如何从kinvey.com获取“ _id”字段值

Question

I been using kinvey.com, and every time I try to get Manga._id it returns null. Can you help me figure out why?

TManga = class
  strict private
    FSite,
    FManga,
    FID: String;
  published
    property Site        : string  read FSite        write FSite;
    property Manga       : string  read FManga       write FManga;
    property _id         : string  read FID          write FID;

///////////////////////////////////////////////////////////////////////////

var
  Mangas: TBackendObjectList<TManga>;
  Manga : TManga;
  QueryStr: TArray<string>;
  i: Integer;
begin
with xQuery do
  begin
    Execute;
    Mangas := TBackendObjectList<TManga>.Create;

    QueryStr := TArray<string>.Create('');

    xStorage.Storage.QueryObjects<TManga>('xxxx' ,QueryStr ,Mangas);

    with xListBox do
    begin
      Items.BeginUpdate;
      try
        Items.Clear;
        for I := 0 to Mangas.Count -1 do
        begin
          Manga := Mangas.Items[I];
          items.add(Manga.Site + ' - ' + Manga._id) // Manga._id this is everytime null 

        end;

      finally
        Items.EndUpdate;
      end;

    end;
  end;

http://i.hizliresim.com/M94QPN.png

Answer 1

您是否尝试在QueryStr的数组元素之一中使用值“ fields = _id”？

Answer 2

Your column _id is always null because the Kinvey API doesn't get the _id column as a simple column but as the object ID of the record. In order to get the object ID of your Manga record, you must to add a variable like this:

  oEntity: TBackendEntityValue;

So right under this line in the "for" statement:

  Manga := Mangas.Items[I];

You may add these two new lines:

oEntity := FBackendList.EntityValues[Manga]; // Gets the Kinvey object
Manga._id := oEntity.ObjectID; // Sets the _id property of the current TManga instance

One important thing you may take in mind is when you will add new records in your Kinvey collection. You don't have to write in the _id property of your new TManga item before you create your new record. However you will need to get it from Kinvey right after you insert the new record. This code was adapted from the Embarcadero's ToDo sample:

procedure TDataModule1.AddBackendItem(const AItem: TManga);
var
  oEntity: TBackendEntityValue;
begin

  // After the execution of this command the new record will be inserted in Kinvey, and the variable oEntity will get the respective object ID 
  BackendStorage1.Storage.CreateObject<TManga>(
    TMangaNames.BackendClassname, AItem, oEntity);

  AItem._id := oEntity.ObjectID; // Updates the property _id of the current instance of TManga

  FBackendList.Add(AItem, oEntity);

end;

I hope it can help you!