UserConnection in D365fo

Its used when we need to commit our transaction wehen standared code doesn't Commit.
example :SalesQuotationEditLinesForm_Sales_Send > checkSales() , COC and try to write 
custom insert or update operation here while validation is failed our transactions doesn't commit

static void KlForRecordInserted(Args _args)
{
    UserConnection userConnection;
    CustTable custTable;
    ;
   
    ttsbegin;
   
    userConnection = new userConnection();
   
    custTable.clear();
    custTable.initValue();
    custTable.AccountNum = "000020";
    custTable.Name = "My Test Customer";
    custTable.setConnection(userConnection); // set userconnection
    custTable.insert();
   
    throw error("An error that causes a rollback");
    ttscommit;
}

Register override lookup in D365fo from form datasource

/// <summary>
/// Extension of the form 'SalesTable' data source 'SalesLine'.
/// </summary>
[ExtensionOf(formDataSourceStr(SalesTable, SalesLine))]
final class Sales_SalesTableForm_SalesLineDS_Extension
{
    /// <summary>
    /// COC construct to handle standard datasource init method
    /// </summary>
    /// <remarks>
    /// Method overriden to add custom logic
    /// </remarks>
    void init()
    {
        next init();

        this.m_Init();
    }

    /// <summary>
    /// COC Implementation for additional logic on init method
    /// </summary>
    void m_Init()
    {
        this.sm_ReasonCodeLookupRegisterOverride();
    }

    /// <summary>
    /// SM reason code lookup override method
    /// </summary>
    public void m_ReasonCodeLookupRegisterOverride()
    {
        FormDataSource salesLineDataSource = element.dataSource(formDataSourceStr(SalesTable, SalesLine)) as FormDataSource;
        SM_Sales_SalesTableFormRegisterMethods formRegisterMethods = new SM_Sales_SalesTableFormRegisterMethods();

        salesLineDataSource.object(fieldNum(SalesLine, SM_ReasonCode)).registerOverrideMethod(methodStr(FormDataObject, lookup),
                                methodStr(M_Sales_SalesTableFormRegisterMethods, lookupReasoncode ),
                                formRegisterMethods);
              
    }

}

/// <summary>
/// Form 'SalesTable', data source 'SalesLine' register override method implementation
/// </summary>
class Sales_SalesTableFormRegisterMethods
{
    /// <summary>
    /// Overrides <c>SM_Reasoncode</c> field lookup
    /// </summary>
    /// <param name = "_formStringControl">The control that is bound to the <c>SM_Reasoncode</c> field.</param>
    public void lookupReasoncode(FormStringControl _formStringControl)
    {
        FormRun formRun = _formStringControl.formRun();

        SalesTable salesTableLoc = formRun.dataSource(formDataSourceStr(SalesTable, SalesTable)).cursor() as SalesTable;

        SalesLine::m_lookupReasoncode(_formStringControl, salesTableLoc.DlvReason);
    }

}

/// <summary>
    /// Overrides <c>SM_Reasoncode</c> field lookup
    /// </summary>
    /// <param name = "_formStringControl">The control that is bound to the <c>SM_Reasoncode</c> field.</param>
    public static void lookupReasoncode(FormStringControl _formStringControl, DlvReasonId _dlvReason)
    {
        Query query = new Query();

        QueryBuildDataSource queryBuildDataSource = query.addDataSource(tableNum(ReasonTable));
        queryBuildDataSource.addSelectionField(fieldnum(ReasonTable, Reason));

        if (SM_CustParameters::find().ActivateReasonCode)
        {
            container conReasoncode;
            ReasonTable reasonTable;
            SM_DeliveryReasonReasonCodeCombination deliveryReasonReasonCodeCombination;

            while select ReasonCode from deliveryReasonReasonCodeCombination
                exists join reasonTable
                where reasonTable.Reason == deliveryReasonReasonCodeCombination.ReasonCode
                && deliveryReasonReasonCodeCombination.DlvReasonId == _dlvReason
                && reasonTable.SM_ActivateReasonCode == NoYes::Yes
            {
                conReasoncode += deliveryReasonReasonCodeCombination.ReasonCode;
            }

            str reasoncodes = conReasoncode != conNull() ? con2Str(conReasoncode) : SysQuery::valueEmptyString();

            queryBuildDataSource.addRange(fieldnum(ReasonTable, Reason)).value(reasoncodes);
        }
       
        SysTableLookup lookup = SysTableLookup::newParameters(tablenum(ReasonTable), _formStringControl);

        lookup.addLookupfield(fieldnum(ReasonTable, Reason));
        lookup.addLookupfield(fieldnum(ReasonTable, Description));

        lookup.parmQuery(query);
        lookup.performFormLookup();
    }

Access public variables in extension class using chain of command

When you wrap a method, you can also access public and protected methods
and variables of the base class.
CustInvoiceJour is a base class variable hence you will be able to access it. Eg.

