Django version: 3.1.0, MySQL backend
I have a JSONField on my model:
class Employee(models.Model):
address = models.JSONField(
encoder=AddressEncoder,
dedocer=AddressDecoder,
default=address_default
)
Then the encoder looks like this:
class AddressEncoder(DjangoJSONEncoder):
def default(self, o):
if isinstance(o, Address):
return dataclasses.asdict(o)
raise TypeError("An Address instance is required, got an {0}".format(type(o)))
Then the address_default looks like this:
def address_default():
encoder = AddressEncoder()
address = Addres(...)
return encoder.encode(address)
Currently I have set the address_default to return a dict. Although it should actually return an Address instance. When I change this so that the address_default returns an instance of Address, an error is raised TypeError: Object of type Address is not JSON serializable. However, in other parts of the code where the address is in fact an instance of Address, no errors are raised. So the custom AddressEncoder does not seem to be used on the value provided by the address_default.
When the address attribute on Employee is set to e.g. a string, no error is thrown. This might have to do with what is explained in Why is Django not using my custom encoder class. The code in AddressEncoder is not executed.
Question:
What is the correct way to set up the address_default, and Encoder/Decoder so that the address attribute can be, and only be, an instance of Address?
I solved the problem. It had to do with my migrations. One of my migrations contained a definition of the address-field without the encoders. Hence changing the address_default to return a non json serializable object throws the corresponding error.
I had to manually find and change that migrations so that the definition of the address field includes the custom encoder.
The check isinstance(self.address, Address) is then done in an overridden save() method on the Employee model.
Related
I'd like to automate as much as possible the instantiation of an ILA directly from the Chisel code. This means instantiating a module that looks like this:
i_ila my_ila(
.clk(clock),
.probe0(a_signal_to_monitor),
.probe1(another_signal_to_monitor),
// and so on
);
I'm planning to store the signals that I want to monitor in a list of UInt so that at the end of module elaboration I can generate the instantiation code above, which I will copy/paste in the final Verilog code (or write a Python script that does that automatically).
First, is there a better way of doing this, perhaps at the level of FIRRTL?
Even if I go with this semi-manual approach, I need to know what would be the name of the signals in the final Verilog, which is not necessarily the name of the UInt vals in the code (and which, besides, I don't know how to get automatically without having to retype the name of the variable as a string somewhere). How can I get them?
I'd like to provide a more complete example, but I wanted to make sure to at least write something up. This also needs to be fleshed out as a proper example/tutorial on the website.
FIRRTL has robust support for tracking names of signals across built-in and custom transformations. This is a case where the infrastructure is all there, but it's very much a power user API. In short, you can create FIRRTL Annotations that will track Targets. You can then emit custom metadata files or use the normal FIRRTL annotation file (try the CLI option -foaf / --output-annotation-file).
An example FIRRTL Annotation that has will emit a custom metadata file at the end of compilation:
// Example FIRRTL annotation with Custom serialization
// FIRRTL will track the name of this signal through compilation
case class MyMetadataAnno(target: ReferenceTarget)
extends SingleTargetAnnotation[ReferenceTarget]
with CustomFileEmission {
def duplicate(n: ReferenceTarget) = this.copy(n)
// API for serializing a custom metadata file
// Note that multiple of this annotation will collide which is an error, not handled in this example
protected def baseFileName(annotations: AnnotationSeq): String = "my_metadata"
protected def suffix: Option[String] = Some(".txt")
def getBytes: Iterable[Byte] =
s"Annotated signal: ${target.serialize}".getBytes
}
The case class declaration and duplicate method are enough to track a single signal through compilation. The CustomFileEmission and related baseFileName, suffix, and getBytes methods define how to serialize my custom metadata file. As mentioned in the comment, as implemented in this example we can only have 1 instance of this MyMetadataAnno or they will try to write the same file which is an error. This can be handled by customizing the filename based on the Target, or writing a FIRRTL transform to aggregate multiple of this annotation into a single annotation.
We then need a way to create this annotation in Chisel:
def markSignal[T <: Data](x: T): T = {
annotate(new ChiselAnnotation {
// We can't call .toTarget until end of Chisel elaboration
// .toFirrtl is called by Chisel at the end of elaboration
def toFirrtl = MyMetadataAnno(x.toTarget)
})
x
}
Now all we need to do is use this simple API in our Chisel
// Simple example with a marked signal
class Foo extends MultiIOModule {
val in = IO(Flipped(Decoupled(UInt(8.W))))
val out = IO(Decoupled(UInt(8.W)))
markSignal(out.valid)
out <> in
}
This will result in writing the file my_metadata.txt to the target directory with the contents:
Annotated signal: ~Foo|Foo>out_valid
Note that this is special FIRRTL target syntax saying that out_valid is the annotated signal that lives in module Foo.
Complete code in an executable example:
https://scastie.scala-lang.org/moEiIqZPTRCR5mLQNrV3zA
We are working on a Top-Down-RPG-like Multiplayer game for learning purposes (and fun!) with some friends. We already have some Entities in the Game and Inputs are working, but the network implementation gives us headache :D
The Issues
When trying to convert with dict some values will still contain the pygame.Surface, which I dont want to transfer and it causes errors when trying to jsonfy them. Other objects I would like to transfer in a simplyfied way like Rectangle cannot be converted automatically.
Already functional
Client-Server connection
Transfering JSON objects in both directions
Async networking and synchronized putting into a Queue
Situation
A new player connects to the server and wants to get the current game state with all objects.
Data-Structure
We use a "Entity-Component" based architecture, so we separated the game logic very strictly into "systems", while the data is stored in the "components" of each Entity. The Entity is a very simple container and has nothing more than a ID and a list of components. Example Entity (shorten for better readability):
Entity
|-- Component (Moveable)
|-- Component (Graphic)
| |- complex datatypes like pygame.SURFACE
| `- (...)
`- Component (Inventory)
We tried different approaches, but all seems not to fit very well or feel "hacky".
pickle
Very Python near, so not easy to implement other clients in future. And I´ve read about some security risks when creating items from network in this dynamic way how pickle it offers. It does not even solve the Surface/Rectangle issue.
__dict__
Still contains the reference to the old objects, so a "cleanup" or "filter" for unwanted datatypes happens also in the origin. A deepcopy throws Exception.
...\Python\Python36\lib\copy.py", line 169, in deepcopy
rv = reductor(4)
TypeError: can't pickle pygame.Surface objects
Show some code
The method of the "EnitityManager" Class which should generate the Snapshot of all Entities, including their components. This Snapshot should be converted to JSON without any errors - and if possible without much configuration in this core-class.
class EnitityManager:
def generate_world_snapshot(self):
""" Returns a dictionary with all Entities and their components to send
this to the client. This function will probably generate a lot of data,
but, its to send the whole current game state when a new player
connects or when a complete refresh is required """
# It should be possible to add more objects to the snapshot, so we
# create our own Snapshot-Datastructure
result = {'entities': {}}
entities = self.get_all_entities()
for e in entities:
result['entities'][e.id] = deepcopy(e.__dict__)
# Components are Objects, but dictionary is required for transfer
cmp_obj_list = result['entities'][e.id]['components']
# Empty the current list of components, its going to be filled with
# dictionaries of each cmp which are cleaned for the dump, because
# of the errors directly coverting the whole datastructure to JSON
result['entities'][e.id]['components'] = {}
for cmp in cmp_obj_list:
cmp_copy = deepcopy(cmp)
cmp_dict = cmp_copy.__dict__
# Only list, dict, int, str, float and None will stay, while
# other Types are being simply deleted including their key
# Lists and directories will be cleaned ob recursive as well
cmp_dict = self.clean_complex_recursive(cmp_dict)
result['entities'][e.id]['components'][type(cmp_copy).__name__] \
= cmp_dict
logging.debug("EntityMgr: Entity#3: %s" % result['entities'][3])
return result
Expectation and actual results
We can find a way to manually override elements which we dont want. But as the list of components will increase we have to put all the filter logic into this core class, which should not contain any components specializations.
Do we really have to put all the logic into the EntityManager for filtering the right objects? This does not feel good, as I would like to have all convertion to JSON done without any hardcoded configuration.
How to convert all this complex data in a most generic approach?
Thanks for reading so far and thank you very much for your help in advance!
Interesting articles which we were already working threw and maybe helpful for others with similar issues
https://gafferongames.com/post/what_every_programmer_needs_to_know_about_game_networking/
http://code.activestate.com/recipes/408859/
https://docs.python.org/3/library/pickle.html
UPDATE: Solution - thx 2 sloth
We used a combination of the following architecture, which works really great so far and is also good to maintain!
Entity Manager now calls the get_state() function of the entity.
class EntitiyManager:
def generate_world_snapshot(self):
""" Returns a dictionary with all Entities and their components to send
this to the client. This function will probably generate a lot of data,
but, its to send the whole current game state when a new player
connects or when a complete refresh is required """
# It should be possible to add more objects to the snapshot, so we
# create our own Snapshot-Datastructure
result = {'entities': {}}
entities = self.get_all_entities()
for e in entities:
result['entities'][e.id] = e.get_state()
return result
The Entity has only some basic attributes to add to the state and forwards the get_state() call to all the Components:
class Entity:
def get_state(self):
state = {'name': self.name, 'id': self.id, 'components': {}}
for cmp in self.components:
state['components'][type(cmp).__name__] = cmp.get_state()
return state
The components itself now inherit their get_state() method from their new superclass components, which simply cares about all simple datatypes:
class Component:
def __init__(self):
logging.debug('generic component created')
def get_state(self):
state = {}
for attr, value in self.__dict__.items():
if value is None or isinstance(value, (str, int, float, bool)):
state[attr] = value
elif isinstance(value, (list, dict)):
# logging.warn("Generating state: not supporting lists yet")
pass
return state
class GraphicComponent(Component):
# (...)
Now every developer has the opportunity to overlay this function to create a more detailed get_state() function for complex types directly in the Component Classes (like Graphic, Movement, Inventory, etc.) if it is required to safe the state in a more accurate way - which is a huge thing for maintaining the code in future, to have these code pieces in one Class.
Next step is to implement the static method for creating the items from the state in the same Class. This makes this working really smooth.
Thank you so much sloth for your help.
Do we really have to put all the logic into the EntityManager for filtering the right objects?
No, you should use polymorphism.
You need a way to represent your game state in a form that can be shared between different systems; so maybe give your components a method that will return all of their state, and a factory method that allows you create the component instances out of that very state.
(Python already has the __repr__ magic method, but you don't have to use it)
So instead of doing all the filtering in the entity manager, just let him call this new method on all components and let each component decide that the result will look like.
Something like this:
...
result = {'entities': {}}
entities = self.get_all_entities()
for e in entities:
result['entities'][e.id] = {'components': {}}
for cmp in e.components:
result['entities'][e.id]['components'][type(cmp).__name__] = cmp.get_state()
...
And a component could implement it like this:
class GraphicComponent:
def __init__(self, pos=...):
self.image = ...
self.rect = ...
self.whatever = ...
def get_state(self):
return { 'pos_x': self.rect.x, 'pos_y': self.rect.y, 'image': 'name_of_image.jpg' }
#staticmethod
def from_state(state):
return GraphicComponent(pos=(state.pos_x, state.pos_y), ...)
And a client's EntityManager that recieves the state from the server would iterate for the component list of each entity and call from_state to create the instances.
Can I map Scala functions to JSON; or perhaps via a different way than JSON?
I know I can map data types, which is fine. But I'd like to create a function, map it to JSON send it via a REST method to another server, then add that function to a list of functions in another application and apply it.
For instance:
def apply(f: Int => String, v: Int) = f(v)
I want to make a list of functions that can be applied within an application, over different physical locations. Now I want to add and remove functions to the list. By means of REST calls.
Let's assume I understand security problems...
ps.. If you downvote, you might as well have the decency to explain why
If I understand correctly, you want to be able to send Scala code to be executed on different physical machines. I can think of a few different ways of achieving that
Using tools for distributed computing e.g. Spark. You can set up Spark clusters on different machines and then select to which cluster you want to submit Spark jobs. There are a lot of other tools for distributed computing that might also be worth looking into.
Pass scala code as a string and compile it either within your server side code (here's an example) or by invoking scalac as an external process.
Send the functions as byte code and execute the byte code on the remote machine.
If it fits with what you want to do, I'd recommend option #1.
Make sure that you can really trust the code that you want to execute, to not expose yourself to malicious code.
The answer is you can't do this, and even if you could you shouldn't!
You should never, never, never write a REST API that allows the client to execute arbitrary code in your application.
What you can do is create a number of named operations that can be executed. The client can then pass the name of the operation which the server can look up in a Map[String, <function>] and execute the result.
As mentioned in my comment, here is an example of how to turn a case class into JSON. Things to note: don't question the implicit val format line (it's magic); each case class requires a companion object in order to work; if you have Optional fields in your case class and define them as None when turning it into JSON, those fields will be ignored (if you define them as Some(whatever), they will look like any other field). If you don't know much about Scala Play, ignore the extra stuff for now - this is just inside the default Controller you're given when you make a new Project in IntelliJ.
package controllers
import javax.inject._
import play.api.libs.json.{Json, OFormat}
import play.api.mvc._
import scala.concurrent.Future
#Singleton
class HomeController #Inject()(cc: ControllerComponents) extends AbstractController(cc) {
case class Attributes(heightInCM: Int, weightInKG: Int, eyeColour: String)
object Attributes {
implicit val format: OFormat[Attributes] = Json.format[Attributes]
}
case class Person(name: String, age: Int, attributes: Attributes)
object Person {
implicit val format: OFormat[Person] = Json.format[Person]
}
def index: Action[AnyContent] = Action.async {
val newPerson = Person("James", 24, Attributes(192, 83, "green"))
Future.successful(Ok(Json.toJson(newPerson)))
}
}
When you run this app with sbt run and hit localhost:9000 through a browser, the output you see on-screen is below (formatted for better reading). This is also an example of how you might send JSON as a response to a GET request. It isn't the cleanest example but it works.
