closes #576, closes #578

library/src/main/java/org/mustangproject/Item.java

@@ -69,6 +69,9 @@ public class Item implements IZUGFeRDExportableItem {
 			icnm.getAsNodeMap("ClassifiedTaxCategory").flatMap(m -> m.getAsBigDecimal("Percent"))
 				.ifPresent(product::setVATPercent);
 		});
+		itemMap.getAsNodeMap("AssociatedDocumentLineDocument").ifPresent(icnm -> {
+			icnm.getAsString("LineID").ifPresent(this::setId);
+		});
 
 		itemMap.getAsNodeMap("Price").ifPresent(icnm -> {
 			// ubl

library/src/main/java/org/mustangproject/ZUGFeRD/IZUGFeRDExportableItem.java

@@ -153,4 +153,12 @@ public interface IZUGFeRDExportableItem extends IAbsoluteValueProvider{
 		return null;
 	}
 
+
+	/***
+	 *
+	 * @return the line ID
+	 */
+	default String getId()  {
+		return null;
+	}
 }

library/src/main/java/org/mustangproject/ZUGFeRD/ZUGFeRD2PullProvider.java

@@ -401,6 +401,10 @@ public class ZUGFeRD2PullProvider implements IXMLProvider {
 		int lineID = 0;
 		for (final IZUGFeRDExportableItem currentItem : trans.getZFItems()) {
 			lineID++;
+			String lineIDStr = Integer.toString(lineID);
+			if (currentItem.getId()!=null) {
+				lineIDStr=currentItem.getId();
+			}
 			if (currentItem.getProduct().getTaxExemptionReason() != null) {
 				exemptionReason = "<ram:ExemptionReason>" + XMLTools.encodeXML(currentItem.getProduct().getTaxExemptionReason()) + "</ram:ExemptionReason>";
 			}
@@ -408,7 +412,7 @@ public class ZUGFeRD2PullProvider implements IXMLProvider {
 			if ((getProfile() != Profiles.getByName("Minimum")) && (getProfile() != Profiles.getByName("BasicWL"))) {
 				xml += "<ram:IncludedSupplyChainTradeLineItem>" +
 					"<ram:AssociatedDocumentLineDocument>"
-					+ "<ram:LineID>" + lineID + "</ram:LineID>"
+					+ "<ram:LineID>" + lineIDStr + "</ram:LineID>"
 					+ buildItemNotes(currentItem)
 					+ "</ram:AssociatedDocumentLineDocument>"