add functionality to deal with an empty RHS #259

- Relevant when a filter input has a boolean operator but there's only one condition in that list. Makes the boolean operator redundant but is still an edge case we should support
- Additional test cases have been added to cover this

datagateway_api/src/search_api/nested_where_filters.py

@@ -20,13 +20,28 @@ def __init__(self, lhs, rhs, joining_operator):
 
         self.lhs = lhs
         self.rhs = rhs
+        self.joining_operator = f" {joining_operator} "
 
     def __str__(self):
         """
         Join the condition on the left with the one on the right with the boolean
         operator
         """
-        return f"({str(self.lhs)} {self.joining_operator} {str(self.rhs)})"
+        boolean_algebra_list = [self.lhs, self.rhs]
+        try:
+            boolean_algebra_list.remove(None)
+        except ValueError:
+            # If neither side contains `None`, we should continue as normal
+            pass
+
+        for i in range(len(boolean_algebra_list)):
+            # Convert inputs to JPQL-ready
+            boolean_algebra_list[i] = str(boolean_algebra_list[i])
+
+        # TODO - LHS and RHS need to be able to deal with a list of
+        # `SearchAPIWhereFilters`
+
+        return f"({self.joining_operator.join(boolean_algebra_list)})"
 
     def __repr__(self):
         return f"LHS: {repr(self.lhs)}, RHS: {repr(self.rhs)}, Operator: {repr(self.joining_operator)}"

test/search_api/test_nested_where_filters.py

@@ -8,6 +8,8 @@ class TestNestedWhereFilters:
     @pytest.mark.parametrize(
         "lhs, rhs, joining_operator, expected_where_clause",
         [
+            pytest.param("A", None, "AND", "(A)", id="(A) w/ misc. AND"),
+            pytest.param("A", None, "OR", "(A)", id="(A) w/ misc. OR"),
             pytest.param("A", "B", "AND", "(A AND B)", id="(A AND B)"),
             pytest.param("A", "B", "OR", "(A OR B)", id="(A OR B)"),
             pytest.param(