Revert change to persistent_base and instead declare xpres.var as not…

… hashable

pyomo/common/collections/component_map.py

@@ -47,6 +47,15 @@ def _unhashable(val):
     def _tuple(self, val):
         return tuple(self[i.__class__](i) for i in val)
 
+    def hashable(self, obj, hashable=None):
+        if isinstance(obj, type):
+            cls = obj
+        else:
+            cls = type(cls)
+        if hashable is None:
+            return self.get(cls, None) is self._hashable
+        self[cls] = self._hashable if hashable else self._unhashable
+
 
 _hasher = _Hasher()
 
@@ -78,6 +87,8 @@ class ComponentMap(AutoSlots.Mixin, collections.abc.MutableMapping):
 
     __slots__ = ("_dict",)
     __autoslot_mappers__ = {'_dict': _rehash_keys}
+    # A "public" interface to the global _hasher dict
+    hasher = _hasher
 
     def __init__(self, *args, **kwds):
         # maps id_hash(obj) -> (obj,val)

pyomo/solvers/plugins/solvers/persistent_solver.py

@@ -400,15 +400,11 @@ def remove_var(self, var):
                 + 'objective or one or more constraints'
             )
         solver_var = self._pyomo_var_to_solver_var_map[var]
+        self._remove_var(solver_var)
         self._symbol_map.removeSymbol(var)
         del self._referenced_variables[var]
         del self._pyomo_var_to_solver_var_map[var]
         del self._solver_var_to_pyomo_var_map[solver_var]
-        # Note: we want to remove the solver_var from all our internal
-        # mappings *before* removing it from the solver (the solver may
-        # invalidate the object, leading to exceptions when looking it
-        # up in ComponentMaps)
-        self._remove_var(solver_var)
 
     """ This method should be implemented by subclasses."""
 

pyomo/solvers/plugins/solvers/xpress_direct.py

@@ -162,6 +162,13 @@ def _addConstraint(
         XpressDirect._getDuals = lambda self, prob, con: prob.getDuals(con)
         XpressDirect._getRedCosts = lambda self, prob, con: prob.getRedCosts(con)
 
+        # Note that as of 9.5, xpress.var raises an exception when
+        # compared using '==' after it has been removed from the model.
+        # This can fould up ComponentMaps in the persistent interface,
+        # so we will hard-code the `var` as not being hashable (so the
+        # ComponentMap will use the id() as the key)
+        ComponentMap.hasher.hashable(xpress.var, False)
+
 
 class _xpress_importer_class(object):
     # We want to be able to *update* the message that the deferred