{
"name":"James",
"age":24,
"attributes":
{
"heightInCM":187,
"weightInKG":83,
"eyeColour":"green"
}
}
Once more though, I would never recommend passing actual functions between services. If you insist though, maybe store them as a String in a Case Class and turn it into JSON like this. Even if you are okay with passing functions around, it might even be a good exercise to practice security by validating the functions you receive to make sure they're not malicious.
I also have no idea how you'll convert them back into a function either - maybe write the String you receive to a *.scala file and try to run them with a Bash script? Idk. I'll let you figure that one out.
In my PostgreSQL database I have:
CREATE TABLE category (
// ...
category_name_localization JSON not null,
);
In Java, I have a JDO class like so:
#javax.jdo.annotations.PersistenceCapable(table = "category" )
public class Category extends _BlueEntity implements Serializable {
//...
private org.json.simple.JSONObject category_name_localization;
#javax.jdo.annotations.Column( name = "category_name_localization" )
public org.json.simple.JSONObject getCategoryNameLocalization() {
return category_name_localization;
}
}
When I use this class, DataNucleus gives the following exception:
org.datanucleus.exceptions.NucleusUserException: Field "com.advantagegroup.blue.ui.entity.Category.category_name_localization" is a map that has been specified without a join table and neither the key nor the value has a mapped-by specified. This is invalid!
at org.datanucleus.store.rdbms.RDBMSStoreManager.newJoinTable(RDBMSStoreManager.java:2720)
at org.datanucleus.store.rdbms.mapping.java.AbstractContainerMapping.initialize(AbstractContainerMapping.java:82)
at org.datanucleus.store.rdbms.mapping.MappingManagerImpl.getMapping(MappingManagerImpl.java:680)
at org.datanucleus.store.rdbms.table.ClassTable.manageMembers(ClassTable.java:518)
at org.datanucleus.store.rdbms.table.ClassTable.manageClass(ClassTable.java:424)
at org.datanucleus.store.rdbms.table.ClassTable.initializeForClass(ClassTable.java:1250)
at org.datanucleus.store.rdbms.table.ClassTable.initialize(ClassTable.java:271)
at org.datanucleus.store.rdbms.RDBMSStoreManager$ClassAdder.initializeClassTables(RDBMSStoreManager.java:3288)
at org.datanucleus.store.rdbms.RDBMSStoreManager$ClassAdder.run(RDBMSStoreManager.java:2897)
at org.datanucleus.store.rdbms.AbstractSchemaTransaction.execute(AbstractSchemaTransaction.java:118)
at org.datanucleus.store.rdbms.RDBMSStoreManager.manageClasses(RDBMSStoreManager.java:1637)
at org.datanucleus.store.rdbms.RDBMSStoreManager.getDatastoreClass(RDBMSStoreManager.java:665)
at org.datanucleus.store.rdbms.RDBMSStoreManager.getPropertiesForGenerator(RDBMSStoreManager.java:2098)
at org.datanucleus.store.AbstractStoreManager.getStrategyValue(AbstractStoreManager.java:1278)
at org.datanucleus.ExecutionContextImpl.newObjectId(ExecutionContextImpl.java:3668)
at org.datanucleus.state.StateManagerImpl.setIdentity(StateManagerImpl.java:2276)
at org.datanucleus.state.StateManagerImpl.initialiseForPersistentNew(StateManagerImpl.java:482)
at org.datanucleus.state.StateManagerImpl.initialiseForPersistentNew(StateManagerImpl.java:122)
at org.datanucleus.state.ObjectProviderFactoryImpl.newForPersistentNew(ObjectProviderFactoryImpl.java:218)
at org.datanucleus.ExecutionContextImpl.persistObjectInternal(ExecutionContextImpl.java:1986)
at org.datanucleus.ExecutionContextImpl.persistObjectWork(ExecutionContextImpl.java:1830)
at org.datanucleus.ExecutionContextImpl.persistObject(ExecutionContextImpl.java:1685)
at org.datanucleus.api.jdo.JDOPersistenceManager.jdoMakePersistent(JDOPersistenceManager.java:712)
at org.datanucleus.api.jdo.JDOPersistenceManager.makePersistent(JDOPersistenceManager.java:738)
at com.advantagegroup.blue.ui.jdo._BlueJdo.insert(_BlueJdo.java:40)
at ...
