Re: Migration fails when changing to single table inheritance

[Michael]

Yes, I'll try Plan A first(do the INSERT FROM first) 

But mainly out of academic curiosity, if I were to start with a blank slate 
as you say, I'd still need to import the existing data that is currently in 
the non-inheritance table schema? So I guess I would just drop the 
database, upgrade to head. At this point I have the latest 
inheritance-based schema but no data. Say I dumped the db to a file before 
I dropped it, does alembic have facilities to take a dumped db and insert 
it into a new/slightly different schema?

On Wednesday, June 7, 2017 at 7:12:27 PM UTC-4, mike bayer wrote:
>
>
>
> On 06/07/2017 07:01 PM, Michael wrote: 
> > Thanks for the insight Mike. I guess the best way to go about that would 
> > be to just call the raw insert sql statemen in the migration? like in 
> > 
> https://stackoverflow.com/questions/23206562/sqlalchemy-executing-raw-sql-with-parameter-bindings/23206636#23206636
>  
>
> i'd start with that just to make sure it gets it working.From there, 
> we do support insert().from_select(select()) if you have the inclination 
> to build a Core SQL statement out of it but if you are only targeting 
> Postgresql it's not critical. 
>
>
> http://docs.sqlalchemy.org/en/latest/core/dml.html?highlight=insert%20from_select#sqlalchemy.sql.expression.Insert.from_select
>  
>
> > Since this app is not in production yet, would it be easier to make the 
> > current schema the initial schema and just insert the data that is in 
> > the MediaChapter table into the new schema just once? I guess could use 
> > bulk_insert() to do that? 
>
> if the data is not there yet, sure it's easier to start with a blank 
> slate if that's what you mean 
>
> > 
> > On Wednesday, June 7, 2017 at 6:14:39 PM UTC-4, mike bayer wrote: 
> > 
> > 
> > 
> > On 06/07/2017 04:44 PM, Michael wrote: 
> >  > Hi all, I have a class called MediaChapter(Base), which I've 
> > refactored 
> >  > into MediaBase(Base) and MediaChapter(MediaBase) When I run the 
> >  > migration, I see: 
> >  > 
> >  > | 
> >  > psycopg2.IntegrityError:insert orupdate on table 
> > "mediachapter"violates 
> >  > foreign key constraint "fk_mediachapter_id_mediabase" 
> >  > DETAIL:Key(id)=(570)isnotpresent intable "mediabase". 
> > 
> > 
> > here's the real error with the SQL: 
> > 
> > sqlalchemy.exc.IntegrityError: (psycopg2.IntegrityError) insert or 
> > update on table "mediachapter" violates foreign key constraint 
> > "fk_mediachapter_id_mediabase" 
> > DETAIL:  Key (id)=(570) is not present in table "mediabase". 
> >[SQL: 'ALTER TABLE mediachapter ADD CONSTRAINT 
> > fk_mediachapter_id_mediabase FOREIGN KEY(id) REFERENCES mediabase 
> > (id)'] 
> > 
> > the error means that your "mediachapter" table contains an id, 
> "570", 
> > which is not present in the "mediabase" table. 
> > 
> > it looks like you are starting with a populated "mediachapter" table 
> > then adding a new table "mediabase".  Before you create the 
> constraint, 
> > you need to run an INSERT on "mediabase" that selects from 
> > "mediachapter", like: 
> > 
> > INSERT INTO mediabase (id, col1, col2, ...) SELECT id, col1, col2, 
> .. 
> > FROM mediachapter 
> > 
> > 
> > 
>

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Re: [sqlalchemy] How to format class property as another accessible property

[Greg Silverman]

Oh right, I've used the @property decorator before, just been a while.

Thanks for the explanation of @hybrid_property. Makes sense.

On Wed, Jun 7, 2017 at 5:32 PM, mike bayer  wrote:

>
>
> On 06/07/2017 06:19 PM, Greg Silverman wrote:
>
>> Thanks, it worked!
>>
>> I tried something similar using the @hybrid_property decorator, but could
>> not get it to work. What exactly is the difference between that and the
>> @property decorator?
>>
>
>
> @property is super normal Python stuff that's in all the Python tutorials
> and is something everyone should use all the time.
>
> @hybrid_property is more of a magic trick that's specific to the kind of
> query interface that SQLAlchemy has - in that in an ORM like SQLAlchemy
> (and lots of others), you access attributes off of classes, as well as
> instances of those classes, as part of regular use of the API.  This is not
> a standard object-oriented thing, it's kind of odd.   The @hybrid_property
> allows you to build functions that act a lot like @property, but they
> accommodate for accessing an attribute both at the "instance" (e.g. 'self')
> level and at the "class" level.   Which translated to SQLAlchemy means, at
> the "row I've loaded into memory" level and the "SQL expression I want to
> execute on the database" level.  The kinds of functions we can use in these
> two very different contexts are quite different.
>
>
>
>
>
>
>
>> Greg--
>>
>>
>> On Wed, Jun 7, 2017 at 5:08 PM, mike bayer > > wrote:
>>
>>
>>
>> On 06/07/2017 02:31 PM, GMS wrote:
>>
>> I am sure this is easier than I am making it, but I just want to
>> add a property to a class so that decimal representations get
>> truncated at 3 decimal digits.
>>
>> My class is this:
>>
>> class Measures(Model):
>> __tablename__= 'xcelera_measures'
>> id= Column(Numeric,primary_key=True)
>>   studyidk= Column(Numeric, ForeignKey('xcel.studyidk'))
>>  xceleragroup= relationship("Xcelera")
>>   explainstring= Column(String(255))
>>   mrn= Column(String(255))
>>   value= Column(Numeric)
>>
>>   __mapper_args__= {
>>   "order_by": [mrn]
>>   }
>>
>>
>> and 'value' is the property/attribute that I want to also have a
>> truncated version available in the class.
>>
>> I tried adding this to the class value_new =
>> column_property("%.3f" % value())
>>
>> but got an error that
>>
>> value_new = column_property("%.3f" % value)
>>
>>
>> "%" is a Python function, that doesn't execute on the database.
>>  This works as a normal Python descriptor:
>>
>> class MyClass(Base):
>>  # ...
>>
>>  @property
>>  def value_new(self):
>>  return "%.3f" % self.value
>>
>>
>>
>>
>>
>>
>>
>>
>> TypeError: float argument required, not Column
>>
>> I also tried this as a hybrid_property, but I don't think I was
>> using it correctly.
>>
>> All I want to do is have the truncated version of my attribute
>> available in my class.
>>
>> Thanks!
>>
>> Greg--
>>
>>
>> -- 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.
>> ---
>> You received this message because you are subscribed to the
>> Google Groups "sqlalchemy" group.
>> To unsubscribe from this group and stop receiving emails from
>> it, send an email to sqlalchemy+unsubscr...@googlegroups.com
>> 
>> > >.
>> To post to this group, send email to sqlalchemy@googlegroups.com
>> 
>> > >.
>> Visit this group at https://groups.google.com/group/sqlalchemy
>> .
>> For more options, visit https://groups.google.com/d/optout
>> .
>>
>>
>> -- 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.
>> --- You received this message because you are subscribed to a topic
>> 

Re: Migration fails when changing to single table inheritance

[Michael]

Thanks for the insight Mike. I guess the best way to go about that would be 
to just call the raw insert sql statemen in the migration? like in 
https://stackoverflow.com/questions/23206562/sqlalchemy-executing-raw-sql-with-parameter-bindings/23206636#23206636

Since this app is not in production yet, would it be easier to make the 
current schema the initial schema and just insert the data that is in the 
MediaChapter table into the new schema just once? I guess could use 
bulk_insert() to do that?

