Question

在Django中，我经常声明应该进行的查询次数，以便单元测试能够捕获新的N + 1查询问题

from django import db
from django.conf import settings
settings.DEBUG=True

class SendData(TestCase):
    def test_send(self):
        db.connection.queries = []
        event = Events.objects.all()[1:]
        s = str(event) # QuerySet is lazy, force retrieval
        self.assertEquals(len(db.connection.queries), 2)

在SQLAlchemy中，通过设置echo标志来启用对STDOUT的跟踪发动机

engine.echo=True

编写计算SQLAlchemy查询数量的测试的最佳方法是什么？

class SendData(TestCase):
    def test_send(self):
        event = session.query(Events).first()
        s = str(event)
        self.assertEquals( ... , 2)

Answer 1

使用SQLAlchemy Core Events记录/跟踪已执行的查询（您可以从单元测试中附加它，这样它们就不会影响您在实际应用程序上的性能：

event.listen(engine, "before_cursor_execute", catch_queries)

现在编写函数catch_queries，其方式取决于您的测试方式。例如，您可以在测试语句中定义此函数：

def test_something(self):
    stmts = []
    def catch_queries(conn, cursor, statement, ...):
        stmts.append(statement)
    # Now attach it as a listener and work with the collected events after running your test

上述方法只是一个灵感。对于扩展的情况，您可能希望拥有在每次测试后清空的事件的全局缓存。原因是在0.9（当前开发）之前没有用于删除事件侦听器的API。因此，创建一个访问全局列表的全局侦听器。

Answer 2

我为此目的创建了一个上下文管理器类：

class DBStatementCounter(object):
    """
    Use as a context manager to count the number of execute()'s performed
    against the given sqlalchemy connection.

    Usage:
        with DBStatementCounter(conn) as ctr:
            conn.execute("SELECT 1")
            conn.execute("SELECT 1")
        assert ctr.get_count() == 2
    """
    def __init__(self, conn):
        self.conn = conn
        self.count = 0
        # Will have to rely on this since sqlalchemy 0.8 does not support
        # removing event listeners
        self.do_count = False
        sqlalchemy.event.listen(conn, 'after_execute', self.callback)

    def __enter__(self):
        self.do_count = True
        return self

    def __exit__(self, *_):
        self.do_count = False

    def get_count(self):
        return self.count

    def callback(self, *_):
        if self.do_count:
            self.count += 1

Answer 3

使用flask_sqlalchemy.get_debug_queries() btw的方法如何。这是Flask Debug Toolbar内部检查其source

使用的方法

from flask_sqlalchemy import get_debug_queries


def test_list_with_assuring_queries_count(app, client):
    with app.app_context():
        # here generating some test data
        for _ in range(10):
            notebook = create_test_scheduled_notebook_based_on_notebook_file(
                db.session, owner='testing_user',
                schedule={"kind": SCHEDULE_FREQUENCY_DAILY}
            )
            for _ in range(100):
                create_test_scheduled_notebook_run(db.session, notebook_id=notebook.id)
    with app.app_context():
        # after resetting the context call actual view we want asserNumOfQueries
        client.get(url_for('notebooks.personal_notebooks'))
        assert len(get_debug_queries()) == 3

请记住，要重置上下文并计数，您必须在要测量的确切内容之前致电with app.app_context()。

如何在单元测试中统计sqlalchemy查询

3 个答案: