Question

我有SqlAlchemy数据模型（错过了其他字段）：

session.query(District)\
    .options(joinedload(District.region))\
    .order_by(Region.name, Region.id)\
    .slice(0, 25)

并构建此查询：

ProgrammingError: (ProgrammingError) invalid reference to FROM-clause entry for table "region"

查询发出错误ORDER BY。调查后发现原始SQL错误的原因。 SELECT district.id AS district_id, district.name AS district_name, district.region_id AS district_region_id, region_1.id AS region_1_id FROM district LEFT OUTER JOIN region AS region_1 ON region_1.id = district.region_id ORDER BY region.name, region.id LIMIT 25子句不正确：

ORDER BY

进入region子句使用region_1而不是正确的别名<tags-input ng-model="recps" display-property="recipient" replace-spaces-with-dashes="false" on-tag-removing="removeRecipient($tag)" allowed-tags-pattern="^[A-Za-z0-9]+([-_.][A-Za-z0-9]+)*@[A-Za-z0-9]+([-_.][A-Za-z0-9]+)*.[A-Za-z]{2,5}$" on-invalid-tag="invalidTagInput($tag)" ng-focus="validData.validRecipients=true;"> </tags-input> <div class="email-address box" ng-show="!validData.validRecipients"> {{validationMsg}} </div> //js code here $scope.invalidTagInput = function(tag) { $scope.validData.validRecipients = false; };，这会引发错误。

在这种情况下如何构建正确的查询？

Answer 1

查看sqlalchemy文档The Zen of Eager Loading

他们准确描述了您的问题，解决方案将是：

In [10]:
    
q = session.query(District)\
    .join(District.region)\
    .options(joinedload(District.region))\
    .order_by(Region.name, Region.id)\
    .slice(0, 25)

print(q)

SELECT district.id AS district_id, district.region_id AS district_region_id, district.name AS district_name, region_1.id AS region_1_id, region_1.name AS region_1_name 
FROM district JOIN region ON region.id = district.region_id LEFT OUTER JOIN region AS region_1 ON region_1.id = district.region_id ORDER BY region.name, region.id
 LIMIT ? OFFSET ?

（我必须将名字添加到您发布的课程中。）

相关引用：

我们在上面看到的是我们使用Query.join（）来提供JOIN 我们想在后续查询标准中使用的条款，而我们的条款 joinload（）的用法只关心它的加载 User.addresses集合，用于结果中的每个用户。在这种情况下，这两个连接最可能看起来多余 - 它们是。

（在您的情况下，将User.addresses替换为District.region。

如果您按照链接进行操作，可以在一个联接中再次进行此操作：

In [15]:

from sqlalchemy.orm import aliased, outerjoin, contains_eager

ralias = aliased(Region)

q2 = session.query(District).\
    outerjoin(ralias, District.region).\
    options(contains_eager(District.region, alias=ralias)). \
    order_by(Region.name, Region.id).\
    slice(0, 25)

print(q2)

SELECT region_1.id AS region_1_id, region_1.name AS region_1_name, district.id AS district_id, district.region_id AS district_region_id, district.name AS district_name 
FROM district LEFT OUTER JOIN region AS region_1 ON region_1.id = district.region_id ORDER BY region.name, region.id
 LIMIT ? OFFSET ?

希望它有所帮助。

应用order_by时对表的引用无效

1 个答案: