Select the entry which has smaller dictonary order when merge

CHANGELOG.md

@@ -490,6 +490,7 @@ Note that this project **does not** adhere to [Semantic Versioning](http://semve
 - We added an option in preferences to allow for integers in field "edition" when running database in bibtex mode. [#4680](https://github.com/JabRef/jabref/issues/4680)
 - We added the ability to use negation in export filter layouts. [#5138](https://github.com/JabRef/jabref/pull/5138)
 - Focus on Name Area instead of 'OK' button whenever user presses 'Add subgroup'. [#6307](https://github.com/JabRef/jabref/issues/6307)
+- We changed the behavior of merging that the entry which has "smaller" bibkey will be selected. [#7395](https://github.com/JabRef/jabref/issues/7395)
 
 ### Fixed
 

src/main/java/org/jabref/gui/mergeentries/MergeEntriesAction.java

@@ -13,9 +13,11 @@
 import org.jabref.gui.undo.NamedCompound;
 import org.jabref.gui.undo.UndoableInsertEntries;
 import org.jabref.gui.undo.UndoableRemoveEntries;
+import org.jabref.logic.bibtex.comparator.EntryComparator;
 import org.jabref.logic.l10n.Localization;
 import org.jabref.model.database.BibDatabaseContext;
 import org.jabref.model.entry.BibEntry;
+import org.jabref.model.entry.field.InternalField;
 
 public class MergeEntriesAction extends SimpleCommand {
 
@@ -52,7 +54,19 @@ public void execute() {
         BibEntry one = selectedEntries.get(0);
         BibEntry two = selectedEntries.get(1);
 
-        MergeEntriesDialog dlg = new MergeEntriesDialog(one, two);
+        // compare two entries
+        BibEntry first;
+        BibEntry second;
+        EntryComparator entryComparator = new EntryComparator(false, false, InternalField.KEY_FIELD);
+        if (entryComparator.compare(one, two) <= 0) {
+            first = one;
+            second = two;
+        } else {
+            first = two;
+            second = one;
+        }
+
+        MergeEntriesDialog dlg = new MergeEntriesDialog(first, second);
         dlg.setTitle(Localization.lang("Merge entries"));
         Optional<BibEntry> mergedEntry = dialogService.showCustomDialogAndWait(dlg);
         if (mergedEntry.isPresent()) {

src/main/java/org/jabref/logic/bibtex/comparator/EntryComparator.java

@@ -72,6 +72,9 @@ public int compare(BibEntry e1, BibEntry e2) {
             // Sort by type.
             f1 = e1.getType();
             f2 = e2.getType();
+        } else if (sortField.equals(InternalField.KEY_FIELD)) {
+            f1 = e1.getCitationKey().orElse(null);
+            f2 = e2.getCitationKey().orElse(null);
         } else if (sortField.isNumeric()) {
             try {
                 Integer i1 = Integer.parseInt((String) f1);

src/test/java/org/jabref/logic/bibtex/comparator/EntryComparatorTest.java

@@ -1,6 +1,7 @@
 package org.jabref.logic.bibtex.comparator;
 
 import org.jabref.model.entry.BibEntry;
+import org.jabref.model.entry.field.InternalField;
 import org.jabref.model.entry.field.StandardField;
 
 import org.junit.jupiter.api.Test;
@@ -69,4 +70,35 @@ void bothEntriesNumericAscending() throws Exception {
 
         assertEquals(-1, entryComparator.compare(entry1, entry2));
     }
+
+    @Test
+    void compareObjectsByKeyAscending() {
+        BibEntry e1 = new BibEntry();
+        BibEntry e2 = new BibEntry();
+        e1.setCitationKey("Mayer2019b");
+        e2.setCitationKey("Mayer2019a");
+        assertEquals(1, new EntryComparator(false, false, InternalField.KEY_FIELD).compare(e1, e2));
+        assertEquals(-1, new EntryComparator(false, false, InternalField.KEY_FIELD).compare(e2, e1));
+    }
+
+    @Test
+    void compareObjectsByKeyWithNull() {
+        BibEntry e1 = new BibEntry();
+        BibEntry e2 = new BibEntry();
+        e1.setCitationKey("Mayer2019b");
+        assertEquals(-1, new EntryComparator(false, false, InternalField.KEY_FIELD).compare(e1, e2));
+        assertEquals(1, new EntryComparator(false, false, InternalField.KEY_FIELD).compare(e2, e1));
+    }
+
+    @Test
+    void compareObjectsByKeyWithBlank() {
+        BibEntry e1 = new BibEntry();
+        BibEntry e2 = new BibEntry();
+        e1.setCitationKey("Mayer2019b");
+        e2.setCitationKey(" ");
+        assertEquals(-1, new EntryComparator(false, false, InternalField.KEY_FIELD).compare(e1, e2));
+        assertEquals(1, new EntryComparator(false, false, InternalField.KEY_FIELD).compare(e2, e1));
+    }
 }
+
+