On Wednesday, June 7, 2017 at 6:14:39 PM UTC-4, mike bayer wrote:
>
>
>
> On 06/07/2017 04:44 PM, Michael wrote: 
> > Hi all, I have a class called MediaChapter(Base), which I've refactored 
> > into MediaBase(Base) and MediaChapter(MediaBase) When I run the 
> > migration, I see: 
> > 
> > | 
> > psycopg2.IntegrityError:insert orupdate on table "mediachapter"violates 
> > foreign key constraint "fk_mediachapter_id_mediabase" 
> > DETAIL:Key(id)=(570)isnotpresent intable "mediabase". 
>
>
> here's the real error with the SQL: 
>
> sqlalchemy.exc.IntegrityError: (psycopg2.IntegrityError) insert or 
> update on table "mediachapter" violates foreign key constraint 
> "fk_mediachapter_id_mediabase" 
> DETAIL:  Key (id)=(570) is not present in table "mediabase". 
>   [SQL: 'ALTER TABLE mediachapter ADD CONSTRAINT 
> fk_mediachapter_id_mediabase FOREIGN KEY(id) REFERENCES mediabase (id)'] 
>
> the error means that your "mediachapter" table contains an id, "570", 
> which is not present in the "mediabase" table. 
>
> it looks like you are starting with a populated "mediachapter" table 
> then adding a new table "mediabase".  Before you create the constraint, 
> you need to run an INSERT on "mediabase" that selects from 
> "mediachapter", like: 
>
> INSERT INTO mediabase (id, col1, col2, ...) SELECT id, col1, col2, .. 
> FROM mediachapter 
>
>
>
>

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Re: [sqlalchemy] How to format class property as another accessible property

[mike bayer]

On 06/07/2017 06:19 PM, Greg Silverman wrote:

Thanks, it worked!

I tried something similar using the @hybrid_property decorator, but 
could not get it to work. What exactly is the difference between that 
and the @property decorator?



@property is super normal Python stuff that's in all the Python 
tutorials and is something everyone should use all the time.


@hybrid_property is more of a magic trick that's specific to the kind of 
query interface that SQLAlchemy has - in that in an ORM like SQLAlchemy 
(and lots of others), you access attributes off of classes, as well as 
instances of those classes, as part of regular use of the API.  This is 
not a standard object-oriented thing, it's kind of odd.   The 
@hybrid_property allows you to build functions that act a lot like 
@property, but they accommodate for accessing an attribute both at the 
"instance" (e.g. 'self') level and at the "class" level.   Which 
translated to SQLAlchemy means, at the "row I've loaded into memory" 
level and the "SQL expression I want to execute on the database" level. 
 The kinds of functions we can use in these two very different contexts 
are quite different.









Greg--

On Wed, Jun 7, 2017 at 5:08 PM, mike bayer > wrote:




On 06/07/2017 02:31 PM, GMS wrote:

I am sure this is easier than I am making it, but I just want to
add a property to a class so that decimal representations get
truncated at 3 decimal digits.

My class is this:

class Measures(Model):
__tablename__= 'xcelera_measures'
id= Column(Numeric,primary_key=True)
  studyidk= Column(Numeric, ForeignKey('xcel.studyidk'))
 xceleragroup= relationship("Xcelera")
  explainstring= Column(String(255))
  mrn= Column(String(255))
  value= Column(Numeric)

  __mapper_args__= {
  "order_by": [mrn]
  }


and 'value' is the property/attribute that I want to also have a
truncated version available in the class.

I tried adding this to the class value_new =
column_property("%.3f" % value())

but got an error that

value_new = column_property("%.3f" % value)


"%" is a Python function, that doesn't execute on the database. 
This works as a normal Python descriptor:


class MyClass(Base):
 # ...

 @property
 def value_new(self):
 return "%.3f" % self.value








TypeError: float argument required, not Column

I also tried this as a hybrid_property, but I don't think I was
using it correctly.

All I want to do is have the truncated version of my attribute
available in my class.

Thanks!

Greg--


-- 
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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.


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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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Re: [sqlalchemy] How to format class property as another accessible property

[Greg Silverman]

Thanks, it worked!

I tried something similar using the @hybrid_property decorator, but could
not get it to work. What exactly is the difference between that and the
@property decorator?

