Deep Object Comparison Delphi

BIZ TMS Aurelius
1
Wagner

I would like your opinion on the best way to buy if two objects are equal,
being equal do not send a put to the server and inform the user that the object has not been changed;

Problem 1:

I tried to use the class TDataSnapJsonSerializer (Aurelius.Json.DataSnap), but I did not succeed
for more complex entities (with associations), since fields are returned out of order at each serialization.

Ex.:

  loEntidadeComplexa1 := FClient.Get<TEntidadeComplexa>(10);
  loJson1 := loEntidadeComplexa1.ToJsonString;  
  
  loEntidadeComplexa2 := FClient.Get<TEntidadeComplexa>(10);
  loJson2 := loEntidadeComplexa2.ToJsonString;
  
  if loJson1 <> loJson2 then
    FClient.Put(loEntidadeComplexa2)
  else
    Showmessage('No data was changed');

...

Serialization result loJson1:
{
  "$type": "App.Modelo.Entidade.TEntidadeComplexa",
  "$id": 1,
  "FNome": "FAZENDA TR\u00CAS PONTAS ALTERADO",
  "FAreaCultura": 38000,
  "FQuantidadeNascente": 3,
  "FCooperado": {
    "$proxy": "single",
    "key": null,
    "class": "",
    "member": ""
  },
  "FCulturas": {
    "$proxy": "list",
    "key": null,
    "class": "",
    "member": ""
  }, ...

Serialization result loJson2:
{
  "$type": "App.Modelo.Entidade.TEntidadeComplexa",
  "$id": 1,
  "FValidade": "2020-02-10",
  "FObservacao": null,
  "FImagemMapa": {
    "$lazyblob": true,
    "key": null,
    "class": "",
    "member": ""
  },
  "FCooperado": {
    "$proxy": "single",
    "key": null,
    "class": "",
    "member": ""
  }, ...  

Problem 2:

Accessing a property that references another entity also changes the final json.

  [Entity]
  [Table('MUNICIPIO')]
  [Sequence('SEQ_MUNICIPIO')]
  [Id('FID', TIdGenerator.IdentityOrSequence)]
  TMunicipio = class
  strict private
    [Column('ID')]
    FID: Integer;

    [Column('NOME', [TColumnProp.Unique, TColumnProp.Required], 40)]
    FNome: string;
    
    [Association([TAssociationProp.Lazy], CascadeTypeAllButRemove)]
    [ForeignKey('FK_MUNICIPIO_UF')]
    [JoinColumn('ID_UNIDADE_FEDERATIVA', [TColumnProp.Required])]
    FUnidadeFederativa: Proxy<TUnidadeFederativa>;
  protected ...
  
  loMunicipio1 := FClient.Get<TMunicipio>(12);
  loJson1 := loMunicipio1.ToJsonString;
  
  loMunicipio2 := FClient.Get<TMunicipio>(12);
  UF := loMunicipio2.UnidadeFederativa.Nome;
  loJson2 := loMunicipio2.ToJsonString;  

...
  
Serialization result loJson1:
{
  "$type": "App.Modelo.Entidade.TMunicipio",
  "$id": 1,
  "FID": 12,
  "FNome": "TR\u00CAS PONTAS",
  "FUnidadeFederativa": {
    "$proxy": "single",
    "key": null,
    "class": "",
    "member": ""
  }
}  

Serialization result loJson2:
{
  "$type": "App.Modelo.Entidade.TMunicipio",
  "$id": 1,
  "FID": 12,
  "FNome": "TR\u00CAS PONTAS",
  "FUnidadeFederativa": {
    "$type": "App.Modelo.Entidade.TUnidadeFederativa",
    "$id": 2,
    "FID": 11,
    "FNome": "MINAS GERAIS",
    "FSigla": "MG",
    "FCodigoIBGE": 31,
    "FPais": {
      "$type": "App.Modelo.Entidade.TPais",
      "$id": 3,
      "FID": 27,
      "FCodigo": 55,
      "FNomePtBr": "BRASIL",
      "FNomeEn": "BRAZIL",
      "FSigla2": "BR",
      "FSigla3": "BRA"
    }
  }
}

I think using Json is not the best option, you agree?

