Author: Tomas Rutkauskas
How can I save a file in an Access database. I would like to save zip files in an
Access mdb database. (OLE OBJECT Field) BLOB FIELD
Answer:
Solve 1:
Here's a unit that demonstrates getting a file to/ from a blob field:
1 unit FileToFromDB;
2
3 interface
4
5 uses
6 Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
7 StdCtrls, FileCtrl, DBCtrls, ExtCtrls, Db, DBTables, Menus;
8
9 type
10 TFrmFileToFromDB = class(TForm)
11 CbxDriveSelect: TDriveComboBox;
12 LbxDirSelect: TDirectoryListBox;
13 LbxFileSelect: TFileListBox;
14 BtnToDB: TButton;
15 DataSource1: TDataSource;
16 Table1: TTable;
17 Table1TheLongInt: TIntegerField;
18 Table1ABlobField: TBlobField;
19 Table1Bytes1: TBlobField;
20 Table1Bytes2: TBytesField;
21 Table1B32_1: TBlobField;
22 Table1B32_2: TBytesField;
23 DBNavigator1: TDBNavigator;
24 BtnFromDB: TButton;
25 Memo1: TMemo;
26 LblCopyright: TLabel;
27 procedure FormCreate(Sender: TObject);
28 procedure FormDestroy(Sender: TObject);
29 procedure BtnToDBClick(Sender: TObject);
30 procedure BtnFromDBClick(Sender: TObject);
31 procedure LbxFileSelectChange(Sender: TObject);
32 procedure DataSource1DataChange(Sender: TObject; Field: TField);
33 private
34 { Private declarations }
35 public
36 { Public declarations }
37 end;
38
39 var
40 FrmFileToFromDB: TFrmFileToFromDB;
41
42 implementation
43
44 {$R *.DFM}
45
46 procedure TFrmFileToFromDB.FormCreate(Sender: TObject);
47 begin
48 Table1.Open;
49 Memo1.Clear;
50 end;
51
52 procedure TFrmFileToFromDB.FormDestroy(Sender: TObject);
53 begin
54 Table1.Close;
55 end;
56
57 procedure TFrmFileToFromDB.BtnToDBClick(Sender: TObject);
58 var
59 curNdx: Integer;
60 f: Integer;
61 theBlobStream: TBlobStream;
62 thisFile: TFileStream;
63 begin
64 curNdx := LbxFileSelect.ItemIndex;
65 LbxFileSelect.Items.BeginUpdate;
66 try
67 for f := 0 to LbxFileSelect.Items.Count - 1 do
68 begin
69 if LbxFileSelect.Selected[f] then
70 begin
71 LbxFileSelect.ItemIndex := f;
72 Table1.Edit;
73 theBlobStream := TBlobStream.Create(Table1B32_1, bmReadWrite);
74 try
75 thisFile := TFileStream.Create(LbxFileSelect.Filename, fmOpenRead);
76 try
77 theBlobStream.CopyFrom(thisFile, thisFile.Size);
78 finally
79 thisFile.Free;
80 end;
81 finally
82 theBlobStream.Free;
83 end;
84 Table1.Post;
85 Table1.Next;
86 end;
87 end;
88 Table1.First;
89 finally
90 LbxFileSelect.ItemIndex := curNdx;
91 LbxFileSelect.Items.EndUpdate;
92 end;
93 end;
94
95 procedure TFrmFileToFromDB.BtnFromDBClick(Sender: TObject);
96 var
97 hdr: array[1..3] of byte;
98 thisFile: TMemoryStream;
99 thisText: TMemoryStream;
100 theBlobStream: TBlobStream;
101 begin
102 thisFile := TMemoryStream.Create;
103 Memo1.Clear;
104 try
105 theBlobStream := TBlobStream.Create(TBlobField(Table1.FieldByName('B32_1')),
106 bmRead);
107 try
108 thisFile.CopyFrom(theBlobStream, theBlobStream.Size);
109 thisFile.Seek(0, soFromBeginning);
110 finally
111 theBlobStream.Free;
112 end;
113 thisFile.read(hdr[1], 3);
114 thisFile.Seek(0, soFromBeginning);
115 if (hdr[1] = $FF) and (hdr[2] = $0A) and (hdr[3] = $0) then
116 begin
117 thisText := TMemoryStream.Create;
118 try
119 try
120 ObjectResourceToText(thisFile, thisText); {DFM to text.}
121 thisText.Seek(0, soFromBeginning); {Text stream to beginning}
122 Memo1.Lines.LoadFromStream(thisText); {Text to memo1}
123 except
124 Memo1.Lines.Add('Invalid DFM image');
125 end;
126 finally
127 thisText.Free;
128 end
129 end
130 else
131 begin
132 Memo1.Lines.Add('Invalid DFM image');
133 end;
134 finally
135 thisFile.Free;
136 end;
137 end;
138
139 procedure TFrmFileToFromDB.LbxFileSelectChange(Sender: TObject);
140 begin
141 BtnToDB.Enabled := LbxFileSelect.SelCount > 0;
142 end;
143
144 procedure TFrmFileToFromDB.DataSource1DataChange(Sender: TObject; Field: TField);
145 begin
146 BtnFromDB.Click;
147 end;
148
149 end.
Solve 2:
If you develop a database related software, then very popular task is to save some
files (documents/images/reports/etc) in some BLOB field of table and use these
saved data later.
In this tip I want to show how this task could be solved.
To save a file to BLOB:
150
151 blob := yourDataset.CreateBlobStream(yourDataset.FieldByName('YOUR_BLOB'),
152 bmWrite);
153 try
154 blob.Seek(0, soFromBeginning);
155
156 fs := TFileStream.Create('c:\your_name.doc', fmOpenRead or
157 fmShareDenyWrite);
158 try
159 blob.CopyFrom(fs, fs.Size)
160 finally
161 fs.Free
162 end;
163 finally
164 blob.Free
165 end;
166
167 //to load from BLOB:
168
169 blob := yourDataset.CreateBlobStream(yourDataset.FieldByName('YOUR_BLOB'),
170 bmRead);
171 try
172 blob.Seek(0, soFromBeginning);
173
174 with TFileStream.Create('c:\your_name.doc', fmCreate) do
175 try
176 CopyFrom(blob, blob.Size)
177 finally
178 Free
179 end;
180 finally
181 blob.Free
182 end;
Using this code you can work with any database engine (BDE/ADO/DAO/ODBC/etc) and any file format (document of MS Word, spreadsheet of MS Excel, bitmap or jpeg pictures, wav-files etc)
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