Oh

you check Message.feed_entry and Message.link.feed_entry relationships

This is so short. I guess I was thinking way to complex

each instance of Message can have one of those two relationships, right?

Yep

so you need to select the messages where one of the related FeedEntry instances has the status equal to 'UNREAD'

And it won't get None errors on m.feed_entry.*?

Nope

it will select only those messages, which have this relationship

Or right it is translating it first. So not real python properties. Always forget that.

Cool

Many thanks!

Or right it is translating it first. So not real python properties. Always forget that.

correct)

Many thanks!

you are welcome)

I assume FeedEntry[1] is the FeedEntry with ID 1?

AFAIK it could be any primary key

AFAIK it could be any primary key

Correct, this was an example of extracting an instance of FeedEntry. You could retirew it in any other way, for example using FeedEntry.get() https://docs.ponyorm.com/api_reference.html#Entity.get

Guys it looks like questions like this could be collected on a special web page with the answers and examples

This would be very handy

Guys it looks like questions like this could be collected on a special web page with the answers and examples

There is such a place https://docs.ponyorm.com/working_with_entity_instances.html

Hi is talking about community provided faq I guess

Hi is talking about community provided faq I guess

something like that. this page looks a bit tutorialish

may be a wiki or something like that

or... this is great and hacky:) you may post questions on StackOverflow and answer them, even if they wasn't originally asked there

this will allow to google an answer and spread PonyORM on SO at the same time:)

this will allow to google an answer and spread PonyORM on SO at the same time:)

Good catch)

@lig11 You just want to create stackoverflow

oh, I miss “you may post questions on StackOverflow and answer them”

Use the github wiki?

Welcome!

Hi guys!

To guys

Really happy to join you all

Welcome

Thanks buddy

Hey guys I have a problem with the display of the ORM online editor. I found no good place to file an issue, so I went for the doc repo: https://github.com/ponyorm/pony-doc/issues/1

hey right, we are going to fix that and probably create a space for the Editor bugs

Ive seen empty repos with a readme for that kind of usecase before.

ok

Thank you for reporing about the bug, Luckydonald!

You're welcome :D

Do you guys have a clue what AttributeError: _session_cache_ could mean?

This is my DBInitMessage class https://github.com/luckydonald/pbft/blob/953d74f86258603be0a5b06824d92130af9849e8/code/db_proxy/database.py#L41

And this is messages.InitMessage https://github.com/luckydonald/pbft/blob/953d74f86258603be0a5b06824d92130af9849e8/code/node/messages.py#L57

Do you guys have a clue what AttributeError: _session_cache_ could mean?

https://github.com/luckydonald/pbft/blob/953d74f86258603be0a5b06824d92130af9849e8/code/db_proxy/main.py#L22

Wait a sec...

I think the problem is in the fact that Entity.__init__ method was not called I think you need to add super(Message, self).__init__() at the beginning of the Message.__init__ method

Because the Message class is a mixin

I think it is better to not define __init__ in your mixins at all, and don't have any additional attributes which are unknown to Pony. This is because an entity instance can be constructed in several completely different situations. One thing is when you create a new instance, but completely different story is when an instance is retrieved from the database. In that case instance initialization works in a different way, and by overriding __init__ you may broke internal logic

AFAK it is recomended way of naming in Python to use Mixin word in such a classes like class MessageMixin:

So I made a mixin, I didn't know :D I just have this InitMessage class, and want to dump it into a Database, but without modifying the original class. I'll try the super()

The DBInitMessage is subclassing messages.InitMessage and db.Entity, to have InitMessage instances which can be stored in a DB

Because the Message class is a mixin

I belive DBInitMessage would be the mixin, adding the database parts to InitMessage

Updated images above with links to github

I have the Message classes which already do stuff like building itself from json, and converting itself to json, for sending and receiving. I now want a second program to additionally store them in a database. To avoid to write all json-related stuff twice, it is just importing the Message classes from the first program. So my idea was to make a subclass with the pony foo = Required stuff. Any thoughts how I could realize that?

Because the Message class is a mixin

So, Message is not really supposed to be a mixin, because it still is a stand-alone class...

Oh, now I think I understand. class A(object): def __init__(self): super().__init__() print("Inside class A init") class B(object): def __init__(self): print("Inside class B init") class C(A,B): def __init__(self): super().__init__() print("Inside class C init") So: >>> C() Inside class B init Inside class A init Inside class C init

I think the problem is in the fact that Entity.__init__ method was not called I think you need to add super(Message, self).__init__() at the beginning of the Message.__init__ method

Stupid me. Of course I can add super().__init__() to A() (=Message()), because it just calls object.__init__() if there is no other class.

I think it is more complex than that, if __init__ method expects some arguments

Oh, now I think I understand. class A(object): def __init__(self): super().__init__() print("Inside class A init") class B(object): def __init__(self): print("Inside class B init") class C(A,B): def __init__(self): super().__init__() print("Inside class C init") So: >>> C() Inside class B init Inside class A init Inside class C init

Thats wrong. The print was after the init, so that may be more confusing as it helps

class A(object): def __init__(self, foobar): print("Inside class A init, foobar={}".format(foobar)) super().__init__() print("After class A init, foobar={}".format(foobar)) class B(object): def __init__(self): print("Inside class B init") super().__init__() print("After class B init") class C(A, B): def __init__(self): print("Inside class C init") super().__init__("hey") print("After class C init") So: In[33]: C() Inside class C init Inside class A init, foobar=hey Inside class B init After class B init After class A init, foobar=hey After class C init Out[33]: <__main__.C at 0x1095c1780>

I prefer something like that: class JsonMixin(object): def to_json(self): return {'type': self.type, 'value': self.value} @classmethod def from_json(cls, **kwargs): return cls(**kwargs) class Message(JsonMixin): def __init__(self, type, value): self.type = type self.value = value class DBMessage(JsonMixin, db.Entity): type = Required(int) value = Required(str) This way we have two different classes Message and DBMessage. Message is for in-memory data, and DBMessage is for persistent data. The common Json functionality is placed inside separate mixin class which have no __init__ method

I see

Other question, how can I model this correctly:

https://editor.ponyorm.com/user/luckydonald/pbft

I get errors like: pony.orm.core.ERDiagramError: Attribute DBPrevoteMessage.value conflicts with attribute DBInitMessage.value because both entities inherit from DBMessage. To fix this, move attribute definition to base class

But If i move value up to DBMessage that would mean DBProposeMessage has that too.

You need to add the 'value' and 'node' attributes to the DBMessage entity and remove tnem from the descendand classes

And set it to optional?

yes

or, create another entity in the middle of the hierarchy and inherit from it the entities that have this attribute

but we have node, leader, value (VoteMessage) node, leader, (ProposeMessage) node, value (InitMessage) So inheration is not really possible, right?

if you make them optional, it would work

okey

KeyError: ?.?

🔨 1 new commits to pbft:master: 03dea8e: db proxy Database with mixins? by luckydonald

KeyError: ?.?

Now I am puzzled.

I just tried to remove the DBMessage top class, and added the stuff via mixins instead, I just learend about :D

It seems that Entity.__init__ call was still missed

But I'm not overriding that any more