What is the best way to do this comparison? Does Aurelius have any features that make this easy?

Thank you


2

Hi,


You can use some methods in TMappingExplorer, for example ObjectChanged, UpdateChangedColumns or GetColumnValues. Those are methods that could help you out with that.

But, as a piece of advice, why are you doing that at client side? Shouldn't you be treating that at server-side. And in any case, when using Merge as PutMode (the default), XData will internally perform a Merge operation using Aurelius object manager at server-side, and will only update the modified columns anyway.
3
But, as a piece of advice, why are you doing that at client side?

Yes, I'm doing this from the client side, through json comparison,
because I would like to avoid bandwidth consumption and send a message to the user.

Shouldn't you be treating that at server-side...

What is the best way to treat this server side and send a message to the user that the object has not changed data.

I tested the "ObjectChanged" method of class "TMappingExplorer" but did not work as expected.

for example:

  loMunicipio1 := FClient.Get<TMunicipio>(12);  
  
  loMunicipio2 := FClient.Get<TMunicipio>(12);

  // here -> Object not changed
  if TMappingExplorer.Default.ObjectChanged(loMunicipio1,loMunicipio2) then
    ShowMessage('Object changed')
  else
    ShowMessage('Object not changed');   

  // here accesses an association
  loJson2 := loMunicipio2.UnidadeFederativa.Nome;      


  // here -> Object changed
  if TMappingExplorer.Default.ObjectChanged(loMunicipio1,loMunicipio2) then
    ShowMessage('Object changed')
  else
    ShowMessage('Object not changed'); 

Why are they different?
4

Invert the order, use ObjectChanged(loMunicipio2, loMunicipio1)

5
Ok, it worked now (Invert the order). Thanks....

What is the best way to treat this server side and send a message to the user that the object has not changed data?
6

You can use XData server-side events (OnEntityModifying for example): http://www.tmssoftware.biz/business/xdata/doc/web/onentitymodifying_event.html

7

Is what I imagined. 


But how to get the original entity? Will I have to retrieve it again through a get, and then compare them to the "ObjectChanged" method of class "TMappingExplorer"?
8
If you take a look at the method TObjectManager.InternalFlush, you will see this code:



  Old := FObjects.GetOldState(Entity);
  if Old <> nil then
  begin
    ChangedColumns := TList<string>.Create;
    try
      Explorer.UpdateChangedColumns(Entity, Old.Values, ChangedColumns);
      if ChangedColumns.Count > 0 then
        PerformUpdate(Entity, ChangedColumns);
    finally
      ChangedColumns.Free;
    end;
  end else
    PerformUpdate(Entity, nil);

You can use a similar approach. The only trick is that FObjects is private. You can try to use a hack to access a protected property:


type THackManager = class(TObjectManager);
{...}
Old := THackManager(TXDataOperationContext.Current.GetManager).ObjectMap.GetOldState(Entity);
9
Wagner

I tried to use your approach, but I'm getting error "Exception class EListError with message 'Item not found'", in the line below:

Old: = THackManager (TXDataOperationContext.Current.GetManager) .ObjectMap.GetOldState (Args.Entity);

The "FMap" field of the "TObjectMap" object does not contain any reference to the entity being changed.
10

Are you trying that in your real application or a test application? If you have a test application that can be compiled and run by us, could you send it to us via e-mail so we can implement the solution there directly and send back to you?

11

In an actual application, but I can prepare a test application.Could send it to which email?

12

support @ tmssoftware.com

13

Thank you. Indeed it was an issue with OnEntityModifying event in a very specific situation (on merging objects). We have fixed this and sent you a patch through e-mail. The fix will be included in the next XData version release.

14

Thanks,Wagner