What is the difference between EmbeddedDocumentField and ReferenceField in mongoengine - json

Internally, what are the differences between these two fields? What kind of schema do these fields map to in mongo? Also, how should documents with relations be added to these fields? For example, if I use
from mongoengine import *
class User(Document):
name = StringField()
class Comment(EmbeddedDocument):
text = StringField()
tag = StringField()
class Post(Document):
title = StringField()
author = ReferenceField(User)
comments = ListField(EmbeddedDocumentField(Comment))
and call
>>> some_author = User.objects.get(name="ExampleUserName")
>>> post = Post.objects.get(author=some_author)
>>> post.comments
[]
>>> comment = Comment(text="cool post", tag="django")
>>> comment.save()
>>>
should I use post.comments.append(comment) or post.comments += comment for appending this document? My original question stems from this confusion as to how I should handle this.

EmbeddedDocumentField is just path of parent document like DictField and stored in one record with parent document in mongo.
To save EmbeddedDocument just save parent document.
>>> some_author = User.objects.get(name="ExampleUserName")
>>> post = Post.objects.get(author=some_author)
>>> post.comments
[]
>>> comment = Comment(text="cool post", tag="django")
>>> post.comment.append(comment)
>>> post.save()
>>> post.comment
[<Comment object __unicode__>]
>>> Post.objects.get(author=some_author).comment
[<Comment object __unicode__>]
See documentation: http://docs.mongoengine.org/guide/defining-documents.html#embedded-documents.

This one just a sample case where we can use embedded docs.
Lets say for example you are going to create an app that takes in requirements as they come in and save them in the db.
Now your requirement is to assign this requirement to a bunch of people each at a later stage after some processing of the requirement.
you also need to track the changes and log the activity pertaining to the processing taken place with regards to the requirement.
I know i know you might say we can use rdbms kind of relationship with refference field. but it involves in taking care of deleting obselete records in either collections which is nothing but extra code to handle the maintenance of the child collection in case of parent doc being deleted.( There are other extra efforts too that come into place ..)
instead embedded documents are stored as part of the parent doc. which Maintaining parent will involve embedded docs too.
and it will be easy to create complex json structured data using embedded docs rather than using user logic to manipulate and process the data into a complex structure.
Now Here the relation is one requirement to many handlers(which is nothing but an activity log by the handlers for the one requirement).

Related

Multiplayer game using pygame [duplicate]

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.

textX: How to generate object names with ObjectProcessors?