Greg--

On Wed, Jun 7, 2017 at 5:08 PM, mike bayer  wrote:

>
>
> On 06/07/2017 02:31 PM, GMS wrote:
>
>> I am sure this is easier than I am making it, but I just want to add a
>> property to a class so that decimal representations get truncated at 3
>> decimal digits.
>>
>> My class is this:
>>
>> class Measures(Model):
>> __tablename__= 'xcelera_measures'
>> id= Column(Numeric,primary_key=True)
>>  studyidk= Column(Numeric, ForeignKey('xcel.studyidk'))
>> xceleragroup= relationship("Xcelera")
>>  explainstring= Column(String(255))
>>  mrn= Column(String(255))
>>  value= Column(Numeric)
>>
>>  __mapper_args__= {
>>  "order_by": [mrn]
>>  }
>>
>>
>> and 'value' is the property/attribute that I want to also have a
>> truncated version available in the class.
>>
>> I tried adding this to the class value_new = column_property("%.3f" %
>> value())
>>
>> but got an error that
>>
>> value_new = column_property("%.3f" % value)
>>
>
> "%" is a Python function, that doesn't execute on the database.  This
> works as a normal Python descriptor:
>
> class MyClass(Base):
> # ...
>
> @property
> def value_new(self):
> return "%.3f" % self.value
>
>
>
>
>
>
>
>
>> TypeError: float argument required, not Column
>>
>> I also tried this as a hybrid_property, but I don't think I was using it
>> correctly.
>>
>> All I want to do is have the truncated version of my attribute available
>> in my class.
>>
>> Thanks!
>>
>> Greg--
>>
>>
>> --
>> 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.
>> ---
>> You received this message because you are subscribed to the Google Groups
>> "sqlalchemy" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to sqlalchemy+unsubscr...@googlegroups.com > sqlalchemy+unsubscr...@googlegroups.com>.
>> To post to this group, send email to sqlalchemy@googlegroups.com > sqlalchemy@googlegroups.com>.
>> Visit this group at https://groups.google.com/group/sqlalchemy.
>> For more options, visit https://groups.google.com/d/optout.
>>
>
> --
> 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.
> --- You received this message because you are subscribed to a topic in the
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> pic/sqlalchemy/3FFm1stwEoU/unsubscribe.
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> For more options, visit https://groups.google.com/d/optout.
>



-- 
Greg M. Silverman

 ›  flora-script  ‹
 ›  grenzi.org  ›

-- 
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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Re: Migration fails when changing to single table inheritance

[mike bayer]

On 06/07/2017 04:44 PM, Michael wrote:
Hi all, I have a class called MediaChapter(Base), which I've refactored 
into MediaBase(Base) and MediaChapter(MediaBase) When I run the 
migration, I see:


|
psycopg2.IntegrityError:insert orupdate on table "mediachapter"violates 
foreign key constraint "fk_mediachapter_id_mediabase"

DETAIL:Key(id)=(570)isnotpresent intable "mediabase".



here's the real error with the SQL:

sqlalchemy.exc.IntegrityError: (psycopg2.IntegrityError) insert or 
update on table "mediachapter" violates foreign key constraint 
"fk_mediachapter_id_mediabase"

DETAIL:  Key (id)=(570) is not present in table "mediabase".
 [SQL: 'ALTER TABLE mediachapter ADD CONSTRAINT 
fk_mediachapter_id_mediabase FOREIGN KEY(id) REFERENCES mediabase (id)']


the error means that your "mediachapter" table contains an id, "570", 
which is not present in the "mediabase" table.


it looks like you are starting with a populated "mediachapter" table 
then adding a new table "mediabase".  Before you create the constraint, 
you need to run an INSERT on "mediabase" that selects from 
"mediachapter", like:


INSERT INTO mediabase (id, col1, col2, ...) SELECT id, col1, col2, .. 
FROM mediachapter






|



I'm not sure exactly what this means because I create a mediabase.id.

