Hi Mike,
I have created an issue for pyodbc
: https://github.com/mkleehammer/pyodbc/issues/835#issuecomment-708930870
I've gotten really good feedback there from Microsoft, and a fix has been
proposed that works:
*"You can try to use setinputsizes on your parameter to tell it to send as
varchar(max): cursor.setinputsizes([(pyodbc.SQL_WVARCHAR,0,0),])"*
I'm by no means an SQLAlchemy expert, but shouldn't the pyodbc dialect be
updated to support varchar(max)using the proposed method? If not, how can I
execute cursor.setinputsizes([(pyodbc.SQL_WVARCHAR,0,0),]) using
SQLAlchemy, so that I can make use of varchar(max)in my application?
Can you recommend a hotfix for using varchar(max)in current SQLAlchemy
applications that need to handle Unicode supplementary characters (_SC)?
I appreciate really appreciate your help.
Best regards
Nicolas
On Wednesday, October 14, 2020 at 3:36:11 PM UTC+2 Mike Bayer wrote:
>
>
> On Wed, Oct 14, 2020, at 5:35 AM, Nicolas Lykke Iversen wrote:
>
> Hi Mike,
>
> I've now tested inserting strings with more than 2000 characters using
> Azure Data Studio (SQL Server GUI) and everything works.
>
> Furthermore, I've tested pyodbc (DBAPI) directly, and it only fails when
> inserting such strings using parameterised SQL queries (it succeeds without
> using parametrised queries).
>
>
> that would be expected because all the datatype-related issues occur when
> bound parameters are passed.
>
>
>
> You can see my POC below, if you have any interest.
>
> I guess it should be submitted as a bug to pyodbc... Do you know if I can
> disable parametrisation for certain SQL queries in SQLAlchemy?
>
>
> there is not and this is definitely an issue that has to be solved at the
> pyodbc level, either a bug on their end or something in your configuration
> that has to be changed.
>
>
>
>
>
> Best regards (and thanks for your help and support!!!)
> Nicolas
>
> *System info*:
> python v. 3.8.5
> pyodbc v. 4.0.30
> msodbcsql17 v. 17.6.1.1
>
> *POC*:
> import sys
> import pyodbc
>
> host = 'tcp:127.0.0.1,1433'
> db = 'pyodbc_test'
> user = 'sa'
> pwd = 'P@ssw0rd'
>
> print('started')
>
> cnxn = pyodbc.connect('DRIVER={ODBC Driver 17 for SQL
> Server};SERVER='+host+';DATABASE='+'master'+';UID='+user+';PWD='+ pwd,
> autocommit=True)
> cursor = cnxn.cursor()
>
> try:
> cursor.execute(f'CREATE DATABASE {db} COLLATE
> Latin1_General_100_CI_AS_SC')
> except pyodbc.ProgrammingError as e:
> pass # database exists
>
> cursor.execute(f'USE {db}')
>
> try:
> cursor.execute("""
> CREATE TABLE msg (
> id int identity(1,1) not null,
> content varchar(max) not null
> );""")
> except pyodbc.ProgrammingError as exc:
> pass # table exists
>
> content = 2000 * 'A'
>
> cursor.execute(f"""
> INSERT INTO msg (content)
> VALUES ('{content}')""")
> print(f'non-param: {len(content)=}: success')
>
> sql = f"""
> INSERT INTO msg (content)
> VALUES (?)"""
> cursor.execute(sql, (content))
> print(f'param: {len(content)=}: success')
>
> content = 2001 * 'A'
>
> cursor.execute(f"""
> INSERT INTO msg (content)
> VALUES ('{content}')""")
> print(f'non-param: {len(content)=}: success')
>
> # this fails!
> sql = f"""
> INSERT INTO msg (content)
> VALUES (?)"""
> cursor.execute(sql, (content))
> print(f'param: {len(content)=}: success')
>
>
> #cursor.execute('SELECT * FROM msg')
> #rows = cursor.fetchall()
> #for r in rows:
> # print(r)
>
> print('finished')
>
>
>
> On Wednesday, October 14, 2020 at 12:43:25 AM UTC+2 Mike Bayer wrote:
>
>
>
> On Tue, Oct 13, 2020, at 4:57 PM, Nicolas Lykke Iversen wrote:
>
> Thank you, Mike - very much appreciated!
>
> Just to be clear, pyodbc is not a driver, it’s a ODBC-compliant DBAPI,
> right? I separately downloaded a driver for SQL Server from Microsoft,
> which pyodbc makes use of.
>
>
> right the pyodbc is the DBAPI in this case, which we usually refer to as a
> "driver" but in the case of ODBC the "driver" is more specifically the
> separate ODBC driver component.
>
>
> Do you suggest that changing pyodbc to another SQL Server DPAPI would
> solve the problem?
>
>
> I suggest that if there is no issue with the query you're running outside
> of the context of pyodbc that you submit an issue to pyodbc at
> https://github.com/mkleehammer/pyodbc/issues . However I was able to
> find a discussion thread about your error message that seemed to be
> independent of ODBC.
>
>
>
>
>
> If so, can you recommend another DBAPI for SQL Server? Or do you think
> that the problem is caused by Microsoft’s driver?
>
>
> pyodbc is the only supported driver for SQL Server that exists now for
> Python. You also definitely want to use Microsoft's ODBC drivers so
> you're already there.