I have a simple example model where I would like to generate names for the objects of the Position rule that were not given a name with as <NAME>. This is needed so that I can find them later with the built-in FQN scope provider.
My idea would be to do this in the position_name_generator object processor but that will be only be called after the whole model is parsed. I don´t really understand the reason for that, since by the time I would need a Position object in the Project, the objects are already created, still the object processor will not be called.
Another idea would be to do this in a custom scope provider for Position.location which would then first do the name generation and then use the built-in FQN to find the Location object. Although this would work, I consider this hacky and I would prefer to avoid it.
What would be the textX way of solving this issue?
(Please take into account that this is only a small example. In reality a similar functionality is required for a rather big and complex model. To change this behaviour with the generated names is not possible since it is a requirement.)
import textx
MyLanguage = """
Model
: (locations+=Location)*
(employees+=Employee)*
(positions+=Position)*
(projects+=Project)*
;
Project
: 'project' name=ID
('{'
('use' use=[Position])*
'}')?
;
Position
: 'define' 'position' employee=[Employee|FQN] '->' location=[Location|FQN] ('as' name=ID)?
;
Employee
: 'employee' name=ID
;
Location
: 'location' name=ID
( '{'
(sub_location+=Location)+
'}')?
;
FQN
: ID('.' ID)*
;
Comment:
/\/\/.*$/
;
"""
MyCode = """
location Building
{
location Entrance
location Exit
}
employee Hans
employee Juergen
// Shall be referred to with the given name: "EntranceGuy"
define position Hans->Building.Entrance as EntranceGuy
// Shall be referred to with the autogenerated name: <Employee>"At"<LastLocation>
define position Juergen->Building.Exit
project SecurityProject
{
use EntranceGuy
use JuergenAtExit
}
"""
def position_name_generator(obj):
if "" == obj.name:
obj.name = obj.employee.name + "At" + obj.location.name
def main():
meta_model = textx.metamodel_from_str(MyLanguage)
meta_model.register_scope_providers({
"Position.location": textx.scoping.providers.FQN(),
})
meta_model.register_obj_processors({
"Position": position_name_generator,
})
model = meta_model.model_from_str(MyCode)
assert model, "Could not create model..."
if "__main__" == __name__:
main()
What is the textx way to solve this...
The use case you describe is to define the name of an object based on other model elements, including a reference to other model elements. This is currently not part of any test and use cases included in our test suite and the textx docu.
Object processors are executed at defined stages during model construction (see http://textx.github.io/textX/stable/scoping/#using-the-scope-provider-to-modify-a-model). In the described setup they are executed after reference resolution. Since the name to be defined/deduced itself is required for reference resolution, object processors cannot be used here (even if we allow to control when object processors are executed, before or after scope resolution, the described setup still will not work).
Given the dynamics of model loading (see http://textx.github.io/textX/stable/scoping/#using-the-scope-provider-to-modify-a-model), the solution is located within a scope provider (as you suggested). Here, we allow to control the order of reference resolution, such that references to the object being named by a custom procedure are postponed, until references required to deduce/define the name resolved.
Possible workaround
A preliminary sketch of how your use case can be solved is discussed in a https://github.com/textX/textX/pull/194 (with an attached issue https://github.com/textX/textX/issues/193). This textx PR contains a version of scoping.py you could probably use for your project (just copy and rename the module). A full-fledged solution could be part of the textx TEP-001, where we plan to make scoping more controllable to the end-user.
Playing around with this absolutely interesting issue revealed new aspects to me for the textx framework.
names dependent on model contents (involving unresolved references). This name resolution, which can be Postponed (in the referenced PR, see below), in terms of our reference resolution logic.
Even more interesting are the consequences of that: What happens to references pointing to locations, where unresolved names are found? Here, we must postpone the reference resolution process, because we cannot know if the name might match when resolved...
Your example is included: https://github.com/textX/textX/blob/analysis/issue193/tests/functional/test_scoping/test_name_resolver/test_issue193_auto_name.py

