Improving the compare_entities functions

Summary

I reviewed the compare_entities function from apiutils and identified some problematic cases (e.g. multi-properties). Corresponding unit tests have been created and the functionality repaired.

This is a preparation for a comprehensive review of the merge_entities function. I think it's a good idea to merge this in a first step as it's probably independent from the review of the merge function.

Focus

This one can probably be reviewed line-by-line. Maybe look for missing test-corner-cases that might be needed. The code for checking the value for equality is still not ideal, but I think a more comprehensive review (also adding the recursive reference checker) should be postponed.

Test Environment

There are unit tests.

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• Reference related issues
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• Appropriate user and developer documentation (or not necessary)
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  • Intent of new code
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Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
• Appropriate user and developer documentation (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there specifications? Are they satisfied?

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src/caosdb/apiutils.py

@@ -267,7 +267,7 @@ def compare_entities(old_entity: Entity, new_entity: Entity,
             continue
 
         if ((old_entity_attr_exists != new_entity_attr_exists)
-            or (oldattr != newattr)):
+                or (oldattr != newattr)):
 
             if old_entity_attr_exists:
                 olddiff[attr] = oldattr
@@ -278,8 +278,16 @@ def compare_entities(old_entity: Entity, new_entity: Entity,
     # properties
 
     for prop in old_entity.properties:
+        # Find the corresponding property in new_entity:
         matching = [p for p in new_entity.properties if p.name == prop.name]
 
+        # This is needed for checking for multi properties in old_entity:
+        # TODO: is there a better way?
+        matching_old = [p for p in old_entity.properties if p.name == prop.name]
+        if len(matching_old) != 1:
+            raise NotImplementedError(
+                "Comparison not implemented for multi-properties.")
+
         if len(matching) == 0:
             olddiff["properties"][prop.name] = {}
         elif len(matching) == 1: