F fix merge entity conflicts

Summary

Part of https://gitlab.indiscale.com/caosdb/customers/leibniz-zmt/management/-/issues/125. Adds a new apiutils.empty_diff function to check for the identity of two Entity objects in the sense of no differences between the two entities. It also adds optional arguments to compare_entities and merge_entities to determine whether or not referenced Entity objects will be compared/merged.

Focus

Mainly, new cases to the value comparison of reference properties have been added to the compare_entities function. Note that the compare_referenced_records argument of the compare_entities function defaults False in order to restore the previous behavior. In contrast, the default of merge_references_with_empty_diffs of merge_entities is True because a) the function is Experimental anyway, so breaking previous behavior is ok, and b) in most of the (e.g., crawler) cases this is probably what a merge is expected to do.

Test Environment

Unit tests should be sufficient; but you can also test it with ZMT's Pangaea crawler.

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CHANGELOG.md

@@ -9,8 +9,23 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added ###
 
+* `apiutils.empty_diff` function that returns `True` if the diffs of two
+  entities found with the `compare_entitis` function are empty, `False`
+  otherwise.
+
 ### Changed ###
 
+* `apiutils.compare_entities` now has an optional `compare_referenced_records`
+  argument to compare referenced Entities recursively (fomerly, only the
+  referenced Python objects would be compared). The default is `False` to
+  recover the original behavior.
+* `apiutils.merge_entities` now has an optional
+  `merge_references_with_empty_diffs` argument that determines whether a merge
+  of two entities will be performed if they reference identical records (w.r.t
+  th above `empty_diff` function). Formerly this would have caused a merge
+  conflict if the referenced record(s) were identical, but stored in different
+  Python objects.
+
 ### Deprecated ###
 
 ### Removed ###