I am using SQLObject (0.12.4, but could be later) with MySQL 5.1 as
the storage for a CherryPy based web app. I have a table "assembly"
which refers to another table "assembly_results"; the SQLObject class
def is something like:
class Assembly(SQLObject):
dbAssemblyResults = MultipleJoin('AssemblyResult',
joinColumn='db_assembly_id')
...
class AssemblyResult(SQLObject):
dbAssembly = ForeignKey('Assembly')
...
Both tables are InnoDB.
To upload new results, I need to generate a filename that includes an
index of the file, eg. the 5th result uploaded against an assembly is
named "05. Some file...". So I have the following:
# asmbly is an instance of Assembly
number = len(asmbly.dbAssemblyResults) + 1
new_name = construct_name(number, ...)
doc = create_document(new_name, ...)
# create_document returns an instance of another SQLObject subclass
AssemblyResult(doc, ...)
The trouble is that there's a race hazard here — two uploads at almost
the same time will see the same number of uploaded documents and I'll
end up with two file names with the same index.
The simplest way I could think of to make this safe is to lock the
assembly_result table for the duration of these calls (not
unreasonable in my situation), but I can't find support for table
locking in the SQLObject docs. Is it there, or should I use raw SQL
calls? Or is there a better way?
— Jason
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