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

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

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

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

You defined __init__ in your mixin and not call base __init__

I will rewrite it as one big class.

In my test all works as expected: from pony.orm import * class PersonMixin(object): def hello(self): print('My name is ' + self.name) class Person(PersonMixin): def __init__(self, name): self.name = name db = Database('sqlite', ':memory:') class DBPerson(PersonMixin, db.Entity): name = Required(str) sql_debug(True) db.generate_mapping(create_tables=True) with db_session: p1 = Person(name='John') p1.hello() p2 = DBPerson(name='Mike') p2.hello() with db_session: p3 = select(p for p in DBPerson).first() p3.hello()

Let me explain my project a bit, maybe that will help understanding my problem. I have a script (called node) which sends (broadcasts) messages and receives brodcasted messages. Thats basically all it does. Receiving messages and doing a bit of calulation what to send next. And I am writing another script (called db_proxy) which also reveives the broadcasted messages. This script should decode the stuff from the socket, like the node, but put it in a database. So I want to use the same code for receiving the Messages. But in second program i want to dump it into a database, instead of answering with more messages. The mixin, while perfectly working, is not as readable, because the functionality is split into 2 classes. I think I will write seperate DBMessage class which has functions to set it's own values according to a given Message instance. with db_session: p3 = select(p for p in DBPerson).first() p = p3.from_db() # eventually calls Person(foo=self.foo, bar=self.bar) p.foo.do_stuff() With that I don't have to modify the original classes ( Message or in your example Person)

Because If you take the DB part away, the Mixin classes alone are very confusing.

I think this approach is valid. This way the code may be easier to understand

Hey guys

hey

SELECT DISTINCT ON (m.type) * FROM ( SELECT * FROM DBMessage ORDER BY date DESC ) as m ORDER BY m.type, m.date DESC This selects the newest (m.date) DBMessage of each m.type in postgres.

I can't find how to do DISTINCT on pony

Is this what you need? https://docs.ponyorm.com/api_reference.html?highlight=distinct#distinct

I couldn't find it as I searched :( Probalby, yes. Thanks

there is Quick search field here https://docs.ponyorm.com/toc.html

np

I think this is not the same thing. As I understand, "DISTINCT ON" is a special PostgreSQL construction which is not equivalent to DISTINCT

yeah, DESTINCT and DESTINCT ON ({column}) are different. https://www.postgresql.org/docs/9.0/static/sql-select.html#SQL-DISTINCT

You want to select latest message for each message type

DESTINCT removes duplicate rows, DESTINCT ON keeps only the first row with the same value of a column

You want to select latest message for each message type

Correct.

Actually I did the wrong thing, here is my correct SQL: SELECT DISTINCT ON (m.node) * FROM ( SELECT * FROM DBmessage WHERE type = 1 ) as m ORDER BY m.node, m.date DESC But lets stay by the above example :D

Can you use max id instead of a latest date to find the latest message? I think it will be a bit easier to write

Can you use max id instead of a latest date to find the latest message? I think it will be a bit easier to write

hm, probably later the max_id might not be the newest one, if a client is to slow to dump it in real time

ok, with dates you can try the following: select(m for m in DBMessage if (m.type, m.date) in select((m.type, max(m.date)) for m in DBMessage)) But if two messages of the same type may have indentical date (up to microseconds), you will get both messages

Another way is to use raw SQL query: DBMessage.select_by_sql(""" SELECT DISTINCT ON (m.node) * FROM ( SELECT * FROM DBmessage WHERE type = 1 ) as m ORDER BY m.node, m.date DESC """)

Hm, probably a db.select("sql") is better

Another way is to use raw SQL query: DBMessage.select_by_sql(""" SELECT DISTINCT ON (m.node) * FROM ( SELECT * FROM DBmessage WHERE type = 1 ) as m ORDER BY m.node, m.date DESC """)

Oh, thats even cooler!

Btw, how can I apply .show() on the resulting list?

Note that inside raw SQL you can use Python expression, which are converted to query parameters: message_type = 1 DBMessage.select_by_sql(""" SELECT DISTINCT ON (m.node) * FROM ( SELECT * FROM DBmessage WHERE type = $message_type ) as m ORDER BY m.node, m.date DESC """)

Note that inside raw SQL you can use Python expression, which are converted to query parameters: message_type = 1 DBMessage.select_by_sql(""" SELECT DISTINCT ON (m.node) * FROM ( SELECT * FROM DBmessage WHERE type = $message_type ) as m ORDER BY m.node, m.date DESC """)

I already use that, sooo cool :D

show is the method of QueryResult. select_by_sql returns list of entities, which don't have show method.

Maybe we can add it later

Okey, was just to visualize it to myself

How would I do m.date >= NOW() - '1 minute'::INTERVAL? latest_vote = orm.select(m for m in DBVoteMessage).order_by(orm.desc(DBVoteMessage.date)).first()

I want to only get messages from the last past hour. Best would be to use the server NOW()

You can write from datetime import datetime, timedelta select(m for m in DBVoteMessage if m.date >= detetime.now() - timedelta(hours=1)) But Pony will think that expression datetime.now() - timedelta(hours=1) can be evaluated in Python and replaced with a single query parameter. In order to use server NOW() you can use raw SQL fragment: select(m for m in DBVoteMessage if m.date >= raw_sql("NOW() - '1 minute'::INTERVAL"))

You can write from datetime import datetime, timedelta select(m for m in DBVoteMessage if m.date >= detetime.now() - timedelta(hours=1)) But Pony will think that expression datetime.now() - timedelta(hours=1) can be evaluated in Python and replaced with a single query parameter. In order to use server NOW() you can use raw SQL fragment: select(m for m in DBVoteMessage if m.date >= raw_sql("NOW() - '1 minute'::INTERVAL"))

timedelta lacks documentation. Only is listed as a possible type, but not how to use it.

Thanks, we'll fix it

But raw_sql is very neat. Is that executed in the same query?

yes

perfect

oops )

:D

??

Welcome!

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

Thank you for reporting, it should be fixed now. Please use the issue tracker in this project https://github.com/ponyorm/editor for any issues related to the Editor.

You are the 6th Alexander in this group oO

only 6th?