peewee 选择在使用模型实例而不是直接使用模型时不起作用的地方 [英] peewee select where not working when using a model instance rather than a model directly

问题描述

我有一个 peewee 模型 my_table = MyTable() 的实例，我想从中选择一些模型实例.

我不明白为什么会这样:

在 [0] [selection.p_name for selection in my_table.select() if selection.p_type == "Solar"]Out [0] ['太阳能，光伏'，'太阳能，光伏'，'太阳能，光伏'，'太阳能，光伏'，'太阳能，聚光太阳能'，'太阳能，聚光太阳能']

但这不是:

在 [1] selections = my_table.select().where(my_table.p_type=="Solar")在 [2] [t.p_name for t in selection]出 [2]

什么都没有输出.事实上，len(selections)=0

我做错了什么吗?

我的模型定义在一个文件中，如下所示:

cafe3db = SqliteDatabase(db_fp)类 Cafe3BaseModel(模型):元类:数据库 = cafe3db类场景表(Cafe3BaseModel):path_scenario_key = CharField(primary_key=True)path_type = CharField()路径名称 = CharField()cafe3db.create_tables([ScenarioTable])

然后我填充表格.这是 SQLite 数据库的屏幕截图，如 SQLite 的 DB Browswer 所示:

然后我创建表的一个实例:场景表 = 场景表()

然后，在 Python shell 中，我导入实例:

from x.y import script_table

我知道它拥有我期望的所有模型实例 (112):

<预><代码>>>>len(scenario_table.select())112

这有效:

<预><代码>>>>[t.pathway_name for t in scene_table.select() if t.pathway_type == 'Coal']['煤，亚烟'，'煤，烟'，'煤，褐煤'，'煤，亚烟'，'煤，褐煤'，'煤，烟'，'煤，烟'，'煤，褐煤']

但这不是:

<预><代码>>>>[t.pathway_name for t in scene_table.select().where(scenario_table.pathway_type == 'Coal')][]

经过反复试验，我能够通过直接导入模型而不是模型的实例来使事情发挥作用.所以，而不是:

 from x.y import script_table

我现在有:

 from x.y import ScenarioTable

现在:

selections = ScenarioTable.select().where(ScenarioTable.pathway_type=='Coal')[t.pathway_name for t in selection]

确实返回预期的模型实例名称列表.

所以我现在的问题是:为什么模型实例 select 起作用，而模型实例 where 不起作用?

解决方案

我正在尝试重现您的问题，但我不能.

首先我创建数据库和表:

导入peeweedb = peewee.SqliteDatabase('test.db')数据库连接()类 my_table(peewee.Model):p_name = peewee.CharField()p_type = peewee.CharField()元类:数据库 = dbdb.create_tables([my_table])

然后我插入两行:

d1 = my_table(p_name="太阳能、光伏", p_type="太阳能")d1.save()d2 = my_table(p_name="风车", p_type="风")d2.save()

然后我尝试你的命令:

<预><代码>>>>[t.p_name for t in my_table.select().where(my_table.p_type=="Solar")]['太阳能、光伏']

所以它在这里工作 - 也许你做错了什么，但你提供的代码是正确的

I have an instance of a peewee Model my_table = MyTable() from which I want to select some model instances.

I don't understand why this works:

In  [0] [selection.p_name for selection in my_table.select() if selection.p_type == "Solar"] 
Out [0] ['Solar, photovoltaic',
         'Solar, photovoltaic',
         'Solar, photovoltaic',
         'Solar, photovoltaic',
         'Solar, concentrated solar power',
         'Solar, concentrated solar power']

but this doesn't:

In  [1] selections = my_table.select().where(my_table.p_type=="Solar")
In  [2] [t.p_name for t in selections]
Out [2] 

Nothing is output. In fact, len(selections)=0

Am I doing something wrong?

My model definition is in one file and is as follows:

cafe3db = SqliteDatabase(db_fp)

class Cafe3BaseModel(Model):
    class Meta:
        database = cafe3db
class ScenarioTable(Cafe3BaseModel):
    pathway_scenario_key = CharField(primary_key=True)
    pathway_type = CharField()
    pathway_name = CharField()

cafe3db.create_tables([ScenarioTable])

I then populate the tables. Here is a screen capture of the SQLite database as seen DB Browswer for SQLite:

I then create an instance of the table: scenario_table = ScenarioTable()

Then, in a Python shell, I import the instance:

from x.y import scenario_table

I know it has all the model instances I expect (112):

>>> len(scenario_table.select())
112

And this works:

>>> [t.pathway_name for t in scenario_table.select() if t.pathway_type == 'Coal']
['Coal, sub-bituminous', 'Coal, bituminous', 'Coal, lignite', 'Coal, sub-bituminous', 'Coal, lignite', 'Coal, bituminous', 'Coal, bituminous', 'Coal, lignite']

But this doesn't:

>>> [t.pathway_name for t in scenario_table.select().where(scenario_table.pathway_type == 'Coal')]
[]

After trial and error, I was able to make things work by importing the model directly rather than an instance of the model. So, rather than:

    from x.y import scenario_table

I now have:

    from x.y import ScenarioTable  

and now:

selections = ScenarioTable.select().where(ScenarioTable.pathway_type=='Coal')
[t.pathway_name for t in selections]    

Does return the expected list of model instance names.

So my question is now: why does the model instance select work, but not the model instance where?

解决方案

I'm trying to reproduce your problem, but I can't.

First I create the database and the table:

import peewee
db = peewee.SqliteDatabase('test.db')
db.connect()

class my_table(peewee.Model):
    p_name = peewee.CharField()
    p_type = peewee.CharField()

    class Meta:
        database = db
db.create_tables([my_table])

Then I insert two rows:

d1 = my_table(p_name="Solar, photovoltaic", p_type="Solar")
d1.save()
d2 = my_table(p_name="Windmill", p_type="Wind")
d2.save()

After that I try your command:

>>> [t.p_name for t in my_table.select().where(my_table.p_type=="Solar")]
['Solar, photovoltaic']

So it works here - maybe you're doing something else wrong, but the code you provided is correct

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