Re: [sqlalchemy] returning a dynamic query from Column.default callable

[Jonathan Beluch]

We're just using core, is there some equivalent?

On Thursday, March 17, 2016 at 3:19:23 PM UTC-6, Mike Bayer wrote:
>
>
>
> On 03/17/2016 04:47 PM, Jonathan Beluch wrote: 
> > Background: Using core we have tables defined in a few separate files. 
> > Goal: To have column defaults be selectables which reference other 
> > tables while avoiding circular imports. To avoid circular imports I 
> > cannot always build the selects at import time, they have to be 
> > generated inside a function that takes table/col names similar to how 
> > FKs work. 
> > 
> > It seems that a callable for Column.default cannot return an uncompiled 
> > statement. Two solutions I see: 
> > 
> > 1) Use the context provided to default callables to compile the dynamic 
> > select statement. 
> > 2) Implement something similar to FKs, using all the parent attach 
> > events to set .arg to a selectable on a subclass of ColumnDefault. 
> > 
> > Thoughts? 
>
> A column default callable is expected to produce the value that's to be 
> embedded into the INSERT values.   You can execute any SQL you'd like 
> there, but that's after the INSERT statement's string form is already 
> decided. 
>
> If the goal is that the default is a SQL clause to be embedded in the 
> string form of the INSERT, then you use a fixed default that is 
> represented by that SQL clause. 
>
> If you can't generate that SQL clause due to imports, there's various 
> ways to defer the production of the Column but the simplest way, not 
> necessarily the nicest, is to stick it in declare_first: 
>
> from sqlalchemy import * 
> from sqlalchemy.orm import * 
> from sqlalchemy.ext.declarative import declarative_base 
>
> Base = declarative_base() 
>
>
> class B(Base): 
>  __tablename__ = 'b' 
>  id = Column(Integer, primary_key=True) 
>
>  @classmethod 
>  def __declare_first__(cls): 
>  cls.b = Column(Integer, default=select([A]).as_scalar()) 
>
>
> class A(Base): 
>  __tablename__ = 'a' 
>  id = Column(Integer, primary_key=True) 
>
> e = create_engine("sqlite://", echo=True) 
> configure_mappers() 
> Base.metadata.create_all(e) 
>
> s = Session(e) 
> s.add(B()) 
> s.commit() 
>
>
> __declare_first__ is actually just a hook for the before_configured 
> event so that's actually using the events in any case. 
>
>
>
>
> > 
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[sqlalchemy] Number of Open ConnectionPool connections

[Dave Ekhaus]

Hi All

Is there a way to determine the exact number of open db connections in 
SQLAlchemy's connection pool ?

Thanks
Dave

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Re: [sqlalchemy] how can I search rows containing jsonb data on the basis of it's key>

[Jonathan Vanasco]

To add to Simon's resposne: SqlAlchemy has some postgres specific 
extensions to the dialect.

http://docs.sqlalchemy.org/en/latest/dialects/postgresql.html#sqlalchemy.dialects.postgresql.JSONB

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Re: [sqlalchemy] Modeling single FK to multiple tables

[Mike Bayer]

On 03/17/2016 03:11 PM, Alex Hall wrote:

Hello all,
It seems like I can't go a day without running into some kind of wall.
This one is a conceptual one regarding foreign keys. I have to somehow
get the same FK column in table A pointing to IDs in tables B and C.


So a real foreign key constraint is not capable of this.  Repurposing a 
single column to occasionally point to one table or another is a famous 
anti-pattern I've spoke of much (warning, this is *extremely* old, but 
the general idea still holds):


http://techspot.zzzeek.org/2007/05/29/polymorphic-associations-with-sqlalchemy/


I have an updated version of all the various "polymoprhic association" 
examples in SQLAlchemy itself at 
http://docs.sqlalchemy.org/en/rel_1_0/orm/examples.html#module-examples.generic_associations. 
 This includes the "single column pointing to multiple tables" hack, as 
well as three other versions of the same business object geometry which 
preserve relational integrity within the schema design.




