
showmessage(' 對(duì)象沒有打開');
Exit;
end;
try
ADataSet.DisableControls;
ADataSet.First;
No := 0;
FStreamIndex.Clear;
FStream.Size := 0;
While Not ADataSet.Eof do
begin
No := No + 1;
For J := 0 to ADataSet.Fields.Count - 1 do
begin
Id := Inttostr(NO) + '_' + IntToStr(J);
//建立流的位置的索引, 索引指向: Size#0Content
FStreamIndex.Add(Id + '=' + IntToStr(FStream.Position));
//存儲(chǔ)字段信息到流中
SaveFieldToStream(FStream, ADataSet.Fields[J]);
end;
ADataSet.Next;
end;
finally
ADataSet.EnableControls;
end;
end;
//如果一個(gè)字段的當(dāng)前內(nèi)容為空或者BlobSize<=0,則只寫入字段大小為0, 不寫入內(nèi)容
procedure TIbStorage.SaveFieldToStream(AStream: TStream; AField: TField);
var
Size: Integer;
Ch: Char;
XF: TStream;
Str: string;
begin
if AField.IsBlob then
begin
//如何把一個(gè)TBlobField字段的內(nèi)容存儲(chǔ)為流
Xf := TBlobStream.Create(TBlobField(AField), bmread);
try
if Xf.Size > 0 then
begin
Size := Xf.Size;
WriteAInteger(AStream, Size);
AStream.CopyFrom(Xf, Xf.Size);
end
else
WriteAInteger(AStream, 0);
finally
XF.Free;
end;
end
else
begin
Str := AField.AsString;
Size := Length(Str);
WriteAInteger(AStream, Size);
if Size <> 0 then
AStream.Write(Pointer(Str)^, Size);
//WriteAstr(AStream, Str);
end;
Ch := '@';
AStream.Write(Ch, 1);
end;
//------------Load Data
procedure TIbStorage.LoadFromFile(AFileName: string);
var
Fp: TFileStream;
Check: string;
begin
Reset;
try
if Not FileExists(AFileName) then
begin
showmessage(' 文件不存在:' + AFileName);
Exit;
end;
Fp := TFileStream.Create(AFileName, fmOpenRead);
Check := ReadAStr(Fp);
if Check <> Flag then
begin
Application.MessageBox(' 非法文件格式', '錯(cuò)誤', Mb_Ok + Mb_IconError);
Exit;
end;
GetHead(Fp);
GetFieldNames(Fp);
GetIndex(Fp);
FStream.CopyFrom(Fp, Fp.Size-Fp.Position);
finally
Fp.Free;
end;
end;
procedure TIbStorage.GetHead(Fp: TFileStream);
begin
FRptTitle := ReadAStr(Fp);
FPageHead := ReadAstr(Fp);
FPageFoot := ReadAstr(Fp);
FFieldCount := ReadAInteger(Fp);
FRecordCount := ReadAInteger(Fp);
if ReadAChar(Fp) <> '@' then showmessage('GetHead File Error');
end;
procedure TIbStorage.GetFieldNames(Fp: TFileStream);
var
Ch: Char;
Str: string;
begin
Str := '';
Str := ReadAStr(Fp);
FFieldNames.CommaText := Str;
Ch := ReadAChar(Fp);
if Ch <> '@' then Showmessage('When get fieldnames Error');
end;
procedure TIbStorage.GetIndex(Fp: TFileStream);
var
Ch: Char;
Str: string;
begin
Str := '';
Str := ReadAStr(Fp);
FStreamIndex.CommaText := Str;
Ch := ReadAChar(Fp);
if Ch <> '@' then Showmessage('When Get Field Position Index Error');
end;
//---------Read Field's Value Part
function TIbStorage.GetFieldValue(ARecordNo, FieldNo: Integer): string;
var
Id, T : string;
Pos: Integer;
Len, I : Integer;
Er: Boolean;
begin
Result := '';
Er := False;
if ARecordNo > FRecordCount then
Er := true; //ARecordNo := FRecordCount;
if ARecordNo < 1 then
Er := True; // ARecordNo := 1;
if FieldNo >= FFieldCount then
