Sorry it took me so long to reply.
On 14/12/12 11:25, Jure Zitnik wrote:
On 12/13/12 4:17 PM, Gary Martin wrote:
On 13/12/12 13:41, Jure Zitnik wrote:
The idea we are playing with is that in addition to translating 3rd
party plugin DMLs (SELECT/INSERT/UPDATE/DELETE) (to present plugins
with a view of trac/bh resources as seen from the current product
scope), the DDLs (CREATE/ALTER/DROP) for the custom tables should
also be translated to support product scope(s) - this would be
accomplished by creating per product custom table(s), prefixing the
table name with product prefix. This (in combination with the
currently implemented SQL translation) would present product unaware
3rd party plugins with product scoped tables for both, trac/bh
tables and any custom table the plugin would create. References
between the tables would also work and the content of the tables
would always represent data based on the resources in the product
scope.
Naive approach would be to solve 3rd party custom table the same way
as trac/bh tables (by adding product column). This does not work for
two reasons:
- schema upgrades - if the plugin chooses to upgrade it's custom
table schema the usual way of doing this is to copy data to temp
table, drop original table (this would effectively drop data for all
products), recreate new table with changed schema and fill it from
temp table
- table schema changes - not really sure how to implement ALTER
TABLE if we modify the original schema (connected with the first
reason)
To summarize the idea:
1. for 3rd party plugins that are product unaware, any custom table
being created is namespaced to the product by prefixing the table
name with the product name (in a similar way as discussed resource
name columns). SQL translator functionality will need to be extended
to support DDL.
2. the SQL translator will be changed in such a way that it will
support the following table 'types':
- non-translated tables - tables that need no translation
(session, cache, attachments,...)
- trac/bh tables with product scope - these are tables with
product specific resource (enum, component, ticket, milestone,
version,...) - the product scope for these tables is implemented
using 'product' column
- 3rd party, product-unaware plugin custom tables - product scope
for these tables is implemented by prefixing the table name with
product prefix
3. changes to product unaware plugin install/upgrade process -
install/upgrade (IEnvironmentSetupParticipant) would need to be
invoked for all currently defined products (within that product
scope of course)
4. adding a new product would need to invoke 3rd party (product
unaware) plugin installation
How does that sound to everyone?
Thanks.. we definitely needed this to evaluate the solution properly!
I don't strictly mind what solution is implemented as long as we are
not going too far down a dead end. I would also generally prefer
whichever solution turned out to be simplest but that will be far
harder to judge.
Interestingly, if you are also looking at managing table names, it is
not inconceivable that you could add the product fields to the 3rd
party resource tables after all, as long as you were also prepared to
discover which fields should be unique together with product. One of
the possible dangers with this might be that a plugin is at some
point allowed to adjust the schema (obviously we wouldn't mean to
allow it - it would still be possible though) so it still might be
wise to change the table name anyway. There is the possible advantage
that it limits the differences in processing a little.
That (adding product column to 3rd party resources) was one of the
ideas that were evaluated. The problem with that approach is the
schema upgrade process that usually goes like this (even in trac itself):
1. copy data to temp table
2. drop original
3. create new table with changed schema
4. fill new table from temp table & drop temp table
The problem is step 2 (table drop) as there is no way of preventing
plugin from dropping the table regardless of the fact that the table
holds data for all product scopes and not just the current one.
I still don't see that as hugely different from translating the initial
creation of the table but there may well be more to keep track of than I
appreciate. The plugin upgrading all product scopes in a single step
does not seem to be the biggest issue as long as the product column is
maintained in each operation. Requirements that a plugin has on
sequences may also cause issues of course.
There is actually one final thing that seems to have been left
without any consideration, and that is whether we can get away with
allowing third party resources to be available across all scopes. I
assume that the initial implementations will start off this way anyway!
If we take the 'table name prefix' approach, 3rd party resource will
only be available in current product scope. Only product aware plugins
and bloodhound code will be able to access resources through all
scopes using the global database connection that will have the SQL
translator turned off. The interesting issue here is how to present
that 3rd party resource (scattered across multiple tables) through
global scope without requiring them to do UNION SELECTs on all tables.
We might provide helper functions for that though ... something to
think about but definitely not critical at the moment.
Well, what I was wondering is whether we would have something useful at
an intermediate stage if we only have product scoping on non-3rd party
resources. That would allow the initial implementation to ignore the
issues of the table name prefix which could slow our adoption of the
solution while all the work is in progress.
However, the global scope is certainly an interesting problem in the
multi-table solution. It may help if we assume that plugins would have
to be product-aware to have certain abilities in global scope but I have
no doubt that there will be plenty of complicating factors.
Cheers,
Gary