[ExtensionOf(classStr(SalesConfirmJournalCreate))]
Final class SalesConfirmJournalCreate_Extension
{
protected void createJournalHeader()
{
next createJournalHeader();
//It's as simple as this:
custConfirmJour.SalesBalance = 0;
}
if gets an error, It's an old bug with variable names. Declare new one and use it:
protected void createJournalHeader()
{
next createJournalHeader();
CustConfirmJour custConfirmJourLocal =
custConfirmJour;
custConfirmJourLocal.MyField = 'blah-blah';
}
}

Add new fields in sysoperation dialog and get the values in controller class in AX

UIBuilder class

[ExtensionOf(classstr(ExchangeRateImportUIBuilder))]
final class PDPExchangeRateImportUIBuilder_Extension
{
    public FormBuildIntControl      intCtrl;
    public FormBuildCheckBoxControl booleanCtrl;

    public void build()
    {
        next build();

        DialogField                 dialogField;
        DialogField                 dialogFieldNoYesId;
        ExchangeRateImportRequest   dataContract1;
        FormBuildCheckBoxControl    exchangeRateFromPreviousDayControl;

        dataContract1    = this.dataContractObject();

       //  creating this field if standared code skips it to avoid type cast error in contoller at runtime
        if(exchangeRateFromPreviousDayControl == null)
        {
            dialogField = dialog.addField(extendedtypestr(ExchangeRateFromPreviousDay));
            exchangeRateFromPreviousDayControl = dialogField.control();
            exchangeRateFromPreviousDayControl.value(dataContract1.parmExchangeRateFromPreviousDay());
            exchangeRateFromPreviousDayControl.allowEdit(false);
            exchangeRateFromPreviousDayControl.visible(false);
        }

        dialogField     = dialog.addField(extendedtypestr(NumberOf),"integer","integer");
        intCtrl         = dialogField.control();
        intCtrl.value(dataContract1.parmInteg());

        dialogField     = dialog.addField(extendedtypestr(NoYesId),"boolean","boolean");
        booleanCtrl     = dialogField.control();
        booleanCtrl.value(dataContract1.parmNoYesId());
    }

}

Contract class

[ExtensionOf(ClassStr(ExchangeRateImportRequest))]
[DataContractAttribute]
final class PDPExchangeRateImportRequest_Extension
{
    public int     integ;
    public NoYesId noYesValue;

    /// <summary>
    /// data memeber attribute of Integ field
    /// </summary>
    /// <param name = "_integ">integ</param>
    /// <returns>int</returns>
    [DataMemberAttribute]
    public int parmInteg(int _integ = 0)
    {
        if (!_integ)
        {
            integ = _integ;
        }

        return integ;
    }

    /// <summary>
    /// NoyesId field
    /// </summary>
    /// <param name = "_noYesValue">NoYesValue</param>
    /// <returns>boolean</returns>
    [DataMemberAttribute]
    public NoYesId parmNoYesId(NoYesId _noYesValue = NoYes::No)
    {
        if (!_noYesValue)
        {
            noYesValue = _noYesValue;
        }

        return _noYesValue;
    }

}

Controller class

[ExtensionOf(ClassStr(ExchangeRateImportController))]
final class PDPExchangeRateImportController_Extension
{
    public const str numberof = 'Fld11_1';
    public const str noYesValue = 'Fld12_1';


    public void getFromDialog()
    {
        next getFromDialog();

        FormRun                             theDialogForm;
        ExchangeRateImportRequest           exchangeRateImportRequest;
        ExchangeRateProviderFactory         factory;

        FormIntControl intCtrl;
        FormCheckBoxControl booleanCtrl;
        FormCheckBoxControl exchangeRateFromPreviousDayControl;
       
        exchangeRateImportRequest = this.getDataContractObject(classStr(ExchangeRateImportRequest));
        theDialogForm = this.dialog().formRun();

        intCtrl = theDialogForm.control(theDialogForm.controlId(numberof));

        booleanCtrl = theDialogForm.control(theDialogForm.controlId(noYesValue));

        exchangeRateImportRequest.parmInteg(intCtrl.value());

        exchangeRateImportRequest.parmExchangeRateTypeRecId(booleanCtrl.value());

        Info(strFmt("%1--%2",intCtrl.value(), booleanCtrl.value()));

    }

}