Under what circumstances would db.define_table() return None

[Andrew Rogers]

This code working fine but now it fails because the db.define_table() returns None.

table = db.define_table('DatabaseModel', Field('TableName'))  # This is not working now
for t in db.tables:
    table.update_or_insert(TableName=t)

The only thing that I think I have changed that might have affected it was setting migrate = false in appconfig.ini. I have changed it back but to no avail. 

What could stop db.define_table from returning a table?

(I am using this to create an in-memory table which I populate with a list of actual tables.)

Thanks.

PS: https://stackoverflow.com/questions/62908908/under-what-circumstances-would-db-define-table-return-none

[villas]

You don't mention...

• Which DB adapter you are using
• Why just one of your tables is expected to be an in-memory table and the others not
• Why you don't simply maintain the list of tables in a list(), or dict() or some other in-memory structure
  

In any case, maybe this idea might help...

db = DAL("sqlite://storage.sqlite") # or whichever DB you are using

dbmemo = DAL("sqlite:memory")

dbmemo.define_table('DatabaseModel', Field('TableName'))

for t in db.tables:

    dbmemo.DatabaseModel.update_or_insert(TableName=t)

[Andrew Rogers]

Thanks for your response Villas. My reason for this approach is that i have a lot of code that expects a table object and i am trying to avoid having to modify it to handle the a different format.

Anthony on Stack Exchange found my error. He said:

"You probably also set DAL(..., lazy_tables=True), in which case, db.define_table() returns None rather than a Table object, as the table is not actually created until first accessed via db.tablename.

Given your code, there is no benefit to setting lazy_tables=True, as all tables are accessed (and therefore created) immediately after definition anyway."

[villas]

That's great Andrew. 

BTW great to see that Anthony is helping - he is someone who really knows the nuts and bolts of web2py!

[AGRogers]

That's for sure! His stack exchange posts really helped me get around some problems early on... and now :-) I should pray for a special blessing for him tomorrow 🙏 

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