Get json of update

BIZ TMS XData
1

Hi,

How can I get the json when data has been updated?

Should I use event 'Module.Events.OnEntityModified.Subscribe' in XDataServer and if so how can it be called?

I am using XData only (not Aurelius).

2

The JSON value is very low level info, it can be encrypted, compressed, etc. XData deserializes and JSON on the fly, thus it doesn't cache the JSON anywhere.

In other words, it's not impossible, but not trivial at all, to get the JSON of the request. Is there anything specific you want to accomplish with that?

3

The json would be used for an audit trail (store the changed field values).

4

For such functionality I recommend using low-level Aurelius events, which will give you the changes in each table of the database:

https://doc.tmssoftware.com/biz/aurelius/guide/events.html#onupdated-event

5

Are there examples how to use these events with XDataserver?

6

Here is an example:

There is also a good implementation in the Aurelius Music Library demo.

7

I am checking out the demo.

procedure TAuditLogForm.AureliusModelEvents1Updated(Sender: TObject; Args: TUpdatedArgs);
var
Pair: TPair<string, Variant>;
OldValue: Variant;
begin
if not cbEnable.Checked then Exit;

Log(Format('Updated: %s', [EntityDesc(Args.Entity, Args.Manager)]));
for Pair in Args.NewColumnValues do
if not (Args.OldColumnValues.TryGetValue(Pair.Key, OldValue) and (OldValue = Pair.Value)) then
Log(Format(' %s Changed from "%s" to "%s"',
[Pair.Key, TUtils.VariantToString(OldValue), TUtils.VariantToString(Pair.Value)]));
BreakLine;
end;

However the following function misses the Manager object.

TServerContainer.XDataServerEntityModified(Sender: TObject; Args: TEntityModifiedArgs);

8

The demo (and my answer) mentions Aurelius server-side events.
The one you mention is XData event. It's different. I recommend using Aurelius one.

9

Hi Wagner,

I don't use (need) Aurelius.

var
ObjManager: TObjectManager;
begin
ObjManager := TXDataOperationContext.Current.GetManager;

TFile.AppendAllText('test.log',Format('Updated: %s', [ ObjManager.ToString]), TEncoding.UTF8);

Result of the last line is TEMPLOYEES(3). That is the modified record (ID=3).
Can't I access the field values from there? If so how?

10

I don't understand your question.
If you don't use Aurelius, why are you asking how to get the fields from the Aurelius manager?

11

Sorry if I am not clear.

I have a simple TXDataServer project and would like to make an audit log of changed fields.

The Server Side events described on page Server-Side Events | TMS XData documentation should be used if I understand correct.

Args.Manager is not accessible from 'Module.Events.OnEntityModified.Subscribe' so there I got an reference to TXDataOperationContext.Current.GetManager.

12

Which changed fields? Are you using automatic Aurelius CRUD endpoints, or are you implementing your own service operations using service contract interfaces.

No. If automatic Aurelius CRUD endpoints are being used - that's what most of server-side events are for - then you should use the low-level Aurelius events as I previously mentioned.

13

Automatic Aurelius CRUD endpoints are used.

I will check out the low-level Aurelius events.

14

Thanks Wagner for pointing out into the right direction.

The following code seems to work.

var
sCols : string;
sOldValue : Variant;
sNewValue : Variant;
begin

TMappingExplorer.Default.Events.OnUpdated.Subscribe(
procedure(Args: TUpdatedArgs)
begin
sCols := '';
for var sCols in Args.ChangedColumnNames do
begin

  try
    sOldValue := '';
    sNewValue := '';
    Args.OldColumnValues.TryGetValue(sCols, sOldValue);
    Args.NewColumnValues.TryGetValue(sCols, sNewValue);

    TFile.AppendAllText('test.log',Format('"{%s}" changed from {%s} to {%s}', [sCols, sOldValue, sNewValue]) + sLineBreak,TEncoding.UTF8);
  except
  end;
end;

end
);

Is it possible to get the primary key (id) of the changed record?

1 Like
15

All values are available in Args.NewColumnValues, so you can simply get the value of Id field from that.

16

Does that mean that for every entity (table) I need to provide the primary key?

If the primary key (key=fieldname, value=id) could be fetched in the event the function could be used for all entities.

17

Usually customers have the primary key field named the same for all tables and entities. For example, 'ID" or something like that.

Or, at the very least, the primary key field is named using some criteria, like table name + id.

I assume it's not your case, then? Still. you can retrieve metadata about the entities, for example, you can get the primary key field name this way:

PKFieldName := TObjectManager(Args.Manager).Explorer
  .GetEntityType(Args.Entity).Id.Columns[0].Name;

Of course, I recommend you break this into smaller pieces, check for nil, check for Columns length, etc., but you get the idea.

18

That does the trick. Thanks!

1 Like
19

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