At one person's suggestion, I'm making classes for my tables, even
though I'm using automap. This is to let me stop doing a ton of joins,
making querying much easier... I hope! I'm defining all the foreign
keys between my tables manually. For instance:

class item(base):
  __tablename__ = "item"
  itm_id = Column(Integer, primary_key=True)
  vendornum = Column(String, ForeignKey(VENDR.PVVNNO))

class vendorTable(base):
  __tablename__ = "VENDR"
  PVVNNO = Column(String, primary_key=True)

If I've understood correctly, I'll now be able to say
item.vendornum.vendor_full_name
to get the vendor's full name for any item.

Here's the problem. Items have attachments, and attached text,
respectively held in attach and attach_text tables. Binding them to
items is a table called assignment. Assignment is pretty
straightforward, with an itm_id and an attachment id (att_id). The
trouble is that this att_id occurs in both attach and attach_text. I
can make att_id a foreign key to one table or the other, but I'm not
sure how to make it go to both tables.


the "generic_fk" example illustrates a pattern for working with this.

Getting this all to work with automap is another layer of complexity, 
you certainly want all of this part of it laid out before you reflect 
the rest of the database columns.





class assignmentTable(base):
  __tablename__ = "assignment"
  itm_id = Column(Integer, ForeignKey(item.itm_id))
  #the following column has to point to attach_text.att_id AS WELL
   att_id = Column(Integer, ForeignKey(attachment.att_id))
  seq_num = Column(Integer)
  asn_primary = Column(Integer, nullable=True)

class attachmentTable(base):
  __tablename__ = "attachment"
  att_id = Column(Integer, primary_key=True)

class attachmentTextTable(base):
  __tablename__ = "attach_text"
  att_id = Column(Integer, primary_key=True)



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[sqlalchemy] How make update in Association Objects

[Mário Idival]

Hi,

I have a problema to make updates on tables with Association Objects


class Type(PrimaryKey, Base):
__tablename__ = "types"

name = Column(Unicode, nullable=False)
description = Column(Unicode)

users = relationship(User, secondary="type_users")

class TypeUser(Base):
__tablename__ = "type_users"

type_id = Column(Integer, ForeignKey("types.pk"), primary_key=True)
user_id = Column(Integer, ForeignKey("users.pk"), primary_key=True)

type = relationship(Type, backref=backref("type_users", lazy="dynamic"))
user = relationship(User, backref=backref("type", uselist=False))

class User(PrimaryKey, Base):
__tablename__ = "users"
# some irrelevant datas.

To save is easy...

user = User.query.get(pk)
type = Type.query.get(other_pk)

type.users.append(user)



How I can update o `type` of user??

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Re: [sqlalchemy] Re: Database synchronisation

[Mike Bayer]

these are all documented functions and I didn't check the exact API.

Here is a full example:

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()


class A(Base):
__tablename__ = 'a'
id = Column(Integer, primary_key=True)
a = Column(Integer)
b = Column(Integer)

e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)

session = Session(e)

session.add(A(a=1, b=2))
session.commit()

a1 = session.query(A).first()

mapper = inspect(a1).mapper

session.expire(a1, [col.key for col in mapper.primary_key])
make_transient(a1)

session.add(a1)
session.commit()



On 03/18/2016 03:54 AM, milan53064...@gmail.com wrote:

Hi Mike,
thanks for idea.
I am getting this exception :
session.expire(test_run, [col.key for col in mapper.primary_keys])
AttributeError: 'InstanceState' object has no attribute 'primary_keys'

Do I need setup something on the schema objects in order to get this
primary_keys?

right now I have this parameters on every relation in the objects in the
schema  :

lazy='joined',cascade="save-update, merge, delete, expunge")



Dňa štvrtok, 17. marca 2016 16:56:05 UTC+1 Mike Bayer napísal(-a):


how about:


from sqlalchemy import inspect

mapper = inspect(obj)

session.expire(obj, [col.key for col in mapper.primary_keys])
make_transient(obj)



