ENH: new function to merge entities

src/caosdb/apiutils.py

@@ -712,10 +712,52 @@ def copy_entity(entity: Entity):
     return new
 
 
+def merge_entities(entity_a: Entity, entity_b: Entity):
+    """
+    Create a new entity which is a copy of entity_a and merge it with entity_b such that
+    it compare_entities would report zero differences.
+    """
+    new = copy_entity(entity_a)
+
+    # Compare both entities:
+    diff_r1, diff_r2 = compare_entities(entity_a, entity_b)
+
+    # Go through the comparison and try to apply changes to entity_a:
+    for key in diff_r2["parents"]:
+        new.add_parent(entity_b.get_parent(key))
+
+    for key in diff_r2["properties"]:
+        if key in diff_r1["properties"]:
+            if (diff_r1["properties"][key]["importance"] !=
+                diff_r2["properties"][key]["importance"]):
+                raise NotImplementedError()
+            
+            for attribute in ("datatype", "unit", "value"):
+                if diff_r1["properties"][key][attribute] is None:
+                    setattr(new.get_property(key), attribute,
+                            diff_r2["properties"][key][attribute])
+                else:
+                    raise RuntimeError("Merge conflict.")
+        else:
+            new.add_property(
+                entity_b.get_property(key),
+                importance=entity_b.get_importance(key))
+
+    for special_attribute in ("name", "description"):
+        sa_new = getattr(new, special_attribute)
+        sa_b = getattr(entity_b, special_attribute)
+        if sa_new != sa_b:
+            if sa_new is None:
+                setattr(new, special_attribute, sa_b)
+            else:
+                raise RuntimeError("Merge conflict.")
+    return new
+
+
 def describe_diff(olddiff, newdiff, name=None, as_update=True):
     description = ""
 
-    for attr in list(set(list(olddiff.keys())+list(newdiff.keys()))):
+    for attr in list(set(list(olddiff.keys()) + list(newdiff.keys()))):
         if attr == "parents" or attr == "properties":
             continue
         description += "{} differs:\n".format(attr)