Hi Petar, thank you for your help. Now I am able to get child transactions. I did other testing to see what happens:

var hierarchicalGridChildren = $("#MyGrid").igHierarchicalGrid("allChildren");

var transLevel4 = hierarchicalGridChildren.igGrid("transactionsAsString");
var transLevel3 = JSON.stringify(hierarchicalGridChildren.igGrid("pendingTransactions"));
var transLevel2 = JSON.stringify(hierarchicalGridChildren.igGrid("allTransactions"));
var transLevel1 = JSON.stringify($("#MyGrid").igGrid("allTransactions"));

I modified rowId 1, added rowId 5, and deleted rowId 4. Look the result of this at the image below (debug).

As you can see transLevel4 and transLevel2 have the same result (in this case transLevel4 and transLevel3 has nothing to do with the real level in the grid, it is just a name). Now I realize why transLevel3 is empty: there are no pending transactions because I am using AutoCommit(true). transLevel1 is empty because I didn't edit any parent row. Another interesting thing is that using stringify or transactionsAsString has the same effect. (Question 1) Does transactionsAsString use stringify behind the scene?

Regarding to iggridupdatingrowadded I have an issue: setting AutoCommit(false), new child rows are lost after pressing enter on the new row.

(Question 2) How to fix that?

And one more thing. I realized that new child rows inherit the parent's Id if the parent is not new, but when you add a new parent their children don't inherit the parent's Id. (Question 3) How to get the parent's Id and set the child's foreignkey?

Please guys I need to get this fixed before next monday :( Question 3 is the most important to me. I have tried many things. This is what I have till now: 

$(document).delegate("#MyGrid", "iggridupdatinggenerateprimarykeyvalue", function (evt, ui) {
pk = pk - 1;
ui.value = pk;
});

$(document).delegate("#MyGrid", "iggridupdatingrowadded", function (evt, ui) {

// getting the parent grid row data
var parentRow = $(ui.owner.element).parents("tr[data-container='true']").prev("tr");
var parentRowId = $(parentRow).attr("data-id");
if (parentRowId == undefined) return;

var parentRowGrid = $(parentRow).closest("table");
var parentKey = $(parentRowGrid).igGrid("getCellValue", parseInt(parentRowId), "Id");

// doesn't work
//ui.values["CategoryId"] = parentKey;

// doesn't work
//var dataRecord = $("#MyGrid").igGrid("findRecordByKey", ui.rowID);
//dataRecord.CategoryId = parentKey;

// doesn't work
//var childGrids = $("#MyGrid").igHierarchicalGrid("allChildren");
//var dataRecord = $(childGrids).igGrid("findRecordByKey", ui.rowID);
//dataRecord.CategoryId = parentKey;

/* with this (last two line of code) I receive the CategoryId but when parsing it in the server there is an error:'System.Runtime.Serialization.SerializationException'
I think it is because transactions are not aggregated (because of AutoCommit(true), and because AgreggateTransactions(true) and because if I
don't use AutoCommit(true) then new children on new parents can't be added... it is a chain of issues :(

This is what the server receive:

transactionsLevel1:[{"type":"newrow","tid":"c055","row":{"Id":-1,"Name":"AAA","Description":"AAA"},"rowId":-1}]
transactionsLevel2:[{"type":"newrow","tid":"99b5","row":{"Id":-2,"Name":"BBBBB","CategoryId":null},"rowId":-2},{"type":"cell","rowId":-1,"tid":"a635","col":"CategoryId","value":-1}]

As you see there are two transactions for the rowId:-2, one when row is added and another when CategoryId is updated.
*/

var childGrids = $("#MyGrid").igHierarchicalGrid("allChildren");
$(childGrids[0]).igGridUpdating("setCellValue", ui.rowID, "CategoryId", parentKey);

});

Please Petar, do not leave me alone! Be a good guy and help me :)

Well, I found the best solution till now: make your own aggregated transaction log :) When I finish it I would like to share it here.

Hi Stamen,

I have a hierarchical grid where I am facing issue for adding rows to child grid with existing rows. I tried your js that you recommended above. Its does insert the foreign key in ui.values,but when the transactions are posted, I dont see it. The "_addrow" function in infragistics.core.js is being hit before "iggridupdatingrowadding" function. So your js is not changing the actual transaction log due to which the inserted foreign key is not posted in transactions. Please advice.

Fantastic!!! that is a good new. Thank you so much for listening to customers :)

Hello Luis,

I am glad I was able to help! We are also determined to get this implemented in the code so you don't need to have some records in the children data sources to enable foreign key resolution. I have logged this as a work item in our internal tracking system with a Development ID of 185386. A support case is created on your behalf with number CAS-146925-F2J0Z4 , so that you can be notified when it is resolved.
You can find your active cases under Account - Support Activity in our website. Select your ticket and go to Development Issues tab.

Once you get the service release containing the fix you will no longer need this workaround.

Thank you for using Infragistics forums!

Best regards,

Stamen Stoychev

THANK YOU SO MUCH! :)

It just works beautifully!!! I hope you add this functionality out of the box, this is very important when you are doing batch updating. Fortunately I am using negative numbers for primary and foreign keys for new rows in the grid, so that makes things simpler. In the server I change those negative numbers for real keys (actually the database does it). Thank you good man :)

Hello Luis,

The reason the foreign key is not automatically set for this case is that the data source of the child grid contains no records initially. Updating can only check for the foreign key within the records it sees and at the moment there is no communication built-in for the feature to ask parents for this information. We'll discuss internally whether or not such functionality should be implemented so we can cover the use-case. If such decision is made I'll create an internal work item and link it to the case created for this forums post. In this way you'll get notified once the implementation is available.

In the meantime you can use the workaround I've prepared. The idea behind it is to use the id of the child grid to extract the foreign key from it. It's not the cleanest solution but it's the shortest one by far, any other requiring traversing the hierarchical structure and identifying whose child the grid throwing the event is. The extracted key is then added to the row object "rowAdding" passes as an event argument. To keep the event binding consistent with your other code it would look something like this:

            $(document).delegate("#grid1", "iggridupdatingrowadding", function (evt, ui) {
                var id = ui.owner.grid.id(),
                    match = id.match(/_([-0-9]*)_/),
                    fk = match && match.length === 2 ? parseInt(match[1], 10) : null;
                if (fk !== null && ui.owner.grid.options.foreignKey) {
                    ui.values[ui.owner.grid.options.foreignKey] = fk;
                }
            });

Please, have in mind that the regex used may need to be modified if you are using anything other than numbers (positive or negative) as PKs. You'll have to ensure it works properly for your hierarchical grid.

I am attaching my sample for reference. I hope this helps! Please, let me know if you have any other questions and/or concerns!

Best regards,

Stamen Stoychev