I did
|
ws-alembic -c kjvrvg/conf/development.ini -x packages=all revision 
--auto-m "MediaBase-MediaChapter subclassing"

|


-- SUCCESS

then
|
ws-alembic -c kjvrvg/conf/development.ini -x packages=all upgrade head
|


-- FAILED


Here are my models, MediaBase:

|
classMediaBase(Base):
#: The table in the database
 __tablename__ ="mediabase"

#: Database primary key for the row (running counter)
 id =Column(Integer,autoincrement=True,primary_key=True)

# table inheritance
 media_type =Column(String(32),nullable=False)

#: Publicly exposed non-guessable
 uuid =Column(UUID(as_uuid=True),default=uuid4)

 localizedname =Column(Unicode(128),default=None)

#: url
 url =Column(Unicode(384),default=None)

# full iso language-locale identifier i.e. zh-Hans-US
 language_id =Column(String(16),default=None)

# name of the person presenting the material
 presenter_name =Column(Unicode(64),default=None)
 source_material =Column(Unicode(128),default=None)

# table inheritance
 __mapper_args__ ={'polymorphic_on':media_type}

def__repr__(self):
"""Shell and debugger presentation."""
return'{} ({}) {} 
<{}>'.format(self.localizedname,self.language_id,str(self.uuid),self.url)


def__str__(self):
"""Python default and admin UI string presentation."""
return'{} ({}) presenter: {} source: {} 
  <{}>'.format(self.localizedname,self.language_id,self.presenter_name,self.source_material,self.url)



|


and MediaChapter:

|
classMediaChapter(MediaBase):

#: The table in the database
 __tablename__ ="mediachapter"

 __mapper_args__ ={'polymorphic_identity':'chapter'}

 id =Column(Integer,ForeignKey('mediabase.id'),primary_key=True)

#: Which chapter this media is part of
 chapter_id =Column(Integer,ForeignKey('chapter.id'))
 chapter =relationship("Chapter",back_populates="mediachapter")
|




and finally here is the auto-generated migration. I put all files in a 
github Gist.


|
https://gist.github.com/mazz/7d63e521316859f4ae852e5cea5d84eb
|



Any suggestions?
Mazz

|

"""MediaBase-MediaChapter subclassing

Revision ID: a00980918d75
Revises: e74ba4203098
Create Date: 2017-06-07 16:10:29.807437

"""

# revision identifiers, used by Alembic.
revision ='a00980918d75'
down_revision ='e74ba4203098'
branch_labels =None
depends_on =None

importdatetime
importwebsauna.system.model.columns
fromsqlalchemy.types importText# Needed from proper creation of JSON 
fields as Alembic inserts astext_type=Text() row


fromalembic importop
importsqlalchemy assa
fromsqlalchemy.dialects importpostgresql

defupgrade():
# ### commands auto generated by Alembic - please adjust! ###
 op.create_table('mediabase',
 sa.Column('id',sa.Integer(),nullable=False),
 sa.Column('media_type',sa.String(length=32),nullable=False),
 sa.Column('uuid',postgresql.UUID(as_uuid=True),nullable=True),
 sa.Column('localizedname',sa.Unicode(length=128),nullable=True),
 sa.Column('url',sa.Unicode(length=384),nullable=True),
 sa.Column('language_id',sa.String(length=16),nullable=True),
 sa.Column('presenter_name',sa.Unicode(length=64),nullable=True),
 sa.Column('source_material',sa.Unicode(length=128),nullable=True),
 sa.PrimaryKeyConstraint('id',name=op.f('pk_mediabase'))
)
 op.alter_column('group','created_at',
existing_type=postgresql.TIMESTAMP(timezone=True),
type_=websauna.system.model.columns.UTCDateTime(),
existing_nullable=True)
 op.alter_column('group','updated_at',
existing_type=postgresql.TIMESTAMP(timezone=True),
type_=websauna.system.model.columns.UTCDateTime(),
existing_nullable=True)
 

Re: [sqlalchemy] How to format class property as another accessible property

[mike bayer]

On 06/07/2017 02:31 PM, GMS wrote:
I am sure this is easier than I am making it, but I just want to add a 
property to a class so that decimal representations get truncated at 3 
decimal digits.


