[英]Why is SQL Alchemy ORM's Many to Many JOIN this inefficient for me?
我在我的一个类中运行以下查询,该类采用 ORM 类,以便它可以与几个类似的表一起使用。
(
self.db.query(self.orm_contact_class)
.options(
load_only(
self.orm_contact_class.id,
self.orm_contact_class.name,
self.orm_contact_class.email_attempts_dict,
),
joinedload(
self.orm_contact_class.__dict__[self.access_from_contact_to_company]
).load_only(self.orm_company_class.domain)
)
.where(
self.orm_contact_class.email == None,
self.orm_contact_class.name != None,
self.orm_company_class.domain != None,
catch_all_conditions
)
)
这导致了这个可怕的查询:
SELECT test.crunchbase_people.id AS test_crunchbase_people_id,
test.crunchbase_people.name AS test_crunchbase_people_name,
test.crunchbase_people.email_attempts_dict AS test_crunchbase_people_email_attempts_dict,
crunchbase_companies_1.id AS crunchbase_companies_1_id,
crunchbase_companies_1.domain AS crunchbase_companies_1_domain
FROM test.crunchbase_companies,
test.crunchbase_people
LEFT OUTER JOIN (
test.crunchbase_people_crunchbase_companies AS crunchbase_people_crunchbase_companies_1
JOIN test.crunchbase_companies AS crunchbase_companies_1
ON crunchbase_companies_1.id = crunchbase_people_crunchbase_companies_1.crunchbase_companies_id)
ON test.crunchbase_people.id = crunchbase_people_crunchbase_companies_1.crunchbase_people_id
WHERE test.crunchbase_people.email IS NULL AND test.crunchbase_people.name IS NOT NULL AND test.crunchbase_companies.domain IS NOT NULL AND (test.crunchbase_companies.is_domain_catch_all = false OR test.crunchbase_companies.is_domain_catch_all IS NULL)
最终永远不会完成,如果我在 Postgres 控制台中运行它,它只会一遍又一遍地返回完全相同的行的副本!
所以它永远不会映射对象,因为查询只需要很长时间。 在没有 ORM 的情况下,有一种简单的方法可以做到这一点,并且查询在 0.5 秒内运行(并且没有像上面那样的重复项),但是我的对象没有被映射,这将导致我重构我的很多代码。
有谁知道这样的查询可能有什么问题?
正如原始帖子的评论员所建议的那样,我错过了一个显式连接,因为joinedload 不会取代它,而只是告诉哪些字段应该被预加载。
(
self.db.query(self.orm_contact_class)
.join(self.orm_contact_class.__dict__[self.access_from_contact_to_company]) # added this line
.options(
load_only(
self.orm_contact_class.id,
self.orm_contact_class.name,
self.orm_contact_class.email_attempts_dict,
),
joinedload(
self.orm_contact_class.__dict__[self.access_from_contact_to_company]
).load_only(self.orm_company_class.domain)
)
.where(
self.orm_contact_class.email == None,
self.orm_contact_class.name != None,
self.orm_company_class.domain != None,
catch_all_conditions
)
)
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