I think it would be good to start a discussion to try to identify
what, if any, functionality is missing from the DAL in the context of
indices and constraints and whether it is worth filling the gap(s).
Terminology is not always consistent but I think that the following
definitions are worthwhile:
constraint: a mechanism to restrict the content of the database
index: a mechanism to allow speedier retrieval of content from the
database
>From a personal point of view, I consider the 'index' requirement
secondary to the 'constraint' requirement. So taking constraint
first:
PRIMARY: catered for as the primary key on web2py tables is always
'id'
UNIQUE: single column unique constraints are handled by the SQLField
'unique' attribute
Multi-column unique constraints are not handled
currently.
FOREIGN: handled by the 'references' attribute linking tables by 'id'
columns
Is it necessary to support other foreign constraints
(other columns, multiple columns)? Personally, I don't think so.
Other views?
CHECK: a database-level version of requires - not supported by MySQL
yet, I don't know about other dbs
Personally, I would vote to implement multi-column unique constraints
so that data integrity can be specified completely using DAL syntax
without the need for native SQL. I don't have a requirement for
different foreign keys and 'check' is perhaps sparsely supported.
RE indices:
I guess the basic requirement is to be be able to specify one or more
columns and for each column to specify ascending or descending
sequence.
The next step is to be able to specify each column as a substring.
Personally, I don't have an urgent need to support indices (other than
by executesql).
In retrospect, that seems like a long post to propose adding multi-
column unique constraints to the DAL but I'd be interested to read
other people's views.
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