>
>
>
> I’m pretty sure SQL Server works fine when accessed using .NET, otherwise
> the Internet would be full of complaints regarding not being able to insert
> +2000 characters in a varchar(max).
>
>
> you'd want to see if the same ODBC driver and options are in use in that
> scenario.
>
>
>
>
>
> Best regards
> Nicolas
>
>
> On Tue, 13 Oct 2020 at 22.22, Mike Bayer <mik...@zzzcomputing.com> wrote:
>
>
>
>
> On Tue, Oct 13, 2020, at 10:50 AM, Nicolas Lykke Iversen wrote:
>
> Hi SQLAlchemy,
>
> *System information:*
>
> - Mac OS X v. 10.15.7
> - Python v. 3.8.5
> - SQLAlchemy v. 1.3.19
> - MS SQL Server 2017 and 2019 (both Enterprise and Docker images e.g.
> mcr.microsoft.com/mssql/server:2019-latest)
>
> *Problem*:
> I have an issue with inserting strings with a length greater than 2000
> into columns with a datatype of Text, VARCHAR, or NVARCHAR using MS SQL
> Server 2017 and 2019.
>
> I've checked the MS SQL Server and it creates it column properly with e.g.
> a datatype of varchar(max)for Text and VARCHAR, which should be able to
> store strings with a size up to 2 GB according to Microsoft documentation.
>
> Furthermore, I've tried using other collations, but I need _SC (supplementary
> character) support for my applications, so I cannot drop it, and adding _UTF8
> (UTF-8) doesn't solve the problem either.
>
> Why am I not allowed to store strings with a size greater than 2000?
>
>
> I'm not really sure, this has to do with a behavior of SQL Server and/or
> your ODBC driver. a google search finds fairly scant results but there is
> a long discussion regarding this error here:
> https://www.sqlservercentral.com/forums/topic/collation-error-when-adding-distributer
>
>
>
>
>
>
>
>
> And why is SQLAlchemy displaying that error message, when trying to insert
> plain ASCII text ("AAAA...")?
>
>
> SQLAlchemy runs SQL statements using a method called "cursor.execute()",
> which is a feature of the DBAPI (database driver) in use. As your error
> message indicates you're using the pyodbc driver, this method is documented
> here:
> https://github.com/mkleehammer/pyodbc/wiki/Cursor#executesql-parameters
>
> The DBAPI execute() method, and most of the other DBAPI methods, can throw
> exceptions if something goes wrong. SQLAlchemy has the policy that if it
> encounters such an exception when it calls cursor.execute(), it wraps it in
> a SQLAlchemy-specific version of that exception (named the same) and then
> throws it.
>
> In other words you're using a driver called pyodbc that's creating this
> error. SQLAlchemy just propagates it for you but otherwise has nothing to
> do with how it's produced.
>
>
>
>
> I would really appreciate some guidance on how to solve this problem. What
> could be causing it?
>
> *Error*:
> sqlalchemy.exc.ProgrammingError: (pyodbc.ProgrammingError) ('42000',
> "[42000] [Microsoft][ODBC Driver 17 for SQL Server][SQL Server]Cannot
> convert to text/ntext or collate to 'Latin1_General_100_CI_AS_SC' because
> these legacy LOB types do not support UTF-8 or UTF-16 encodings. Use types
> varchar(max), nvarchar(max) or a collation which does not have the _SC or
> _UTF8 flags. (4189) (SQLParamData)")
> [SQL: INSERT INTO msg (content) OUTPUT inserted.id VALUES (?)]
> [parameters:
> ('AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
>
> ... (1703 characters truncated) ...
> AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA',)]
> (Background on this error at: http://sqlalche.me/e/13/f405)
>
>
> *Program (POC)*:
> import logging
> import sqlalchemy
> from sqlalchemy import Column, Text, Integer, NVARCHAR, VARCHAR
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy.orm import sessionmaker
>
> logging.root.setLevel(logging.DEBUG)
>
> Base = declarative_base()
>
>
> class Msg(Base):
> __tablename__ = 'msg'
>
> id = Column(Integer, primary_key=True, autoincrement=True)
> content = Column(VARCHAR, nullable=False)
>
>
> user = 'sa'
> pwd = 'P@ssw0rd'
> host = 'localhost'
> port = 1433
> db = 'test'
>
> logging.info('started.')
>
> engine = sqlalchemy.create_engine(
>
> f'mssql+pyodbc://{user}:{pwd}@{host}:{port}/{db}?driver=ODBC+Driver+17+for+SQL+Server',
> pool_size=5,
> max_overflow=10,
> pool_pre_ping=True,
> isolation_level='READ_UNCOMMITTED',
> pool_recycle=900,
> echo=False,
> connect_args={'connect_timeout': 10})
>
> Base.metadata.create_all(engine)
>
> Session = sessionmaker(bind=engine, autoflush=False, autocommit=False)
> session = Session()
>
> for i in range(10000):
> try:
> msg = Msg(content='A' * i)
> session.add(msg)
> session.commit()
> except Exception as exc:
> logging.exception(f'fail: {i=}: {exc}')
> break
> else:
> logging.info(f'success: {i=}')
>
> logging.info('done.')
>
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
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>
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>
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>
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>
> http://www.sqlalchemy.org/
>
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http://www.sqlalchemy.org/
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