Metakit help

[Gordon McMillan]

David LeBlanc wrote:

> Working more with Metakit, i'm finding that there is some information
> not in the documentation, so I have a few questions:
> 
> I think I figured out how to create a nested schema, but not how to
> insert or append a row with nested data - how is that done?

Insert / append the containing row. It will have an
empty subview, and row.subview is a view. Insert / append
as needed.
 
> How do you get a view from a pre-existing database?

storage.view('viewname')

> Can you modify the schema of an existing database? How?

Do another storage.getas(...). Adjusting the type
of a column is (almost) like dropping and adding
the column.
 
> How do you put a pickle in a database? 

Put it in as a B (binary string).
 
> Are the various attributes of
> that pickle accessable while it's in metakit storage? How about the
> pickled object's attributes?

To Metakit, it's just a binary string.

> How would you enforce a uniqueness constraint on a key field?

Depends. If it's a what in RDBMS-land you'd call a 
primary key, I'd make it the first column and 
make sure it's sorted (easy when the view's empty :-)).

if isnew:
  v = db.getas('myview[key:S,...]')
else:
  v = db.view('myview')
v = v.ordered(1)

Now v.find(...) will use a binary search.

If your key is just a unique key, I'd build an
index view '_myview[key:S,ndx:I]'.

Either way, it's pretty easy to wrap the 
view so the constraint is enforced. (These
aren't new-style types yet, so you can't
subclass.)

If your view exists:
 v = storage.view('myview')
 v[:] = v.sort()
 storage.commit()

And join the metakit list:
 http://www.equi4.com/mailman/listinfo/metakit

-- Gordon
http://www.mcmillan-inc.com/