Re: [sqlalchemy] helper function to get and/or update the InstrumentedList from a relationship on a model

[Mike Bayer]

getattr() is the most direct way but you can also use 
mapper.all_orm_descriptors[property_name] 

On Wed, Aug 12, 2020, at 11:49 AM, Mark Aquino wrote:
> I was interested in creating a generic helper function to get the 
> instrumented list associated with a "RelationshipProperty" for a Model,
> you can get the relationship from 
> inspect(model).mapper.relationships.items(), but the relationship is just the 
> RelationshipProperty object and *not* the InstrumentedList.  I could not see 
> a way to get the instrumented list from the relationship and was wondering if 
> I was missing something or if we really must use getattr(model, 
> property_name) to get the InstrumentedList.
> 
> I also noticed that I couldn't directly set the instrumented list values from 
> the relationship; I can do add/remove/extend operations on the list but not 
> e.g. `relationship = [item1, item2, item3,]`, for that I had to use 
> setattr(model, relationship_name, values_array)
> 
> Any feedback on my approach or if there is a better way to do this would be 
> appreciated!
> 
> def type_query(type, id):
> type_query = g.session.query(type).filter_by(id=id).one()
> return type_query
> 
> def get_relationship_from_model(parent_entity, relationship_model):
> relationship_label = None
> for label, r in inspect(parent_entity).mapper.relationships.items():
> if r.entity.class_ == relationship_model:
> relationship_label = label
> break
> relationship = getattr(parent_entity, relationship_label)
> return relationship_label, relationship
> 
> 
> def update_list(relationship_model, entity_model, operation: str, id_list: 
> Optional[List[UUID]] = None):
> """
> id list = ids to add or remove from relationship
> relationship_type = the `type` of the relationship on entity model, e.g...
> entity_model = the model whose relationships are being updated
> operation = add or remove
> :param id_list:
> :param relationship_model:
> :param entity_model:
> :param operation:
> :return:
> """
> if not id_list:
> return entity_model
> # e.g. CvMeasurementAttribute -> cv_measurement_attributes
> relationship_label, relationship = 
> get_relationship_from_model(parent_entity=entity_model,
>
> relationship_model=relationship_model)
> entities_to_relate = [
> type_query(type=relationship_model, id=id_) for id_ in id_list
> ]
> if operation == "add":
> relationship.extend(entities_to_relate)
> elif operation == "remove":
> for entity in entities_to_relate:
> relationship.remove(entity)
> else:
> setattr(entity_model, relationship_label, entities_to_relate)
> return entity_model
> 
> 
> 

> --
> SQLAlchemy - 
> The Python SQL Toolkit and Object Relational Mapper
>  
> http://www.sqlalchemy.org/
>  
> To post example code, please provide an MCVE: Minimal, Complete, and 
> Verifiable Example. See http://stackoverflow.com/help/mcve for a full 
> description.
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>  
> .

-- 
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The Python SQL Toolkit and Object Relational Mapper

http://www.sqlalchemy.org/

To post example code, please provide an MCVE: Minimal, Complete, and Verifiable 
Example.  See  http://stackoverflow.com/help/mcve for a full description.
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[sqlalchemy] helper function to get and/or update the InstrumentedList from a relationship on a model

[Mark Aquino]

I was interested in creating a generic helper function to get the 
instrumented list associated with a "RelationshipProperty" for a Model,
you can get the relationship from 
inspect(model).mapper.relationships.items(), but the relationship is just 
the RelationshipProperty object and *not* the InstrumentedList.  I could 
not see a way to get the instrumented list from the relationship and was 
wondering if I was missing something or if we really must use 
getattr(model, property_name) to get the InstrumentedList.

I also noticed that I couldn't directly set the instrumented list values 
from the relationship; I can do add/remove/extend operations on the list 
but not e.g. `relationship = [item1, item2, item3,]`, for that I had to use 
setattr(model, relationship_name, values_array)

Any feedback on my approach or if there is a better way to do this would be 
appreciated!

def type_query(type, id):
type_query = g.session.query(type).filter_by(id=id).one()
return type_query

def get_relationship_from_model(parent_entity, relationship_model):
relationship_label = None
for label, r in inspect(parent_entity).mapper.relationships.items():
if r.entity.class_ == relationship_model:
relationship_label = label
break
relationship = getattr(parent_entity, relationship_label)
return relationship_label, relationship


def update_list(relationship_model, entity_model, operation: str, id_list: 
Optional[List[UUID]] = None):
"""
id list = ids to add or remove from relationship
relationship_type = the `type` of the relationship on entity model, e.g...
entity_model = the model whose relationships are being updated
operation = add or remove
:param id_list:
:param relationship_model:
:param entity_model:
:param operation:
:return:
"""
if not id_list:
return entity_model
# e.g. CvMeasurementAttribute -> cv_measurement_attributes
relationship_label, relationship = 
get_relationship_from_model(parent_entity=entity_model,
   
relationship_model=relationship_model)
entities_to_relate = [
type_query(type=relationship_model, id=id_) for id_ in id_list
]
if operation == "add":
relationship.extend(entities_to_relate)
elif operation == "remove":
for entity in entities_to_relate:
relationship.remove(entity)
else:
setattr(entity_model, relationship_label, entities_to_relate)
return entity_model



-- 
SQLAlchemy - 
The Python SQL Toolkit and Object Relational Mapper

http://www.sqlalchemy.org/

To post example code, please provide an MCVE: Minimal, Complete, and Verifiable 
Example.  See  http://stackoverflow.com/help/mcve for a full description.
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