On 03/17/2016 10:54 AM, milan5...@gmail.com  wrote:
 > Right now I am taking  test run object from local database,
then I
 > call expunge on that object (cascade is set to expunge).
 >
 >   then I put this object into this python method :
 >
 > def _reset_primary_keys(self, test_run):
 > make_transient(test_run)
 > test_run.ID= None
 >  if test_run.OrderNumber:
 > make_transient(test_run.OrderNumber)
 > test_run.OrderNumber.ID = None
 >
 >  for equipmentin test_run.TestEquipments:
 > make_transient(equipment)
 > equipment.ID= None
 >
 >  for trdin test_run.TestRunToDevs:
 > make_transient(trd)
 > trd.ID= None
 >
 >  if trd.TestedDut:
 > make_transient(trd.TestedDut)
 > trd.TestedDut.ID = None
 >
 >  for test_stepin trd.TestSteps:
 > make_transient(test_step)
 > test_step.ID= None
 >
 >  for test_resultin test_step.TestResults:
 > make_transient(test_result)
 > test_result.ID= None
 >
 >
 > This method reset all primary keys, so I can merge it into master
 > database which will generate new primary keys. Is there a better or
 > easier way how to do it?
 >
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[sqlalchemy] Modeling single FK to multiple tables

[Alex Hall]

Hello all,
It seems like I can't go a day without running into some kind of wall.
This one is a conceptual one regarding foreign keys. I have to somehow
get the same FK column in table A pointing to IDs in tables B and C.

At one person's suggestion, I'm making classes for my tables, even
though I'm using automap. This is to let me stop doing a ton of joins,
making querying much easier... I hope! I'm defining all the foreign
keys between my tables manually. For instance:

class item(base):
 __tablename__ = "item"
 itm_id = Column(Integer, primary_key=True)
 vendornum = Column(String, ForeignKey(VENDR.PVVNNO))

class vendorTable(base):
 __tablename__ = "VENDR"
 PVVNNO = Column(String, primary_key=True)

If I've understood correctly, I'll now be able to say
item.vendornum.vendor_full_name
to get the vendor's full name for any item.

Here's the problem. Items have attachments, and attached text,
respectively held in attach and attach_text tables. Binding them to
items is a table called assignment. Assignment is pretty
straightforward, with an itm_id and an attachment id (att_id). The
trouble is that this att_id occurs in both attach and attach_text. I
can make att_id a foreign key to one table or the other, but I'm not
sure how to make it go to both tables.

class assignmentTable(base):
 __tablename__ = "assignment"
 itm_id = Column(Integer, ForeignKey(item.itm_id))
 #the following column has to point to attach_text.att_id AS WELL
  att_id = Column(Integer, ForeignKey(attachment.att_id))
 seq_num = Column(Integer)
 asn_primary = Column(Integer, nullable=True)

class attachmentTable(base):
 __tablename__ = "attachment"
 att_id = Column(Integer, primary_key=True)

class attachmentTextTable(base):
 __tablename__ = "attach_text"
 att_id = Column(Integer, primary_key=True)

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Re: [sqlalchemy] Re: Database synchronisation

[Mike Bayer]

how about:


from sqlalchemy import inspect

mapper = inspect(obj)

session.expire(obj, [col.key for col in mapper.primary_keys])
make_transient(obj)



On 03/17/2016 10:54 AM, milan53064...@gmail.com wrote:

Right now I am taking  test run object from local database, then I
call expunge on that object (cascade is set to expunge).

  then I put this object into this python method :

def _reset_primary_keys(self, test_run):
make_transient(test_run)
test_run.ID= None
 if test_run.OrderNumber:
make_transient(test_run.OrderNumber)
test_run.OrderNumber.ID= None

 for equipmentin test_run.TestEquipments:
make_transient(equipment)
equipment.ID= None

 for trdin test_run.TestRunToDevs:
make_transient(trd)
trd.ID= None

 if trd.TestedDut:
make_transient(trd.TestedDut)
trd.TestedDut.ID= None

 for test_stepin trd.TestSteps:
make_transient(test_step)
test_step.ID= None

 for test_resultin test_step.TestResults:
make_transient(test_result)
test_result.ID= None


This method reset all primary keys, so I can merge it into master
database which will generate new primary keys. Is there a better or
easier way how to do it?

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[sqlalchemy] Backref primary join condition stopped working in 0.9.4

[Thorsten von Stein]

For several years, I have been using a pattern for making a many-to-one 
relationship from *cls* to *remoteCls* with a one-to-many backref with a 
join condition cls.foreignKey == remoteCls.id, where
*cls* has a deletion flag _del which should exclude *cls* instances with del 
!= 0 from the backref collection.

