Fix #140 – indicator constraints not being removed (#144)

* fix: fixes #140 (indicator constraints not being removed)

I am not sure this is a good solution. Also, need to extend solution in
case we're adding support quadratic constraints.

* refactor: better error handling

optlang/cplex_interface.py

@@ -234,7 +234,13 @@ def get_linear_coefficients(self, variables):
     def _get_expression(self):
         if self.problem is not None:
             cplex_problem = self.problem.problem
-            cplex_row = cplex_problem.linear_constraints.get_rows(self.name)
+            try:
+                cplex_row = cplex_problem.linear_constraints.get_rows(self.name)
+            except CplexSolverError as e:
+                if 'CPLEX Error  1219:' not in str(e):
+                    raise e
+                else:
+                    cplex_row = cplex_problem.indicator_constraints.get_linear_components(self.name)
             variables = self.problem._variables
             expression = add(
                 [mul((symbolics.Real(cplex_row.val[i]), variables[ind])) for i, ind in
@@ -640,7 +646,7 @@ def __init__(self, problem=None, *args, **kwargs):
                 )
             try:
                 objective_name = self.problem.objective.get_name()
-            except cplex.exceptions.CplexSolverError as e:
+            except CplexSolverError as e:
                 if 'CPLEX Error  1219:' not in str(e):
                     raise e
             else:
@@ -885,7 +891,9 @@ def _add_constraints(self, constraints, sloppy=False):
     def _remove_constraints(self, constraints):
         super(Model, self)._remove_constraints(constraints)
         for constraint in constraints:
-            if constraint.is_Linear:
+            if constraint.indicator_variable is not None:
+                self.problem.indicator_constraints.delete(constraint.name)
+            elif constraint.is_Linear:
                 self.problem.linear_constraints.delete(constraint.name)
             elif constraint.is_Quadratic:
                 self.problem.quadratic_constraints.delete(constraint.name)

optlang/interface.py

@@ -1511,8 +1511,6 @@ def _add_constraints(self, constraints, sloppy=False):
             constraint._problem = self
 
     def _remove_constraints(self, constraints):
-        for constraint in constraints:  # TODO: remove this hack that fixes problems with lazy solver expressions.
-            constraint.expression
         keys = [constraint.name for constraint in constraints]
         if len(constraints) > 350:  # Need to figure out a good threshold here
             self._constraints = self._constraints.fromkeys(set(self._constraints.keys()).difference(set(keys)))

optlang/tests/abstract_test_cases.py

@@ -182,6 +182,12 @@ def test_indicator_constraint_support(self):
             model = self.interface.Model()
             model.add(constraint)
             model.update()
+            self.assertEqual(constraint.problem, model)
+            self.assertIn(constraint, model.constraints)
+            model.remove(constraint.name)
+            model.update()
+            self.assertEqual(constraint.problem, None)
+            self.assertNotIn(constraint, model.constraints)
         else:
             self.assertRaises(
                 optlang.exceptions.IndicatorConstraintsNotSupported,