SQLAlchemy Query not returning all of large text field

Question

First up, here's a little bit about my environment:

• Using MSSMS as my database management tool.
• Using Django 1.3
• Using SQLAlchemy

I have a text field in the database with no max length. There is text in it that is 890591 characters long.

When I retrieve this field using SQLAlchemy it is truncated to 64512 characters. I've tried it with several other large rows too, and it's always truncated to 64512.

SELECT @@TEXTSIZE returns some absurd value like 1.6 million, so that's not the problem. If I do SELECT DATALENGTH(field) it returns the correct 890591. So it doesn't seem to be the database, it seems to be SQLAlchemy. Or perhaps it could be some Python limit.

Any ideas? I seem to be at my wits end.

EDIT: Here's some more info that was requested:

OS: Debian 5.0.9

SQLAlchemy: 0.7.3

SQL: MS Sql Server 2008

DB Connection: mssql+pymssql://name:password@server/dbname

pymssql version: 1.0.2

Model in question:

class RACReport(Base):
    __tablename__ = 'RACReport'
    id                      = Column(properUUID(), primary_key=True, nullable=False, default=genuuid4, server_default=text('NEWID()'))
    client_id               = Column(properUUID(), ForeignKey(Client.id), nullable=False)
    rawdata                 = Column(Text(), nullable=True)
    rawtime                 = Column(DateTime(), nullable=True, default=datetime.datetime.now())
    processeddata           = Column(Text(), nullable=True)
    processedtime           = Column(DateTime(), nullable=True)
    reportstartdate         = Column(DateTime(), nullable=False)
    reportenddata           = Column(DateTime(), nullable=False)
    numberofdocs            = Column(Integer(), nullable=True)
RACReport.__table__.schema='rac'

class properUUID(st.TypeDecorator):
    impl = mssql.MSUniqueIdentifier
    def process_result_value(self, value, dialect):
        if value:
            return str(uuid.UUID(bytes_le=value))

def genuuid4():
    return str(uuid.uuid4())

rawdata and processdata are the two fields he is having the problem with.

Here's a test query and echo:

rac.session.query(rac.RACReport).filter(rac.RACReport.id=='8fb76cb7-d752-45af-a20a-3b85d5e7b8a6').all()

2011-11-17 09:39:46,890 INFO sqlalchemy.engine.base.Engine SELECT [RACReport_1].id AS [rac_RACReport_id], [RACReport_1].client_id AS [rac_RACReport_client_id], [RACReport_1].rawdata AS [rac_RACReport_rawdata], [RACReport_1].rawtime AS [rac_RACReport_rawtime], [RACReport_1].processeddata AS [rac_RACReport_processeddata], [RACReport_1].processedtime AS [rac_RACReport_processedtime], [RACReport_1].reportstartdate AS [rac_RACReport_reportstartdate], [RACReport_1].reportenddate AS [rac_RACReport_reportenddate] FROM rac.[RACReport] AS [RACReport_1] WHERE [RACReport_1].id = %(id_1)s 2011-11-17 09:39:46,890 INFO sqlalchemy.engine.base.Engine {'id_1': '8fb76cb7-d752-45af-a20a-3b85d5e7b8a6'}

Answer 1

I know little of *nix connectivity to SQL Server, but simple googling suggests that the issue is related to FreeTDS configuration:

1. A related question on SO: Data ended at 64512 characters - MSSQL // PHP // OPENSuSE // APACHE2.
2. Another Q&A extracted from here:

My text data are being truncated or are causing my client to break.

The text data type is different from char and varchar types. The maximum data length of a text column is governed by the textsize connection option. Microsoft claims in their documentation to use a default textsize of 4000 characters, but in fact their implementation is inconsistent. Sometimes text columns are returned with a size of 4 GB!

The best solution is to make sure you set the textsize option to a reasonable value when establishing a connection. For example:

1> set textsize 10000 
2> go 

See also the text size option in freetds.conf.

---

And just a side note: you seem to be using rather outdated version of pymssql.