My class is this:

class Measures(Model):
__tablename__= 'xcelera_measures'
id= Column(Numeric,primary_key=True)
 studyidk= Column(Numeric, ForeignKey('xcel.studyidk'))
xceleragroup= relationship("Xcelera")
 explainstring= Column(String(255))
 mrn= Column(String(255))
 value= Column(Numeric)

 __mapper_args__= {
 "order_by": [mrn]
 }


and 'value' is the property/attribute that I want to also have a 
truncated version available in the class.


I tried adding this to the class value_new = column_property("%.3f" % 
value())


but got an error that

value_new = column_property("%.3f" % value)


"%" is a Python function, that doesn't execute on the database.  This 
works as a normal Python descriptor:


class MyClass(Base):
# ...

@property
def value_new(self):
return "%.3f" % self.value









TypeError: float argument required, not Column

I also tried this as a hybrid_property, but I don't think I was using it 
correctly.


All I want to do is have the truncated version of my attribute available 
in my class.


Thanks!

Greg--


--
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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Groups "sqlalchemy" group.
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.
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--
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Re: [sqlalchemy] Re: How to format class property as another accessible property

[Greg Silverman]

Hi,
Thanks for pointing that out. It's still throwing the same error, even when
changed. Does not seem to like passing the column name to the
column_property method.

Greg--



On Wed, Jun 7, 2017 at 3:30 PM, Jonathan Vanasco 
wrote:

> These are two different lines of code.  The second one looks correct.
>
>> value_new = column_property("%.3f" % value())
>> value_new = column_property("%.3f" % value)
>>
> --
> 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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-- 
Greg M. Silverman

 ›  flora-script  ‹
 ›  grenzi.org  ›

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Migration fails when changing to single table inheritance

[Michael]

Hi all, I have a class called MediaChapter(Base), which I've refactored 
into MediaBase(Base) and MediaChapter(MediaBase) When I run the migration, 
I see:

psycopg2.IntegrityError: insert or update on table "mediachapter" violates 
foreign key constraint "fk_mediachapter_id_mediabase"
DETAIL:  Key (id)=(570) is not present in table "mediabase".



I'm not sure exactly what this means because I create a mediabase.id.

I did
ws-alembic -c kjvrvg/conf/development.ini -x packages=all revision --auto -m 
"MediaBase-MediaChapter subclassing"


-- SUCCESS

then
ws-alembic -c kjvrvg/conf/development.ini -x packages=all upgrade head 


-- FAILED


Here are my models, MediaBase:

class MediaBase(Base):
#: The table in the database
__tablename__ = "mediabase"

#: Database primary key for the row (running counter)
id = Column(Integer, autoincrement=True, primary_key=True)

# table inheritance
media_type = Column(String(32), nullable=False)

#: Publicly exposed non-guessable
uuid = Column(UUID(as_uuid=True), default=uuid4)

localizedname = Column(Unicode(128), default=None)

#: url
url = Column(Unicode(384), default=None)

# full iso language-locale identifier i.e. zh-Hans-US
language_id = Column(String(16), default=None)

# name of the person presenting the material
presenter_name = Column(Unicode(64), default=None)
source_material = Column(Unicode(128), default=None)

# table inheritance
__mapper_args__ = {'polymorphic_on': media_type}

def __repr__(self):
"""Shell and debugger presentation."""
return '{} ({}) {} <{}>'.format(self.localizedname, self.language_id
, str(self.uuid), self.url)

def __str__(self):
"""Python default and admin UI string presentation."""
return '{} ({}) presenter: {} source: {}  <{}>'.format(self.
localizedname, self.language_id, self.presenter_name, self.source_material, 
self.url)




and MediaChapter:

class MediaChapter(MediaBase):

#: The table in the database
__tablename__ = "mediachapter"

__mapper_args__ = {'polymorphic_identity': 'chapter'}

id = Column(Integer, ForeignKey('mediabase.id'), primary_key=True)

#: Which chapter this media is part of
chapter_id = Column(Integer, ForeignKey('chapter.id'))
chapter = relationship("Chapter", back_populates="mediachapter")




and finally here is the auto-generated migration. I put all files in a 
github Gist.

