Problem bei JSON-Abfrage

[Uwe Raabe]

Ich baue mir da immer anhand der API passende Objektstrukturen zusammen. Dann wird der Abruf nicht nur wesentlich simpler, man bekommt auch gleich die Typsicherheit dazu. Ich habe hier nur einen Teil der Felder deklariert. Alle übrigen werden ignoriert. Das lässt sich relativ leicht erweitern.

Delphi-Quellcode:

uses
  System.JSON, REST.Json;

type
  TArtist = class
  private
    FName: string;
  public
    property Name: string read FName;
  end;

  TAlbum = class
  private
    FArtists: TArray<TArtist>;
    FName: string;
  public
    property Artists: TArray<TArtist> read FArtists;
    property Name: string read FName;
  end;

  TTrack = class
  private
    FAlbum: TAlbum;
    FArtists: TArray<TArtist>;
    FId: string;
    FName: string;
  public
    property Album: TAlbum read FAlbum;
    property Artists: TArray<TArtist> read FArtists;
    property Id: string read FId;
    property Name: string read FName;
  end;

  TUser = class
  private
    FDisplay_name: string;
  public
    property Display_name: string read FDisplay_name;
  end;

  TPlaylistTrack = class
  private
    FAdded_at: TDateTime;
    FAdded_by: TUser;
    FIs_local: Boolean;
    FTrack: TTrack;
  public
    property Added_at: TDateTime read FAdded_at;
    property Added_by: TUser read FAdded_by;
    property Is_local: Boolean read FIs_local;
    property Track: TTrack read FTrack;
  end;

  TPaging<T: class> = class
  private
    FHref: string;
    FItems: TArray<T>;
    FLimit: Integer;
    FNext: string;
    FOffset: Integer;
    FPrevious: string;
    FTotal: Integer;
  public
    property Href: string read FHref;
    property Items: TArray<T> read FItems;
    property Limit: Integer read FLimit;
    property Next: string read FNext;
    property Offset: Integer read FOffset;
    property Previous: string read FPrevious;
    property Total: Integer read FTotal;
  end;

  TPlayList = class
  private
    FName: string;
    FTracks: TPaging<TPlaylistTrack>;
  public
    property Name: string read FName;
    property Tracks: TPaging<TPlaylistTrack> read FTracks;
  end;

Der eigentliche Abrufcode beschränkt auf die im Eingangspost gezeigten Daten sieht dann so aus:

Delphi-Quellcode:

function TSpManager.GetPlaylistTracks(PlaylistID: string; List: TStrings): string; // Liste der Track-IDs aus Playlist holen
var
  playlist: TPlaylist;
  track: TPlaylistTrack;
begin
  result := '';
  RESTRequest1.Resource := 'v1/playlists/{PlaylistID}'; // Accesspoint der Spotify Web-API
  RESTRequest1.AddParameter('PlaylistID', PlaylistID);
  RESTRequest1.Execute;
  if RestResponse1.JSONValue is TJSONObject then begin
    playlist := TJson.JsonToObject<TPlaylist>(TJSONObject(RESTResponse1.JSONValue));
    if playlist <> nil then begin
      Result := playlist.Name;
      if playlist.Tracks <> nil then begin
        for track in playlist.Tracks.Items do begin
          if track.Track <> nil then begin
            List.Add(track.Track.Id);
          end;
        end;
      end;
    end;
  end;
end;