django/tests/queries/test_explain.py

import json
import unittest
import xml.etree.ElementTree

from django.db import NotSupportedError, connection, transaction
from django.db.models import Count
from django.test import TestCase, skipIfDBFeature, skipUnlessDBFeature
from django.test.utils import CaptureQueriesContext

from .models import Tag


@skipUnlessDBFeature("supports_explaining_query_execution")
class ExplainTests(TestCase):
    def test_basic(self):
        querysets = [
            Tag.objects.filter(name="test"),
            Tag.objects.filter(name="test").select_related("parent"),
            Tag.objects.filter(name="test").prefetch_related("children"),
            Tag.objects.filter(name="test").annotate(Count("children")),
            Tag.objects.filter(name="test").values_list("name"),
            Tag.objects.order_by().union(Tag.objects.order_by().filter(name="test")),
            Tag.objects.all().select_for_update().filter(name="test"),
        ]
        supported_formats = connection.features.supported_explain_formats
        all_formats = (
            (None,)
            + tuple(supported_formats)
            + tuple(f.lower() for f in supported_formats)
        )
        for idx, queryset in enumerate(querysets):
            for format in all_formats:
                with self.subTest(format=format, queryset=idx):
                    with self.assertNumQueries(1), CaptureQueriesContext(
                        connection
                    ) as captured_queries:
                        result = queryset.explain(format=format)
                        self.assertTrue(
                            captured_queries[0]["sql"].startswith(
                                connection.ops.explain_prefix
                            )
                        )
                        self.assertIsInstance(result, str)
                        self.assertTrue(result)
                        if format == "xml":
                            try:
                                xml.etree.ElementTree.fromstring(result)
                            except xml.etree.ElementTree.ParseError as e:
                                self.fail(
                                    f"QuerySet.explain() result is not valid XML: {e}"
                                )
                        elif format == "json":
                            try:
                                json.loads(result)
                            except json.JSONDecodeError as e:
                                self.fail(
                                    f"QuerySet.explain() result is not valid JSON: {e}"
                                )

    @skipUnlessDBFeature("validates_explain_options")
    def test_unknown_options(self):
        with self.assertRaisesMessage(ValueError, "Unknown options: test, test2"):
            Tag.objects.all().explain(test=1, test2=1)

    def test_unknown_format(self):
        msg = "DOES NOT EXIST is not a recognized format."
        if connection.features.supported_explain_formats:
            msg += " Allowed formats: %s" % ", ".join(
                sorted(connection.features.supported_explain_formats)
            )
        with self.assertRaisesMessage(ValueError, msg):
            Tag.objects.all().explain(format="does not exist")

    @unittest.skipUnless(connection.vendor == "postgresql", "PostgreSQL specific")
    def test_postgres_options(self):
        qs = Tag.objects.filter(name="test")
        test_options = [
            {"COSTS": False, "BUFFERS": True, "ANALYZE": True},
            {"costs": False, "buffers": True, "analyze": True},
            {"verbose": True, "timing": True, "analyze": True},
            {"verbose": False, "timing": False, "analyze": True},
            {"summary": True},
        ]
        if connection.features.is_postgresql_12:
            test_options.append({"settings": True})
        if connection.features.is_postgresql_13:
            test_options.append({"analyze": True, "wal": True})
        for options in test_options:
            with self.subTest(**options), transaction.atomic():
                with CaptureQueriesContext(connection) as captured_queries:
                    qs.explain(format="text", **options)
                self.assertEqual(len(captured_queries), 1)
                for name, value in options.items():
                    option = "{} {}".format(name.upper(), "true" if value else "false")
                    self.assertIn(option, captured_queries[0]["sql"])

    @unittest.skipUnless(connection.vendor == "mysql", "MySQL specific")
    def test_mysql_text_to_traditional(self):
        # Ensure these cached properties are initialized to prevent queries for
        # the MariaDB or MySQL version during the QuerySet evaluation.
        connection.features.supported_explain_formats
        with CaptureQueriesContext(connection) as captured_queries:
            Tag.objects.filter(name="test").explain(format="text")
        self.assertEqual(len(captured_queries), 1)
        self.assertIn("FORMAT=TRADITIONAL", captured_queries[0]["sql"])

    @unittest.skipUnless(
        connection.vendor == "mysql", "MariaDB and MySQL >= 8.0.18 specific."
    )
    def test_mysql_analyze(self):
        qs = Tag.objects.filter(name="test")
        with CaptureQueriesContext(connection) as captured_queries:
            qs.explain(analyze=True)
        self.assertEqual(len(captured_queries), 1)
        prefix = "ANALYZE " if connection.mysql_is_mariadb else "EXPLAIN ANALYZE "
        self.assertTrue(captured_queries[0]["sql"].startswith(prefix))
        with CaptureQueriesContext(connection) as captured_queries:
            qs.explain(analyze=True, format="JSON")
        self.assertEqual(len(captured_queries), 1)
        if connection.mysql_is_mariadb:
            self.assertIn("FORMAT=JSON", captured_queries[0]["sql"])
        else:
            self.assertNotIn("FORMAT=JSON", captured_queries[0]["sql"])


@skipIfDBFeature("supports_explaining_query_execution")
class ExplainUnsupportedTests(TestCase):
    def test_message(self):
        msg = "This backend does not support explaining query execution."
        with self.assertRaisesMessage(NotSupportedError, msg):
            Tag.objects.filter(name="test").explain()