https://gist.github.com/mazz/7d63e521316859f4ae852e5cea5d84eb



Any suggestions?
Mazz


"""MediaBase-MediaChapter subclassing

Revision ID: a00980918d75
Revises: e74ba4203098
Create Date: 2017-06-07 16:10:29.807437

"""

# revision identifiers, used by Alembic.
revision = 'a00980918d75'
down_revision = 'e74ba4203098'
branch_labels = None
depends_on = None

import datetime
import websauna.system.model.columns
from sqlalchemy.types import Text  # Needed from proper creation of JSON 
fields as Alembic inserts astext_type=Text() row

from alembic import op
import sqlalchemy as sa
from sqlalchemy.dialects import postgresql

def upgrade():
# ### commands auto generated by Alembic - please adjust! ###
op.create_table('mediabase',
sa.Column('id', sa.Integer(), nullable=False),
sa.Column('media_type', sa.String(length=32), nullable=False),
sa.Column('uuid', postgresql.UUID(as_uuid=True), nullable=True),
sa.Column('localizedname', sa.Unicode(length=128), nullable=True),
sa.Column('url', sa.Unicode(length=384), nullable=True),
sa.Column('language_id', sa.String(length=16), nullable=True),
sa.Column('presenter_name', sa.Unicode(length=64), nullable=True),
sa.Column('source_material', sa.Unicode(length=128), nullable=True),
sa.PrimaryKeyConstraint('id', name=op.f('pk_mediabase'))
)
op.alter_column('group', 'created_at',
   existing_type=postgresql.TIMESTAMP(timezone=True),
   type_=websauna.system.model.columns.UTCDateTime(),
   existing_nullable=True)
op.alter_column('group', 'updated_at',
   existing_type=postgresql.TIMESTAMP(timezone=True),
   type_=websauna.system.model.columns.UTCDateTime(),
   existing_nullable=True)
op.create_foreign_key(op.f('fk_mediachapter_id_mediabase'), 
'mediachapter', 'mediabase', ['id'], ['id'])
op.drop_column('mediachapter', 'source_material')
op.drop_column('mediachapter', 'presenter_name')
op.drop_column('mediachapter', 'localizedname')
op.drop_column('mediachapter', 'url')
op.drop_column('mediachapter', 'uuid')
op.drop_column('mediachapter', 'language_id')
op.alter_column('user_activation', 'created_at',
   existing_type=postgresql.TIMESTAMP(timezone=True),
   type_=websauna.system.model.columns.UTCDateTime(),
   existing_nullable=True)
op.alter_column('user_activation', 'expires_at',
   existing_type=postgresql.TIMESTAMP(timezone=True),
   

[sqlalchemy] Re: How to format class property as another accessible property

[Jonathan Vanasco]

These are two different lines of code.  The second one looks correct. 

> value_new = column_property("%.3f" % value())
> value_new = column_property("%.3f" % value)
>

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SQLAlchemy - 
The Python SQL Toolkit and Object Relational Mapper

http://www.sqlalchemy.org/

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[sqlalchemy] How to format class property as another accessible property

[GMS]

I am sure this is easier than I am making it, but I just want to add a 
property to a class so that decimal representations get truncated at 3 
decimal digits.

My class is this:

class Measures(Model):
__tablename__ = 'xcelera_measures'
id = Column(Numeric, primary_key=True)
studyidk = Column(Numeric, ForeignKey('xcel.studyidk'))
xceleragroup = relationship("Xcelera")
explainstring = Column(String(255))
mrn = Column(String(255))
value = Column(Numeric)

__mapper_args__ = {
"order_by": [mrn]
}


and 'value' is the property/attribute that I want to also have a truncated 
version available in the class. 

I tried adding this to the class value_new = column_property("%.3f" % 
value())

but got an error that

value_new = column_property("%.3f" % value)

TypeError: float argument required, not Column

I also tried this as a hybrid_property, but I don't think I was using it 
correctly.

All I want to do is have the truncated version of my attribute available in 
my class.

Thanks!

Greg--


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http://www.sqlalchemy.org/

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