Add UniqueIndex for materialized views

`unique=True` on a model field in a materialized view will
generate a `ALTER TABLE` operation. This will not work,
but `CREATE UNIQUE INDEX` will.

Author: Photonios

docs/source/indexes.rst

@@ -3,6 +3,31 @@
 Indexes
 =======
 
+.. _unique_index_page:
+
+Unique Index
+-----------------------------
+The :class:`~psqlextra.indexes.UniqueIndex` lets you create a unique index. Normally Django only allows you to create unique indexes by specifying ``unique=True`` on the model field.
+
+Although it can be used on any Django model, it is most useful on views and materialized views where ``unique=True`` does not work.
+
+.. code-block:: python
+
+   from django.db import models
+   from psqlextra.indexes import UniqueIndex
+
+   class Model(models.Model):
+       class Meta:
+           indexes = [
+               UniqueIndex(fields=['name']),
+           ]
+
+       name = models.CharField(max_length=255)
+
+   Model.objects.create(name='henk')
+   Model.objects.create(name='Henk') # raises IntegrityError
+
+
 .. _conditional_unique_index_page:
 
 Conditional Unique Index

psqlextra/indexes/__init__.py

@@ -1,4 +1,9 @@
 from .case_insensitive_unique_index import CaseInsensitiveUniqueIndex
 from .conditional_unique_index import ConditionalUniqueIndex
+from .unique_index import UniqueIndex
 
-__all__ = ["ConditionalUniqueIndex", "CaseInsensitiveUniqueIndex"]
+__all__ = [
+    "UniqueIndex",
+    "ConditionalUniqueIndex",
+    "CaseInsensitiveUniqueIndex",
+]

psqlextra/indexes/unique_index.py

@@ -0,0 +1,18 @@
+import django
+
+from django.db.models.indexes import Index
+
+
+class UniqueIndex(Index):
+    def create_sql(self, *args, **kwargs):
+        if django.VERSION >= (2, 0):
+            statement = super().create_sql(*args, **kwargs)
+            statement.template = self._rewrite_sql(statement.template)
+            return statement
+
+        sql = super().create_sql(*args, **kwargs)
+        return self._rewrite_sql(sql)
+
+    @staticmethod
+    def _rewrite_sql(sql: str) -> str:
+        return sql.replace("CREATE INDEX", "CREATE UNIQUE INDEX")

tests/test_unique_index.py

@@ -0,0 +1,33 @@
+from django.db import models
+from django.db.migrations import AddIndex, CreateModel
+
+from psqlextra.indexes import UniqueIndex
+
+from .migrations import apply_migration, filtered_schema_editor
+
+
+def test_unique_index_migrations():
+    index = UniqueIndex(fields=["name", "other_name"], name="index1")
+
+    ops = [
+        CreateModel(
+            name="mymodel",
+            fields=[
+                ("name", models.TextField()),
+                ("other_name", models.TextField()),
+            ],
+            options={
+                # "indexes": [index],
+            },
+        ),
+        AddIndex(model_name="mymodel", index=index),
+    ]
+
+    with filtered_schema_editor("CREATE UNIQUE INDEX") as calls:
+        apply_migration(ops)
+
+    calls = [call[0] for _, call, _ in calls["CREATE UNIQUE INDEX"]]
+
+    db_table = "tests_mymodel"
+    query = 'CREATE UNIQUE INDEX "index1" ON "{0}" ("name", "other_name")'
+    assert str(calls[0]) == query.format(db_table)