Er := True; // FieldNo := FFieldCount - 1;
if FieldNo < 0 then
Er := True; //FieldNo := 0;
if Er then
begin
Showmessage('記錄號(hào)或者字段標(biāo)號(hào)越界');
Exit;
end;
if FFieldCount = 0 then Exit;
Id := Inttostr(ARecordNO) + '_' + IntToStr(FieldNo);
Pos := StrToInt(FStreamIndex.Values[Id]);
FStream.Position := Pos;
//取得字段內(nèi)容的長(zhǎng)度
Len := ReadAInteger(FStream);
if Len > 0 then
Result := ReadBStr(FStream, Len);
if ReadAChar(FStream) <> '@' then
Showmessage('When Read Field, Find Save Format Error');
end;
procedure TIbStorage.FieldStream(ARecordNo, FieldNo: Integer; var AStream: TStream);
var
Id, T : string;
Pos: Integer;
Len, I : Integer;
Er: Boolean;
begin
Er := False;
if ARecordNo > FRecordCount then
Er := true; //ARecordNo := FRecordCount;
if ARecordNo < 1 then
Er := True; // ARecordNo := 1;
if FieldNo >= FFieldCount then
Er := True; // FieldNo := FFieldCount - 1;
if FieldNo < 0 then
Er := True; //FieldNo := 0;
if Er then
begin
TDsException.Create('GetFieldValue函數(shù)索引下標(biāo)越界');
Exit;
end;
if FFieldCount = 0 then Exit;
Id := Inttostr(ARecordNO) + IntToStr(FieldNo);
Pos := StrToInt(FStreamIndex.Values[Id]);
FStream.Position := Pos;
Len := ReadAInteger(FStream);
AStream.CopyFrom(FStream, Len);
end;
function TIbStorage.GetFieldName(AIndex: Integer): string; //取得字段名稱
begin
//存儲(chǔ)的字段和數(shù)據(jù)類型各占一半
if ((AIndex < 0) or (AIndex >= FFieldNames.Count div 2)) then
Application.MessageBox(' 取字段名索引越界', '程序 錯(cuò)誤',
Mb_Ok + Mb_IconError)
else
Result := FFieldNames.Names[AIndex*2];
end;
function TIbStorage.GetFieldDataType(AIndex: Integer): TFieldType; //取得字段名稱
begin
//存儲(chǔ)的字段和數(shù)據(jù)類型各占一半
if ((AIndex < 0) or (AIndex >= FFieldNames.Count div 2)) then
Application.MessageBox(' 取字段數(shù)據(jù)類型索引越界', '程序 錯(cuò)誤',
Mb_Ok + Mb_IconError)
else
Result := TFieldType(StrToInt(FFieldNames.Values[FFieldNames.Names[AIndex*2+1]]));
end;
function TIbStorage.GetDisplayLabel(AIndex: Integer): string; //取得字段顯示名稱
begin
if ((AIndex < 0) or (AIndex >= FFieldNames.Count)) then
Application.MessageBox(' 取字段名索引越界', '程序 錯(cuò)誤',
Mb_Ok + Mb_IconError)
else
Result := FFieldNames.Values[GetFieldName(AIndex)];
end;
end.
通過測(cè)試，該控件對(duì)Ttable,Tquery, TaodTable, TadoQuery, TibTable, TibQuery等常用的數(shù)據(jù)集控件等都能較好的支持，并且具有較好的效率（測(cè)試：1100條人事記錄，23個(gè)字段存儲(chǔ)為文件約用時(shí)2秒鐘）。
四、控件的基本使用方法
1．存儲(chǔ)數(shù)據(jù)集中的數(shù)據(jù)到文件
IbStorage1.Open; //創(chuàng)建存儲(chǔ)流
IbStorage1.SaveToFile(AdataSet, Afilename);
2．從文件中讀出數(shù)據(jù)信息
IbStorage1.Open;
IbStorage1.LoadFromFile(AfileName);
3．對(duì)數(shù)據(jù)報(bào)存儲(chǔ)控件中數(shù)據(jù)的訪問
Value := IbStorage1.Fields[ArecNo, AfieldNo]; //字符串類型
其它略。
五、結(jié)束語
通過編寫此數(shù)據(jù)報(bào)存儲(chǔ)控件，較好地解決了數(shù)據(jù)庫程序中數(shù)據(jù)的存儲(chǔ)和交換問題，為數(shù)據(jù)庫程序的開發(fā)提供了一種實(shí)用的控件。
該控件在Windows98，Delphi5開發(fā)環(huán)境下調(diào)試通過。
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