Hi @hotdok  I Hope you wanted to load all the active vendors if I’m not wrong. If yes, you can use like below.

#region VendorID
		public abstract class vendorID : PX.Data.BQL.BqlInt.Field<vendorID> { }
		/// <summary>
		/// Identifier of the <see cref="Vendor"/>, whom the document belongs to.
		/// </summary>
		/VendorActive(
			Visibility = PXUIVisibility.SelectorVisible, 
			DescriptionField = typeof(Vendor.acctName), 
			CacheGlobal = true, 
			Filterable = true)]

		public virtual int? VendorID
		{
			get;
			set;
		}
		#endregion

Thanks for reply. But I wanted differents stuff. As I wrote I need get all vendors for exact sales order. I need PXSelector attribute for extension property declaration. This property should return list of all vendors for opened sales order.

Figured out myself. This is how it works for me

[PXSelector(typeof(Search2<Vendor.bAccountID, InnerJoin<PO.POVendorInventory,
                On<PO.POVendorInventory.vendorID, Equal<Vendor.bAccountID>>>
                    , Where<PO.POVendorInventory.inventoryID, In2<Search<SOLine.inventoryID, Where<SOLine.orderNbr, Equal<Current<SOOrder.orderNbr>>>>>>>)
 

Thank you for sharing your solution with the community @hotdok!