Daniel Miller пишет:
>
> Basil Shubin wrote:
>> Michael Bayer пишет:
>>> this example is confusing the Table object with a mapped class.
>>>
>>> selecting off a table with the FOR UPDATE clause added looks like:
>>>
>>> result = table.select(localTowns.c.id==itemid, for_update=True)
>>>
>>> "lockmode" is an ORM-level concept when youre dealing with mapped
>>> classes.
>> Thanks, now I realise how to use it. But here is another problem, how I
>> can check if the appropriate row was selected for update? It's needed
>> because I want show error message box in a case where row is in update
>> status. As I see if I try access already selected row it just hang up
>> until the row was released, alas, no exception was raised. So my
>> question is how I can prevent user from selecting the row that was
>> selected by other, how I can do this by programming?
>>
>
> I have to agree with Michael here, you probably shouldn't be using
> pessimistic locking. I'm a PostgreSQL user, so I'll tell you how I would do
> it with that. You'll have to translate this to use it with MySQL (I think
> that's what you said you're using). Also, this approach will only work if you
> control all access to the table (i.e. only if no external applications will
> be updating the table--otherwise you'll need to use pessimistic locking).
> Also, this solution will only work for tables with with an integer primary
> key, although it could be adapted to work with any table by creating
> additional lock tables for each primary key type.
>
> Create a table in your database to hold locks. It should be something like
> this:
>
> CREATE TABLE locks (
> table_name varchar,
> locked_row_id int,
> PRIMARY KEY (table_name, locked_row_id)
> );
Is it possible to create table like above via SQLAlchemy? For
construction like this:
self.locks = Table('locks', self.metadata,
Column('table_name', Unicode(15)),
Column('locked_row_id', Integer),
Column('table_name', 'locked_row_id',
primary_key=True))
I got ab error:
File "/usr/lib/python2.4/site-packages/sqlalchemy/schema.py", line
284, in create
self.metadata.create_all(connectable=connectable,
checkfirst=checkfirst, tables=[self])
File "/usr/lib/python2.4/site-packages/sqlalchemy/schema.py", line
862, in create_all
connectable.create(self, checkfirst=checkfirst, tables=tables)
File "/usr/lib/python2.4/site-packages/sqlalchemy/engine/base.py",
line 413, in create
self._run_visitor(self.dialect.schemagenerator, entity,
connection=connection, **kwargs)
File "/usr/lib/python2.4/site-packages/sqlalchemy/engine/base.py",
line 437, in _run_visitor
element.accept_schema_visitor(visitorcallable(self, conn.proxy,
connection=conn, **kwargs), traverse=False)
File "/usr/lib/python2.4/site-packages/sqlalchemy/schema.py", line
882, in accept_schema_visitor
visitor.visit_metadata(self)
File "/usr/lib/python2.4/site-packages/sqlalchemy/ansisql.py", line
637, in visit_metadata
table.accept_schema_visitor(self, traverse=False)
File "/usr/lib/python2.4/site-packages/sqlalchemy/schema.py", line
268, in accept_schema_visitor
return visitor.visit_table(self)
File "/usr/lib/python2.4/site-packages/sqlalchemy/ansisql.py", line
658, in visit_table
self.append("\t" + self.get_column_specification(column,
first_pk=column.primary_key and not first_pk))
File
"/usr/lib/python2.4/site-packages/sqlalchemy/databases/mysql.py", line
435, in get_column_specification
t = column.type.engine_impl(self.engine)
AttributeError: 'str' object has no attribute 'engine_impl'
OnInit returned false, exiting...
--
Basil Shubin
Freelance Software Developer
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