Get Default and Custom Dimension in AX (D365O)

To Get Default Dimension

static void ShyamDEV_Dimension(Args _args)
{
    SalesTable salesTable;
    CustTable    custTable = CustTable::find("1101");
    DimensionAttributeValueSetStorage dimStorage;
    Counter i;
    DefaultDimensionView defaultDimensionView;
  DimensionAttribute dimensionAttribute;
    DimensionAttribute      dimAttribute;

 select firstOnly defaultDimensionView  join salesTable
            where defaultDimensionView.DefaultDimension == salesTable.DefaultDimension && salesTable.SalesId==whsWorkTable.OrderNum
             join dimensionAttribute where defaultDimensionView.Name == dimensionAttribute.Name
            && defaultDimensionView.Name =="BusinessUnit" ; // Port in UAT
         
  info(strFmt("%1 = %2",defaultDimensionView.Name,defaultDimensionView.DisplayValue));
info(strFmt("%1",defaultDimensionView.dimensionDiscription()));

}

To Get Custom Dimension

/// <summary>
/// Find description for custom financial dimension value
/// </summary>
/// <param name="_dimensionValue" />
/// Financial dimension value
/// </param>
/// <param name="_dimensionAttributeName" />
/// Dimension attribute name
/// </param>
/// <returns>
/// DimensionValue description
/// </returns>
/// <remarks>
/// Only for custom financial dimensions
/// </remarks>
public static Description findDimensionValueDescription(DimensionValue _dimensionValue, Name _dimensionAttributeName)
{
         DimensionFinancialTag dimensionFinancialTag;
         DimensionAttributeDirCategory dimensionAttributeDirCategory;
         DimensionAttribute dimensionAttribute;

         select firstOnly Description from dimensionFinancialTag
         where dimensionFinancialTag.Value == _dimensionValue
         join DirCategory from dimensionAttributeDirCategory
         where dimensionAttributeDirCategory.DirCategory == dimensionFinancialTag.FinancialTagCategory
         join RecId from dimensionAttribute
         where dimensionAttribute.RecId == dimensionAttributeDirCategory.DimensionAttribute
         DimensionAttribute.Name == _dimensionAttributeName;

         return dimensionFinancialTag.Description;
}

Reference