This error makes sense in a way, because org.json.simple.JSONObject extends Map. However, this field is not part of any relationships -- it is of type JSON and therefore it is natural to back it with JSONObject
How do I tell JDO / DataNucleus to chill and treat org.json.simple.JSONObject the same way it would a String or a Date?
Thanks!
DC
My understanding of this is that your default attempt is trying to persist a normal Map (since while it doesnt know what a JSONObject is, it does know what a Map is), and it will need a join table for that for RDBMS.
Since you presumably want the JSONObject persisted into a single column then you need to create a JDO AttributeConverter. I've done similar things with my own types and it works fine (i'm on v5.0.5 IIRC).
I also found this in their docs, for when you have your own Map class that it doesn't know how to handle by default in terms of replacing it with a proxy (to intercept the calls to put, putAll etc). If you add that line it will not try to wrap this field with a proxy (which it doesn't know how to do for that type, unless you tell it). If you wanted to auto-detect the JSONObject becoming "dirty" you would need to write a proxy wrapper, as per this page.
This doesn't answer how to map the column for that converter to use a "json" type in PostgreSQL, but i'd guess that if you set the sqlType you may get success in that respect.
In a Django application, I'm trying to access an existing MySQL database created with Hibernate (a Java ORM). I reverse engineered the model using:
$ manage.py inspectdb > models.py
This created a nice models file from the Database and many things were quite fine. But I can't find how to properly access boolean fields, which were mapped by Hibernate as columns of type BIT(1).
The inspectdb script by default creates these fields in the model as TextField and adds a comment saying that it couldn't reliably obtain the field type. I changed these to BooleanField but and opened my model objects using the admin, but it doesn't work (the model objects always fetch a value of true for these fields). Using IntegerField won't work as well (e.g. in the admin these fields show strange non-ascii characters).
Any hints of doing this without changing the database? (I need the existing Hibernate mappings and Java application to still work with the database).
Further info: I left these fields as BooleanField and used the interactive shell to look at the fetched values. They are returned as '\x00' (when Java/Hibernate value is false) and '\x01' (when true), instead of Python boolean values "True" and "False".
>>> u = AppUser.objects.all()[0]
>>> u.account_expired
'\x00'
>>> u.account_enabled
'\x01'
Where the model includes:
class AppUser(models.Model):
account_expired = models.BooleanField()
account_enabled = models.BooleanField(blank=True)
# etc...
This is the detailed solution from Dmitry's suggestion:
My derived field class:
class MySQLBooleanField(models.BooleanField):
__metaclass__ = models.SubfieldBase
def to_python(self, value):
if isinstance(value, bool):
return value
return bytearray(value)[0]
def get_db_prep_value(self, value):
return '\x01' if value else '\x00'
Fields in my model:
account_enabled = MySQLBooleanField()
account_expired = MySQLBooleanField()
I had to deal the same problem, but rather than subclassing the field, I extended the MySQL backend to understand the Hibernate way. It's only a few lines of code and has the advantage that the DB introspection can be made to work correctly, as well.
See it here.
hibernateboolsbackend / backends / mysql / base.py
# We want to import everything since we are basically subclassing the module.
from django.db.backends.mysql.base import *
django_conversions.update({
FIELD_TYPE.BIT: lambda x: x != '\x00',
})
DatabaseIntrospection.data_types_reverse.update({
FIELD_TYPE.BIT: 'BooleanField',
})
The django-mysql package provides a BooleanField subclass called Bit1BooleanField that solves this:
from django.db import Model
from django_mysql.models import Bit1BooleanField
class AppUser(Model):
bit1bool = Bit1BooleanField()
Easier than rolling your own, and tested on several Django and Python versions.
I guess that only way is to subclass, say, BooleanField, and override to_python/get_prep_value functions, so the field works seamlessly with django and
your db.
To make it work on django 1.7.1 i've to change the "to_python" function because it was not working to read correctly the data from the db:
def to_python(self, value):
if value in (True, False): return value
if value in ('t', 'True', '1', '\x01'): return True
if value in ('f', 'False', '0', '\x00'): return False
In Python Boolean type is a subclass of integer But whereas Java it is of type Bit.
So in DB for Python Boolean field datatype should be Tinyint instead of BIT type.
Due to the above reason the application behaving unexpectedly returning \x00 and \x01 value.
If we add a boolean field in Django model and run the migration then migrate, It will add a column of type Tinyint instead of bit.
So updating the column type to Tinyint should resolve the issue.