Support ForeignKey.to_field

Fix #7

Signed-off-by: Byron Ruth <b@devel.io>

modeltree/tree.py

@@ -132,14 +132,6 @@ def m2m_reverse_field(self):
         else:
             return f.field.m2m_reverse_name()
 
-    @property
-    def foreignkey_field_column(self):
-        f = getattr(self.parent_model, self.accessor_name)
-        if self.reverse:
-            return f.related.field.column
-        else:
-            return f.field.column
-
     @property
     def foreignkey_field(self):
         f = getattr(self.parent_model, self.accessor_name)
@@ -183,7 +175,8 @@ def get_joins(self, **kwargs):
             self.get_connection(None, self.parent.db_table, None, None)
         joins.append(copy)
 
-        # Setup two connections for m2m.
+        # Setup two connections for m2m. The first is the left model table
+        # to the "intermediate table" to the right model table.
         if self.relation == 'manytomany':
             c1 = self.get_connection(
                 self.parent.db_table,
@@ -216,13 +209,20 @@ def get_joins(self, **kwargs):
             joins.append(copy1)
             joins.append(copy2)
         else:
+            # A reverse direction goes from referred model back to model
+            # that is referring to it.
+            if self.reverse:
+                lhs = self.foreignkey_field.rel.get_related_field().column
+                rhs = self.foreignkey_field.column
+            else:
+                lhs = self.foreignkey_field.column
+                rhs = self.foreignkey_field.rel.get_related_field().column
+
             c1 = self.get_connection(
                 self.parent.db_table,
                 self.db_table,
-                self.parent.pk_column if self.reverse
-                else self.foreignkey_field_column,
-                self.foreignkey_field_column if self.reverse
-                else self.pk_column,
+                lhs,
+                rhs,
             )
 
             copy = kwargs.copy()

tests/cases/regressions/issue7/models.py

@@ -0,0 +1,38 @@
+from django.db import models
+
+
+class A(models.Model):
+    study_id = models.CharField(max_length=20,
+                                unique=True,
+                                db_column='study_id')
+
+    class Meta:
+        db_table = 'a'
+
+
+class B(models.Model):
+    study_id = models.ForeignKey('A',
+                                 to_field='study_id',
+                                 unique=True,
+                                 db_column='study_id')
+
+    class Meta:
+        db_table = 'b'
+
+
+class C(models.Model):
+    id = models.IntegerField(primary_key=True, db_column='c_id')
+    bs = models.ManyToManyField('B', through='CB')
+
+    class Meta:
+        db_table = 'c'
+
+
+class CB(models.Model):
+    c = models.ForeignKey('C', db_column='some_c_id')
+    sid = models.ForeignKey('B',
+                            to_field='study_id',
+                            db_column='study_id')
+
+    class Meta:
+        db_table = 'cb'

tests/cases/regressions/issue7/tests.py

@@ -0,0 +1,39 @@
+from django.test import TestCase
+from modeltree.tree import trees
+from .models import A, B, C
+
+
+class Test(TestCase):
+    """Wrong foreign key used when constructing joins.
+    https://github.com/cbmi/modeltree/issues/7
+    """
+    def test_fk(self):
+        mt = trees.create(A)
+
+        joins = mt.get_joins(B)
+        lhs, rhs = joins[1]['connection'][2][0]
+        self.assertEqual((lhs, rhs), ('study_id', 'study_id'))
+
+        mt = trees.create(B)
+        joins = mt.get_joins(A)
+        lhs, rhs = joins[1]['connection'][2][0]
+        self.assertEqual((lhs, rhs), ('study_id', 'study_id'))
+
+    def test_m2m(self):
+        mt = trees.create(B)
+
+        joins = mt.get_joins(C)
+        lhs, rhs = joins[1]['connection'][2][0]
+        self.assertEqual((lhs, rhs), ('id', 'study_id'))
+
+        lhs, rhs = joins[2]['connection'][2][0]
+        self.assertEqual((lhs, rhs), ('some_c_id', 'c_id'))
+
+        mt = trees.create(C)
+
+        joins = mt.get_joins(B)
+        lhs, rhs = joins[1]['connection'][2][0]
+        self.assertEqual((lhs, rhs), ('c_id', 'some_c_id'))
+
+        lhs, rhs = joins[2]['connection'][2][0]
+        self.assertEqual((lhs, rhs), ('study_id', 'id'))