Peewee 3-排序依据和递归公用表表达式（cte）

Question

工具：Peewee 3，SQLite，Python 3

Peewee 3递归公用表表达式（cte）的官方文档：http://docs.peewee-orm.com/en/latest/peewee/querying.html#common-table-expressions

我将家谱存储在称为Person的简单自引用表中。结构（如下所示）：id，name，parent，custom_order

注意：-如果此人是祖先/根项目，则parent字段等于null，否则，如果此人是孩子，则等于父记录的id-custom_order是浮点数（分数是确定用户最喜欢的人的分数）

目标：我想检索整个家谱，然后按parent首先对结果进行排序，然后按custom_order进行第二次排序。

问题：我设法获得了结果列表，但订单错误。

数据库模型

class Person(Model):
    name = CharField()
    parent = ForeignKeyField('self', backref='children', null = True) 
    custom_order = FloatField()

注意：如果parent字段为空，则为根项目

查询代码

# Define the base case of our recursive CTE. This will be people that have a null parent foreign-key.
Base = Person.alias()
base_case = (Base
    .select(Base)
    .where(Base.parent.is_null())
    .cte('base', recursive=True))

# Define the recursive terms.
RTerm = Person.alias()
recursive = (RTerm
    .select(RTerm)
    .join(base_case, on=(RTerm.parent == base_case.c.id)))

# The recursive CTE is created by taking the base case and UNION ALL with the recursive term.
cte = base_case.union_all(recursive)

# We will now query from the CTE to get the people
query = cte.select_from(cte.c.id, cte.c.name, cte.c.parent_id, cte.c.custom_order).order_by(cte.c.parent_id, cte.c.custom_order)

print(query.sql())

打印查询语法

('WITH RECURSIVE "base" AS 
(
SELECT "t1"."id", "t1"."name", "t1"."parent_id", "t1"."custom_order" FROM "person" AS "t1" WHERE ("t1"."parent_id" IS ?) 
UNION ALL 
SELECT "t2"."id", "t2"."name", "t2"."parent_id", "t2"."custom_order" FROM "person" AS "t2" INNER JOIN "base" ON ("t2"."parent_id" = "base"."id")
) 
SELECT "base"."id", "base"."name", "base"."parent_id" FROM "base" 
ORDER BY "base"."parent_id", "base"."custom_order"', 
[None])

Answer 1

问题根源问题中发布的代码可以正常工作。我通过将查询结果打印到控制台来验证它：

query = cte.select_from(cte.c.id, cte.c.name, cte.c.parent_id, cte.c.custom_order).order_by(cte.c.parent_id, cte.c.custom_order).dicts()
print(json.dumps(list(query), indent=4))

问题源于以下事实：我在将查询结果打印到控制台之前将查询结果传递给嵌套的python Dictionary，但Python Dictionary为无序。因此，难怪打印结果的顺序与数据库结果的顺序不同。

解决方案如果要以固定顺序存储查询结果，请使用Python Ordered Dictionary：

import collections
treeDictionary = collections.OrderedDict()