From 0bc971e464b57898087c4ef807bd86d43af7d75b Mon Sep 17 00:00:00 2001
From: Derek Brandao <dbrandao@google.com>
Date: Tue, 12 Mar 2019 17:51:47 +0000
Subject: [PATCH] Remove circular dependency between conditions and
 relationships

I've changed the return type of the constraints property so that
relationships no longer depend on conditions, breaking the circular
dependency.
---
 spanner_orm/condition.py    | 11 ++++++++++-
 spanner_orm/relationship.py | 32 ++++++++++++++++++++------------
 2 files changed, 30 insertions(+), 13 deletions(-)

diff --git a/spanner_orm/condition.py b/spanner_orm/condition.py
index 98b7aa2..b410420 100644
--- a/spanner_orm/condition.py
+++ b/spanner_orm/condition.py
@@ -178,10 +178,19 @@ def bind(self, model):
 
   @property
   def conditions(self):
+    """Generate the child conditions based on the relationship constraints."""
     if not self.relation:
       raise error.SpannerError(
           'Condition must be bound before conditions is called')
-    return self.relation.conditions + self._conditions
+    relation_conditions = []
+    for constraint in self.relation.constraints:
+      # This is backward from what you might imagine because the condition will
+      # be processed from the context of the destination model
+      relation_conditions.append(
+          ColumnsEqualCondition(constraint.destination_column,
+                                constraint.origin_class,
+                                constraint.origin_column))
+    return relation_conditions + self._conditions
 
   @property
   def destination(self):
diff --git a/spanner_orm/relationship.py b/spanner_orm/relationship.py
index f44d413..38a6248 100644
--- a/spanner_orm/relationship.py
+++ b/spanner_orm/relationship.py
@@ -16,13 +16,21 @@
 
 from __future__ import annotations
 
-from typing import Dict, List, Type, Union
+from typing import Any, Dict, List, Type, Union
 
-from spanner_orm import condition
+import dataclasses
 from spanner_orm import error
 from spanner_orm import model
 
 
+@dataclasses.dataclass
+class RelationshipConstraint:
+  destination_class: Type[Any]
+  destination_column: str
+  origin_class: Type[Any]
+  origin_column: str
+
+
 class Relationship(object):
   """Helps define a foreign key relationship between two models."""
 
@@ -52,8 +60,8 @@ def __init__(self,
     self.origin = None
 
   @property
-  def conditions(self) -> List[condition.Condition]:
-    assert self.origin, 'Origin must be set before conditions is called'
+  def constraints(self) -> List[RelationshipConstraint]:
+    assert self.origin, 'Origin must be set before constraints is called'
     return self._parse_constraints()
 
   @property
@@ -66,9 +74,9 @@ def destination(self) -> Type[model.Model]:
   def single(self) -> bool:
     return self._single
 
-  def _parse_constraints(self) -> List[condition.Condition]:
+  def _parse_constraints(self) -> List[RelationshipConstraint]:
     """Validates the dictionary of constraints and turns it into Conditions."""
-    conditions = []
+    constraints = []
     for origin_column, destination_column in self._constraints.items():
       if origin_column not in self.origin.schema:
         raise error.SpannerError(
@@ -77,10 +85,10 @@ def _parse_constraints(self) -> List[condition.Condition]:
       if destination_column not in self.destination.schema:
         raise error.SpannerError(
             'Destination column must be present in destination model')
-      # This is backward from what you might imagine because the condition will
-      # be processed from the context of the destination model
-      conditions.append(
-          condition.ColumnsEqualCondition(destination_column, self.origin,
-                                          origin_column))
 
-    return conditions
+      # TODO(dbrandao): remove when pytype #234 is fixed
+      constraints.append(
+          RelationshipConstraint(self.destination, destination_column,
+                                 self.origin, origin_column))  # type: ignore
+
+    return constraints