Since the condition involving _del is only relevant in the one-to-many 
direction, I defined separate primaryjoin conditions which included this 
condition only for the backref.

br = backref(
backref,
collection_class=list,
primaryjoin=and_(remoteCls.id==remote(getattr(cls, foreignKey)), 
cls._del==0))

rel = relationship(
remoteCls,
remote_side=remoteCls.id,
primaryjoin=getattr(cls, foreignKey)==remoteCls.id,
backref=br)

I have used this pattern successfully for years until I recently upgraded 
SqlAlchemy to the latest version and found that the join condition on the 
backref seems to be ignored and queries include instances that are flagged 
as deleted via the _del column. I tested several intermediate SqlAlchemy 
version and found that the first one which breaks the pattern is 0.9.4.

Subsequently I found that removing the primary join condition on the 
backref and including the _del != 0 condition in the forward primary join 
condition seems to restore the intended behavior, but now many queries 
involving large collections are dramatically slowed to make this solution 
unworkable.

I reviewed the desciptions of changes, but they did not clarify for me why 
the pattern above does not work any more. Is there a flaw in my code that I 
am missing?

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Re: [sqlalchemy] how can I search rows containing jsonb data on the basis of it's key>

[Jonathan Vanasco]

On Friday, March 18, 2016 at 8:48:48 AM UTC-4, Simon King wrote:

I think you should be able to use something like:
>

 I find it easier to run raw sql to grab data like that.

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[sqlalchemy] Defining relationships (was: joins instead of filters remove attributes of results)

[Alex Hall]

If I define all the relationships as suggested, I could do
result.itm_id
or
result.attribute_value
and it would all work? Would I still need to specify, in my initial
query, things like
.filter(itemTable.itm_id = attachmentAssignmentTable.itm_id\
.filter(attachmentTable.att_id = attachmentAssignmentTable.att_id)

to get all attachments assigned to a given item? I'll read more about
this and play with it, but I wanted to ask here as well in case
someone sees that the design of this database will cause problems with
relationships.

On 3/16/16, Simon King  wrote:
> On Wed, Mar 16, 2016 at 1:07 PM, Alex Hall  wrote:
>
>> Hello all,
>> I'm running a different query than yesterday. Before, I had something
>> like:
>>
>> items = session.query(itemTable, attachmentTable, attachmentTextTable,
>> assignmentTable, attributeTable, attributeValueTable,
>> attributeValueAssignmentTable, vendorTable)\
>> .filter(attachmentTable.itm_id == itemTable.itm_id)\
>> #and so on, a bunch of .filter calls
>>
>> Then, in the loop iterating over the results, I could do this:
>>
>> for result in queryResults:
>>  itemID = result.item.itm_id
>>
>
> Because you wrote "session.query(itemTable, attachmentTable,
> attachmentTextTable)", the results that you get back from the query are
> like a tuple with 3 items corresponding to the 3 tables that you queries.
> result[0] would be the data from itemTable, result[1] is from
> attachmentTable, and result[2] is from attachmentTextTable. It also
> supports name-based access, which is why you were able to refer to
> "result.item" and "result.attach_text".
>
>
>>
>> Now that I'm using a bunch of outer left joins, that code is suddenly
>> not working. I get an error when I say
>> result.item.itm_id
>> AttributeError: 'item' object has no attribute 'item'
>>
>> The problem is that my query starts out with only one table passed to
>> session.query(), not all of them. Thus my result is of type 'item',
>> which is the table passed in. That would be okay, except that I need
>> to access values of other tables in the result, so even if I change
>> id = result.item.itm_id
>> to
>> id = result.itm_id
>> When I then say
>> description = result.attach_text.att_value
>> AttributeError: 'item' object has no attribute 'attach_text'
>>
>>
> First, it helps to be precise about your terminology. SQLAlchemy
> distinguishes between the object representing a table, and a class that you
> are mapping to that table. You've talked about using automapper in the
> past, so I assume you are passing a mapped class, not a table, to
> session.query().
>
> When you pass a single mapped class, the results you get back are instances
> of that class.
>
>
>
>> I know why it doesn't. What I don't know is how to get my query
>> results to hold all the information from all the tables, or how to
>> access it if they do already, but in a different way than before. My
>> new query is this:
>>
>> items = session.query(itemTable)\
>> .outerjoin(vendorTable, vendorTable.PVVNNO == itemTable.itm_vendornum)\
>> .outerjoin(assignmentTable, assignmentTable.itm_id == itemTable.itm_id)\
>> .filter(assignmentTable.att_id == attachmentTable.att_id)\
>> .outerjoin(attachmentTextTable, assignmentTable.att_id ==
>> attachmentTextTable.att_id)\
>> .outerjoin(attributeValueAssignmentTable,
>> attributeValueAssignmentTable.itm_id == itemTable.itm_id)\
>> .outerjoin(attributeTable, attributeTable.attr_id ==
>> attributeValueAssignmentTable.attr_id)\
>> .filter(attributeValueTable.attr_value_id ==
>> attributeValueAssignmentTable.attr_value_id)\
>> .yield_per(1000)
>>
>> I've also tried the same query, but with the first line changed to:
>> items = session.query(itemTable, attachmentTable, attachmentTextTable,
>> assignmentTable, attributeTable, attributeValueTable,
>> attributeValueAssignmentTable, vendorTable)\
>>
>> The problem here is that, while result.item.* works as expected, other
>> tables don't. For instance, result.attach_text.att_value yields an
>> AttributeError, 'None' type object has no attribute att_value.
>> Clearly, the other tables are in the result, but they're all None. I
>> expected something like that, and only added them back in to see if it
>> might help, but since I call query().outerjoin() I didn't think it
>> would work.
>>
>> I should note that I renamed most of the tables by assigning variables
>> to base.classes.tableName, which is why I'm using "itemTable" here,
>> but in getting attributes of results I use just "item". The 'item'
>> table is called 'item', but I assigned it to a variable called
>> 'itemTable', just for clarity in the script.
>>
>> Is there a way to access the values of a query like this? At the very
>> least, is there a way I can print out all the objects the result
>> object has, so I can work out what to do? Thanks for any help!
>>
>>
> Normally you would do this by setting up relationships between your mapped
> classes, so that when you access "item.attach_text", SQLAlchemy will go and
> fetch the rela

