Asynchrone LoadData

BIZ TMS XData
1

I have an entity TPerson and a lazy association to TPersonMemos. (Master/Detail)
One Person has many memos. The loadingprocess is too slow to load the memo data immediately.


I use Omnithread Library. How can I load the memos?

Here are my code for loading the Person:


function TdmPerson.LoadPerson(APersonID: TGuid; AJobNum: Integer; ACallback: TModelCallbackEvent): Boolean;
begin
  Async(
    procedure begin
      FPerson := XClient.Get<TPerson, TGuid>(APersonID);
    end)
  .Await(
    procedure begin
      if assigned(ACallback) then
        if FPerson <> nil then
          ACallback( self, AJobNum, GUIDToString( FPerson.PersonID))
        else
          ACallback( self, AJobNum, '');
    end);
end;

And what can I do for Memos


function TdmPerson.LoadPersonMemo( APersonID: TGuid; AJobNum: Integer; ACallback: TModelCallbackEvent): Boolean;
begin
  Async(
    procedure begin
      FPerson.PersonMemoList. := XClient. ... ???
    end)
  .Await(
    procedure begin
      if assigned(ACallback) then
        // Do something
    end);
end;

2

I don't want to change the data. I will only show the memos.

3
How is your mapping? Is PersonMemoList lazy load (proxy) or not?
If it's lazy load, you can simply read the property:

function TdmPerson.LoadPersonMemo( APersonID: TGuid; AJobNum: Integer; ACallback: TModelCallbackEvent): Boolean;
begin
  Async(
    procedure begin
      FPerson.PersonMemoList:
    end)
  .Await(
    procedure begin
      if assigned(ACallback) then
        // Do something
    end);
end;
4

It works, but I get an exception at point 3

1:  FPerson.PersonMemoList;


2: function TPerson.GetPersonMemoList: TList<TPersonMemo>;
begin
  result := FPersonMemoList.Value;
end;

3: (in unit Aurelius.Types.Proxy;)
function Proxy<T>.GetValue: T;
begin
  // No need to check for FLoaded, just optimization
  if not FLoaded then Load;
  Result := FValue;
end;

Here is the mapping:



  [Entity]
  [Table('t_p_person')]
  [Id('FPersonID', TIdGenerator.None)]
  TPerson = class
  private
    [Column('p_id', [TColumnProp.Required])]
    FPersonID: TGuid;
    
--->   Here some other columns    
    
    [ManyValuedAssociation([TAssociationProp.Lazy, TAssociationProp.Required], [TCascadeType.SaveUpdate, TCascadeType.Merge, TCascadeType.Remove], 'FPersonID')]
    FPersonMemoList: Proxy<TList<TPersonMemo>>;
    
    function GetPersonMemoList: TList<TPersonMemo>;
  public
    constructor Create;
    destructor Destroy; override;
    property PersonID: TGuid read FPersonID write FPersonID;
    property PersonMemoList: TList<TPersonMemo> read GetPersonMemoList;
  end;



  [Entity]
  [Table('t_p_memo')]
  [Id('FPersonMemoID', TIdGenerator.None)]
  TPersonMemo = class
  private
    [Column('pm_id', [TColumnProp.Required])]
    FPersonMemoID: TGuid;
    
    [Column('pm_memo', [], 32000)]
    FMemo: Nullable<string>;
    
    [Association([TAssociationProp.Lazy, TAssociationProp.Required], CascadeTypeAll - [TCascadeType.Remove])]
    [JoinColumn('p_id', [TColumnProp.Required], 'p_id')]
    FPersonID: Proxy<TPerson>;
    function GetPersonID: TPerson;
    procedure SetPersonID(const Value: TPerson);
  public
    property PersonMemoID: TGuid read FPersonMemoID write FPersonMemoID;
    property Memo: Nullable<string> read FMemo write FMemo;
    property PersonID: TPerson read GetPersonID write SetPersonID;
  end;

I think, the fault is because I use a thread.

I have no inits and the only line code is to call PersonMemoList in Thread-Execute (Async-Proc)
5

How OTL works:

I call a procedure in "Async" (this is the thread) and if it ends the lines in "Await" are executed;

6

The proxy uses the same XClient object to load the proxied list. You must be sure XClient object is still "alive" (not destroyed) by the time FPerson.PersonMemoList is called.

7
Yes, the xClient is still alive.

My mistake was here:
I loaded the person and the memos almost simultaneously

Calling the LoadPersonMemo after person isLoaded and all is working fine


procedure TffKunde.Init;
begin
  inherited;
  pvm := TPersonViewmodel.Create;
  pvm.OnLoadPerson := PersonGeladen;
  pvm.LoadPerson( StringToGUID( InputValue.AsString));
  pvm.LoadPersonMemo;
end;

Thank you, for all your work, Wagner.