Add support for creating materialized view without data

Fixes #216

Author: Photonios

psqlextra/backend/migrations/operations/create_materialized_view_model.py

@@ -23,10 +23,13 @@ def __init__(
         view_options={},
         bases=None,
         managers=None,
+        *,
+        with_data: bool = True,
     ):
         super().__init__(name, fields, options, bases, managers)
 
         self.view_options = view_options or {}
+        self.with_data = with_data
 
     def state_forwards(self, app_label, state):
         state.add_model(
@@ -46,7 +49,9 @@ def database_forwards(self, app_label, schema_editor, from_state, to_state):
 
         model = to_state.apps.get_model(app_label, self.name)
         if self.allow_migrate_model(schema_editor.connection.alias, model):
-            schema_editor.create_materialized_view_model(model)
+            schema_editor.create_materialized_view_model(
+                model, with_data=self.with_data
+            )
 
     def database_backwards(
         self, app_label, schema_editor, from_state, to_state
@@ -63,6 +68,9 @@ def deconstruct(self):
         if self.view_options:
             kwargs["view_options"] = self.view_options
 
+        if self.with_data is not False:
+            kwargs["with_data"] = self.with_data
+
         return name, args, kwargs
 
     def describe(self):

psqlextra/backend/schema.py

@@ -61,9 +61,12 @@ class PostgresSchemaEditor(SchemaEditor):
     sql_create_view = "CREATE VIEW %s AS (%s)"
     sql_replace_view = "CREATE OR REPLACE VIEW %s AS (%s)"
     sql_drop_view = "DROP VIEW IF EXISTS %s"
-    sql_create_materialized_view = (
+    sql_create_materialized_view_with_data = (
         "CREATE MATERIALIZED VIEW %s AS (%s) WITH DATA"
     )
+    sql_create_materialized_view_without_data = (
+        "CREATE MATERIALIZED VIEW %s AS (%s) WITH NO DATA"
+    )
     sql_drop_materialized_view = "DROP MATERIALIZED VIEW %s"
     sql_refresh_materialized_view = "REFRESH MATERIALIZED VIEW %s"
     sql_refresh_materialized_view_concurrently = (
@@ -548,10 +551,19 @@ def delete_view_model(self, model: Type[Model]) -> None:
         sql = self.sql_drop_view % self.quote_name(model._meta.db_table)
         self.execute(sql)
 
-    def create_materialized_view_model(self, model: Type[Model]) -> None:
+    def create_materialized_view_model(
+        self, model: Type[Model], *, with_data: bool = True
+    ) -> None:
         """Creates a new materialized view model."""
 
-        self._create_view_model(self.sql_create_materialized_view, model)
+        if with_data:
+            self._create_view_model(
+                self.sql_create_materialized_view_with_data, model
+            )
+        else:
+            self._create_view_model(
+                self.sql_create_materialized_view_without_data, model
+            )
 
     def replace_materialized_view_model(self, model: Type[Model]) -> None:
         """Replaces a materialized view with a newer version.

tests/test_schema_editor_view.py

@@ -1,6 +1,9 @@
-from django.db import connection, models
+import pytest
+
+from django.db import OperationalError, connection, models
 
 from psqlextra.backend.schema import PostgresSchemaEditor
+from psqlextra.error import extract_postgres_error_code
 
 from . import db_introspection
 from .fake_model import (
@@ -103,6 +106,34 @@ def test_schema_editor_create_delete_materialized_view():
     assert model._meta.db_table not in db_introspection.table_names(True)
 
 
+@pytest.mark.django_db(transaction=True)
+def test_schema_editor_create_materialized_view_without_data():
+    underlying_model = get_fake_model({"name": models.TextField()})
+
+    model = define_fake_materialized_view_model(
+        {"name": models.TextField()},
+        {"query": underlying_model.objects.filter(name="test1")},
+    )
+
+    underlying_model.objects.create(name="test1")
+    underlying_model.objects.create(name="test2")
+
+    schema_editor = PostgresSchemaEditor(connection)
+    schema_editor.create_materialized_view_model(model, with_data=False)
+
+    with pytest.raises(OperationalError) as exc_info:
+        list(model.objects.all())
+
+    pg_error = extract_postgres_error_code(exc_info.value)
+    assert pg_error == "55000"  # OBJECT_NOT_IN_PREREQUISITE_STATE
+
+    model.refresh()
+
+    objs = list(model.objects.all())
+    assert len(objs) == 1
+    assert objs[0].name == "test1"
+
+
 def test_schema_editor_replace_materialized_view():
     """Tests whether creating a materialized view and then replacing it with
     another one (thus changing the backing query) works as expected."""