Nested json object deserializing using Delphi 2012

Question

I'm working on a wrapper for dropbox in delphi 2012. The problem I'm running into is deserializing the json responses. When I make the request for a list of folders and files in my account I get a response that looks something like this:

{
    "hash": "some_hash",
    "thumb_exists": false, 
    "bytes": 0,
    "path": "/", 
    "is_dir": true, 
    "size": "0 bytes", 
    "root": "dropbox", 
    "contents": 
    [
        {
            "revision": 11, 
            "rev": "b074cbcbb", 
            "thumb_exists": false, 
            "bytes": 0, 
            "modified": "Mon, 23 Apr 2012 19:19:27 +0000", 
            "path": "/Apps", 
            "is_dir": true, 
            "icon": "folder", 
            "root": "dropbox", 
            "size": "0 bytes"
        }, 
        {    
            "revision": 142, 
            "rev": "8e074cbcbb", 
            "thumb_exists": false, 
            "bytes": 0, 
            "modified": "Wed, 09 May 2012 22:55:44 +0000", 
            "path": "/code", 
            "is_dir": true, 
            "icon": "folder", 
            "root": "dropbox", 
            "size": "0 bytes"
        },
        {
            "revision": 7,
            "rev": "7074cbcbb", 
            "thumb_exists": false, 
            "bytes": 246000, 
            "modified": "Mon, 23 Apr 2012 18:40:51 +0000", 
            "client_mtime": "Mon, 23 Apr 2012 18:40:52 +0000", 
            "path": "/Getting Started.pdf", 
            "is_dir": false, 
            "icon": "page_white_acrobat", 
            "root": "dropbox", 
            "mime_type": "application/pdf", 
            "size": "240.2 KB"
        }
    ],
    "icon": "folder"
}

I would like to be able to parse that using a TJSONUnMarshal object, but it turns out that TJSONUnMarshal expects the json to look like this instead:

{
"type":"DropboxApiU.TFile",
"id":1,
"fields":
{
    "hash": "some_hash",
    "thumb_exists": false, 
    "bytes": 0,
    "path": "/", 
    "is_dir": true, 
    "size": "0 bytes", 
    "root": "dropbox", 
    "contents": 
    [
        {
            "type":"DropboxApiU.TFile",
            "id":1,
            "fields":
            {
                "revision": 11, 
                "rev": "b074cbcbb", 
                "thumb_exists": false, 
                "bytes": 0, 
                "modified": "Mon, 23 Apr 2012 19:19:27 +0000", 
                "path": "/Apps", 
                "is_dir": true, 
                "icon": "folder", 
                "root": "dropbox", 
                "size": "0 bytes"
            }
        },

I've looked at this page and thought it might be what I'm looking for, but it never really goes into how to use a TTypeObjectReverter (which I think is what I need to use) and I can't seem to find an example online.

What would be the best way to make this happen? I'm hoping I can just write a TTypeObjectReverter, or something similar, but I would need to see a sample to be able to wrap my head around that.

edit Here's a screenshot of the differences between the two. The red is not sent in the response from the dropbox server, but is expected by the unmarshaler.

Differences

There is missing the end of a second file. Anyway except the JSON files would be nice to include also a screenshot from some differencing tool (it's friday and I'm so lazy to do it by myself :-) — TLama
– TLama, Commented May 11, 2012 at 22:06
@TLama I uploaded a screen shot, and the second one is missing the end because all the differences are shown in the first part and I was too lazy on this glorious friday to rebuild the entire request the way delphi was expecting it :) — nick
– nick, Commented May 11, 2012 at 22:15

Linas · Accepted Answer · 2012-05-12 12:05:21Z

You could use my SvSerializer class for this task. First, you'll need to define your class which you want to serialize/deserialize, e.g.:

TDropbox = class
  private
    FHash: string;
    Fthumb_exists: Boolean;
    Fbytes: Integer;
    Fpath: string;
    Fis_dir: Boolean;
    FSize: string;
    Froot: string;
    Fcontents: TArray<TContent>;
    Ficon: string;
  public
    [SvSerialize]
    property Hash: string read FHash write FHash;
    [SvSerialize]
    property thumb_exists: Boolean read Fthumb_exists write Fthumb_exists;
    [SvSerialize]
    property bytes: Integer read Fbytes write Fbytes;
    [SvSerialize]
    property path: string read Fpath write Fpath;
    [SvSerialize]
    property is_dir: Boolean read Fis_dir write Fis_dir;
    [SvSerialize]
    property size: string read FSize write FSize;
    [SvSerialize]
    property root: string read Froot write Froot;
    [SvSerialize]
    property contents: TArray<TContent> read Fcontents write Fcontents;
    [SvSerialize]
    property icon: string read Ficon write Ficon;
  end;

TContent = record
  private
    frevision: Integer;
    Frev: string;
    Fthumb_exists: Boolean;
    Fbytes: Integer;
    fmodified: string;
    fclient_mtime: string;
    fpath: string;
    fis_dir: Boolean;
    ficon: string;
    froot: string;
    fmime_type: string;
    fsize: string;
  public
    property revision: Integer read frevision write frevision;
    property rev: string read Frev write Frev;
    property thumb_exists: Boolean read Fthumb_exists write Fthumb_exists;
    property bytes: Integer read Fbytes write Fbytes;
    property modified: string read fmodified write fmodified;
    property client_mtime: string read fclient_mtime write fclient_mtime;
    property path: string read fpath write fpath;
    property is_dir: Boolean read fis_dir write fis_dir;
    property icon: string read ficon write ficon;
    property root: string read froot write froot;
    property mime_type: string read fmime_type write fmime_type;
    property size: string read fsize write fsize;
  end;

Then add TDropbox object's instance to serializer:

FSerializer := TSvSerializer.Create();
FDropboxFile := TDropbox.Create;
FSerializer.AddObject('', FDropboxFile);

And now you can serialize/deserialize this object through SvSerializer:

FSerializer.DeSerialize(mmo1.Lines.Text{your json string, stream or filename}, TEncoding.UTF8{if it is string you must specify the encoding});
//After this line your FDropBoxFile's properties are filled from your json string

New to Delphi, your class definition's use of property construct helped me solve a deserialization issue I was battling for quite sometime!

Luis Carrasco · Accepted Answer · 2012-05-12 00:08:31Z

2

May be you could try using Progdigy´s JSON Wrapper instead?

answered May 12, 2012 at 0:08

Luis Carrasco

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