Attempt at fixing #158 by returning raw values from the DB

`return_model=True` would break any rows with JSONField as it
would try to convert from a JSON string to a Python object. However,
the original input data was already partially converted.

By forcing the database to return the values it inserted, we
get a raw JSON string and the converted applies normally.

psqlextra/query.py

@@ -165,14 +165,14 @@ def bulk_insert(
                 deduped_rows.append(row)
 
         compiler = self._build_insert_compiler(deduped_rows, using=using)
-        objs = compiler.execute_sql(return_id=True)
+        objs = compiler.execute_sql(return_id=not return_model)
         if return_model:
             return [
                 self._create_model_instance(dict(row, **obj), compiler.using)
                 for row, obj in zip(deduped_rows, objs)
             ]
-        else:
-            return [dict(row, **obj) for row, obj in zip(deduped_rows, objs)]
+
+        return [dict(row, **obj) for row, obj in zip(deduped_rows, objs)]
 
     def insert(self, using: Optional[str] = None, **fields):
         """Creates a new record in the database.

tests/test_on_conflict.py

@@ -1,7 +1,9 @@
+import django
 import pytest
 
 from django.core.exceptions import SuspiciousOperation
 from django.db import connection, models
+from django.utils import timezone
 
 from psqlextra.fields import HStoreField
 from psqlextra.models import PostgresModel
@@ -412,3 +414,39 @@ def test_bulk_return_models(conflict_action):
     for index, obj in enumerate(objs, 1):
         assert isinstance(obj, model)
         assert obj.id == index
+
+
+@pytest.mark.skipif(
+    django.VERSION < (3, 1),
+    reason="Django < 3.1 doesn't implement JSONField",
+)
+@pytest.mark.parametrize("conflict_action", ConflictAction.all())
+def test_bulk_return_models_converters(conflict_action):
+    """Tests whether converters are properly applied when using
+    return_model=True."""
+
+    model = get_fake_model(
+        {
+            "name": models.TextField(unique=True),
+            "data": models.JSONField(unique=True),
+            "updated_at": models.DateTimeField(),
+        }
+    )
+
+    now = timezone.now()
+
+    rows = [
+        dict(name="John Smith", data={"a": 1}, updated_at=now.isoformat()),
+        dict(name="Jane Doe", data={"b": 2}, updated_at=now),
+    ]
+
+    objs = model.objects.on_conflict(["name"], conflict_action).bulk_insert(
+        rows, return_model=True
+    )
+
+    for index, (obj, row) in enumerate(zip(objs, rows), 1):
+        assert isinstance(obj, model)
+        assert obj.id == index
+        assert obj.name == row["name"]
+        assert obj.data == row["data"]
+        assert obj.updated_at == now