How to add w:altChunk and its relationship with python-docx

I have a use case that make use of <w:altChunk/> element in Word document by inject (fragment of) HTML file as alternate chunks and let Word do it works when the file gets opened. The current implementation was using XML/XSL to compose WordML XML, modify relationships, and do all packaging stuffs manually which is a real pain.
I wanted to move to python-docx but the API doesn't support this directly. Currently I found a way to add the <w:altChunk/> in the document XML. But still struggle to find a way to add relationship and related file to the package.
I think I should make a compatible part and pass it to document.part.relate_to function to do its job. But still can't figure how to:
from docx import Document
from docx.oxml import OxmlElement, qn
from docx.opc.constants import RELATIONSHIP_TYPE as RT
def add_alt_chunk(doc: Document, chunk_part):
''' TODO: figuring how to add files and relationships'''
r_id = doc.part.relate_to(chunk_part, RT.A_F_CHUNK)
alt = OxmlElement('w:altChunk')
alt.set(qn('r:id'), r_id)
doc.element.body.sectPr.addprevious(alt)
Update:
As per scanny's advice, below is my working code. Thank you very much Steve!
from docx import Document
from docx.oxml import OxmlElement
from docx.oxml.ns import qn
from docx.opc.part import Part
from docx.opc.constants import RELATIONSHIP_TYPE as RT
def add_alt_chunk(doc: Document, html: str):
package = doc.part.package
partname = package.next_partname('/word/altChunk%d.html')
alt_part = Part(partname, 'text/html', html.encode(), package)
r_id = doc.part.relate_to(alt_part, RT.A_F_CHUNK)
alt_chunk = OxmlElement('w:altChunk')
alt_chunk.set(qn('r:id'), r_id)
doc.element.body.sectPr.addprevious(alt_chunk)
doc = Document()
doc.add_paragraph('Hello')
add_alt_chunk(doc, "<body><strong>I'm an altChunk</strong></body>")
doc.add_paragraph('Have a nice day!')
doc.save('test.docx')
Note: the altChunk parts only work/appear when document is open using MS Word
Well, some hints here anyway. Maybe you can post your working code at the end as a full "answer":
The alt-chunk part needs to start its life as a docx.opc.part.Part object.
The blob argument should be the bytes of the file, which is often but not always plain text. It must be bytes though, not unicode (characters), so any encoding has to happen before calling Part().
I expect you can work out the other arguments:
package is the overall OPC package, available on document.part.package.
You can use docx.opc.package.OpcPackage.next_partname() to get an available partname based on a root template like: "altChunk%s" for a name like "altChunk3". Check what partname prefix Word uses for these, possibly with unzip -l has-an-alt-chunk.docx; should be easy to spot.
The content-type is one in docx.opc.constants.CONTENT_TYPE. Check the [Content_Types].xml part in a .docx file that has an altChunk to see what they use.
Once formed, the document_part.relate_to() method will create the proper relationship. If there is more than one relationship (not common) then you need to create each one separately. There would only be one relationship from a particular part, just some parts are related to more than one other part. Check the relationships in an existing .docx to see, but pretty good guess it's only the one in this case.
So your code would look something like:
package = document.part.package
partname = package.next_partname("altChunkySomethingPrefix")
content_type = docx.opc.constants.CONTENT_TYPE.THE_RIGHT_MIME_TYPE
blob = make_the_altChunk_file_bytes()
alt_chunk_part = Part(partname, content_type, blob, package)
rId = document.part.relate_to(alt_chunk_part, RT.A_F_CHUNK)
etc.

where is the word/_rels/document.xml.rels in python docx object?

I need the content of word/_rels/document.xml.rels to get the image infomation. Does python-docx store it?
I use this:
>>> from docx import Document as d
>>> x=d('a.docx')
there seems no way to get it in x object.
python-docx and python-pptx share a common opc subpackage; this is the docx.opc subpackage.
This layer abstracts the details of the .rels files, among other things.
You can get to it using:
>>> document = Document()
>>> document_part = document.part
>>> rels = document_part.rels
>>> for r in rels:
... print r.rId
'rId2'
'rId1'
'rId3'
How you use it most effectively depends on what you're trying to get at. Usually one just wants to get a related part and doesn't care about navigating the details of the packaging. For that there are these higher level methods:
docx.opc.part.Part.part_related_by()
docx.opc.part.Part.related_parts[rId]
In general the route from the object at hand is:
to the part it's contained in (often available on obj.part)
to the related part by use of .part_related_by() (using relationship type) or .related_parts[rId] (it's a dict).
back down the the API object via X_Part.main_obj e.g. DocumentPart.document
The areas in the code you might be interested in looking closer at are:
docx/parts/
docx/opc/part.py

Find Table object in query

Using sqlalchemy 0.7.2
Is there a way to find the table class from the query object? For example:
q = session.query(Customers)
how can I find Customers in q? Possible? Not Possible?
Yes. You need column_descriptions.
It's a long road to the table, though. sqlalchemy.orm.Query.column_descriptions returns a list of dicts, describing each query entity as it was given to query. in your example, there's only one entity, so you need the first item from that list. And since you're interested in the type of the query entity, rather than its' structure, you want the "type" key from that list:
q_entity = q.column_descriptions[0]['type']
assert q_entity == Customer
Accessing the table for the mapped class requires snooping around in the mapper subsystem. for that, you should use manager_of_class. The table is accessible from the manager through the mapper.mapped_table attribute:
from sqlalchemy.orm.attribute import manager_of_class
q_table = manager_of_class(q_entity).mapper.mapped_table
Resist the urge to skip strait to the mapper through Customer.__mapper__, or even Customer.__table__; That's specific to sqlalchemy.ext.declarative, and won't work with classes that are mapped by other means.