delphi - 在delphi中存储之前检查图像大小

Question

如何在将图像存储到数据库之前检查图像大小。我需要在用户上传图像之前检查图像大小，以避免无法写入数据库的错误。

下面是我当前如何在数据库中插入图像的片段，它工作正常，除了大于我存储在数据库中的字段大小的图像。

数据库中的图像字段为LONGVARBINARY 484物理长度

              dtm.cds.Insert;
              Image1.Picture.LoadFromFile(OpenPictureDialog1.FileName);
              Image1.Visible := false;
              Field := TBlobField(dtm.cds.FieldByName('PICTURE'));
              Stream := dtm.cds.CreateBlobStream(field, bmwrite);

              JpegImage := TJPEGImage.Create;
              try
                     JpegImage.Assign(Image1.Picture);
                     JpegImage.SaveToStream(Stream);
              finally
                     Stream.Free;
                     dtm.cds.Post;
                     dtm.cds.ApplyUpdates(-1);
              end;

Answer 1

TField 有一个 Size属性:

Indicates the size used in the definition of the physical database field for data types that support different sizes.

尝试更多类似这样的事情:

MemStream := TMemoryStream.Create;
try
  JpegImage := TJPEGImage.Create;
  try
    Picture := TPicture.Create;
    try
      Picture.LoadFromFile(OpenPictureDialog1.FileName);
      JpegImage.Assign(Picture.Graphic);
    finally
      Picture.Free;
    end;
    JpegImage.SaveToStream(MemStream);
  finally
    JpegImage.Free;
  end;
  Field := dtm.cds.FieldByName('PICTURE');
  if MemStream.Size > Field.Size then
    raise Exception.Create('Image as a JPEG is too large to store!');
  dtm.cds.Insert;
  try
    Stream := dtm.cds.CreateBlobStream(Field, bmWrite);
    try
      Stream.CopyFrom(MemStream, 0);
    finally
      Stream.Free;
    end;
    dtm.cds.Post;
  except
    dtm.cds.Cancel;
    raise;
  end;
finally
  MemStream.Free;
end;
dtm.cds.ApplyUpdates(-1);