Re: [sqlalchemy] OperationalError with SQLite with simple update query

[Simon King]

On Wed, Mar 16, 2016 at 1:43 PM, Piotr Dobrogost <
p...@2016.groups.google.dobrogost.net> wrote:

> Hi!
>
> When executing below code
>
> DBSession.query(TextValue).\
> filter(Node.id.in_(ids)).\
> update({TextValue.value: appstruct['text_value']},
>  synchronize_session=False)
>
> I get this error:
> OperationalError: (sqlite3.OperationalError) near "FROM": syntax error
> [SQL: u'UPDATE text_values SET value=? FROM nodes WHERE nodes.id IN (?,
> ?, ?, ?)'] [parameters: (u'zzz', u'1685', u'175', u'1688', u'180')]
>
> Does SA construct query which is not valid in SQLite?
> How can I solve this problem?
>
> Regards,
> Piotr Dobrogost
>
>
I'm not sure if sqlite supports multi-table updates. Do you know what sort
of SQL you are expecting to generate here?

(Note that your query appears at least to be missing a join condition
between the TextValue and Node classes)

Simon

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Re: [sqlalchemy] Re: Can I make bulk update through association proxy?

[Piotr Dobrogost]

On Saturday, February 27, 2016 at 10:26:53 PM UTC+1, Mike Bayer wrote:
>
>
> If I can just wrap this up, do i understand correctly that this would 
> the functionality of "joined eager loading", except applied to something 
> like an UPDATE..FROM ? 
>

I think so although I can't say I'm 100% sure as I'm not fluent in neither 
SA nor in SQL.

Jonathan Vanasco wrote earlier: 
>For this general task, I `flush` the session, use the `update` command on 
the target class -- filtering the >WHERE based on the parent object and 
 join conditions --  then I `expire_all` (because that update may have 
>affected in-memory object relations).  There is a small hit on reloading 
all the data, but I've found the `update` >to run considerably faster and 
make it worth-it.

This explains how to do this starting from the "opposite end". I mean the 
situation is that there's some parent_class <-relationship-> target_class 
and I want to update objects of target_class having initially objects of 
parent_class without explicitly selecting objects of target_class first as 
in Jonathan's solution.

Regards,
Piotr

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