Dynamics 365 - Table Extension Predefined Method() and Userdefined Method():

public static class SalesLine_Extension
{
    [PostHandlerFor(tableStr(SalesLine), tableMethodStr(SalesLine, insert))]
    public static void SalesLine_Post_insert(XppPrePostArgs args)
    {
        SalesLine                  saleslineLoc;
        FormDataSource      salesFormDataSource;           
      
        saleslineLoc        =  args.getthis();

        if(saleslineLoc.SalesId)
        {           
            Info("SalesID existed");
         }
         salesFormDataSource =  FormDataUtil::getFormDataSource(saleslineLoc);
               
         if(salesFormDataSource)
         {
                 salesFormDataSource.research(true);
         }
     }
public static void updateDefaultWarehouse(SalesLine _salesLine)
    {
        InventTable         inventTable;
        ;       
        inventTable   = InventTable::find(_salesLine.ItemId);
    }

[DataEventHandler(tableStr(SalesLine), DataEventType::ModifiedFieldValue)]
    public static void SalesLine_onModifiedFieldValue(Common sender, DataEventArgs e)
    {
        SalesLine       salesLineLocal = sender;
        Table              table1;
       
       
        if(salesLineLocal.SalesId)
       {        
            ttsbegin;
            table1.OrderNumber       = salesLineLocal.SalesId;
            table1.SalesType         = salesLineLocal.SalesType;
            table1.ItemId            = salesLineLocal.ItemId;
            table1.insert();
            ttscommit;
        }
    }
[PostHandlerFor(tableStr(SalesLine), tableMethodStr(SalesLine, update))]
    public static void SalesLine_Post_update(XppPrePostArgs args)
    {
        SalesLine   salesLineLocal;
        SalesTable  salesTable;

        salesLineLocal        =  args.getthis();
        ttsbegin;
            salesTable = salesTable::find(salesLineLocal.SalesId, true);
            if (salesTable)
            {
                salesTable.FieldId= SalesTable_Extension::MethodName(salesTable);
                salesTable.update();
            }
            ttscommit;
        }
[PostHandlerFor(tableStr(SalesLine), tableMethodStr(SalesLine, modifiedField))]
    public static void SalesLine_Post_modifiedField(XppPrePostArgs args)
    {
        FieldId fieldId = args.getArg('_fieldId');
        SalesLine salesLine = args.getThis();

        switch (fieldId)
        {
             case fieldNum(SalesLine, NewItemNumber):
               
               if (salesLine.NewItemNumber)                    
                {
                    ItemId itemId = salesLine.ItemId;
                    Info(strfmt("%1, " ItemId"));
                }
                break;     
        }
    }
[PostHandlerFor(tableStr(SalesLine), tableMethodStr(SalesLine, delete))]
    public static void SalesLine_Post_delete(XppPrePostArgs args)
    {
        SalesLine           salesLine;
        TableName       tableName;       
        Args                _args = new Args();

        salesLine=  args.getthis();

        if(salesLine.RecId)
        {
            ttsbegin;
            delete_from tableName
                where  tableName.OrderNumber    == salesLine.SalesId
                    && tableName.ItemId         == salesLine.ItemId
                    && tableName.LineNum        == salesLine.LineNum;
            ttscommit;
        }
    }

Dynamics 365 - DataSource Method:

public class InventLocation_Extension
{
    ///

    /// Post event handler for InventLocation SalesLine Initialized event.
    ///

    ///
    ///

[FormDataSourceEventHandler(formDataSourceStr(InventLocation, InventLocation), FormDataSourceEventType::Initialized)]
    public static void InventLocation_OnInitialized(FormDataSource sender, FormDataSourceEventArgs e)
    {
        InventLocation  inventLocation = sender.cursor();
        if (inventLocation.InventLocationId)
    {
        info("There is inventLocation Id existed");
    }
    else
    {
        info("There is NO inventLocation Id");
    }
    }
}