Improve backwards compatibility for pickled models (#1332)

* fill in _gpr if missing

* make statement more general to capture v0.22.x as well

release-notes/next-release.md

@@ -4,11 +4,13 @@
 
 ## Fixes
 
-COBRApy is now compatible with the latest numpy versions and pin to a lower version 
+COBRApy is now compatible with the latest numpy versions and pin to a lower version
 has been removed.
 
 ## Other
 
+Backwards compatibility for pickled models has been improved.
+
 ## Deprecated features
 
 ## Backwards incompatible changes

src/cobra/core/reaction.py

@@ -926,6 +926,8 @@ def __setstate__(self, state: Dict) -> None:
             state["_upper_bound"] = state.pop("upper_bound")
 
         # Used for efficient storage in newer cobrapy versions
+        if "_gpr" not in state:
+            state["_gpr"] = state["_gene_reaction_rule"]
         if type(state["_gpr"]) is str:
             state["_gpr"] = GPR.from_string(state["_gpr"])
 

tests/test_core/test_core_reaction.py

@@ -1037,3 +1037,14 @@ def test_gpr_serialization(model: Model) -> None:
     """Verify that reactions GPRs are serialized compactly as str."""
     state = model.reactions[0].__getstate__()
     assert type(state["_gpr"]) == str
+
+
+def test_gpr_serialization_backwards_compatibility(model: Model) -> None:
+    """Verify that GPR serialization is backwards compatible."""
+    state = model.reactions[0].__getstate__()
+    print(state)
+    state["gene_reaction_rule"] = state["_gpr"]  # old format
+    del state["_gpr"]
+    rxn = Reaction("test")
+    rxn.__setstate__(state)
+    assert isinstance(rxn.gpr, GPR)