On 13/12/12 13:41, Jure Zitnik wrote:
Hi,
On 12/12/12 5:31 PM, Gary Martin wrote:
On 12/12/12 15:18, Jure Zitnik wrote:
2. Something that we might forgot: What about 3rd party plugin
tables that
reference multiproductized Trac tables?
Will probably need to proclaim these incompatible when more
than one
product is in effect?
Good point. To keep track of records from tables from third party
plugins, this approach doesn't quite work. I would have thought
that we would be better off using a separate table to keep track of
the resources that belong to a product. Is this another area that
has not been updated based on discussions?
The current SQL translator implementation would show 3rd party
plugins a view of translated tables that would only include
resources from the currently selected product scope. If the plugin
makes a reference to a resource by it's name everything should work
fine as the reference would be consistent each time when in that
specific product environment (as the plugin would always get the
same view of the database).
Things start breaking if there's a resource with the same name in
multiple products, unless the translator is changed to return names
with product namespace being prefixed to the actual resource name
for example. The plugins would get version name 'BH:1.0' instead of
'1.0' for example. Still, this doesn't solve the problem entirely as
the plugin (that's not aware of products) would end up (in it's own
tables) with references to different resources from different
products and maybe that's not exactly what's expected to happen...
Keeping track of resource belonging to a product using a separate
resource mapping table also unfortunately doesn't solve the issue.
We'd need to change the schema anyway as in the current database
model, all tables have 'name' column as their key. We could of
course reference the same resource from different products using the
separate mapping table but we'd be referencing the same record and
changing the name of that record would change the resource in all
products which is, at least imo, not what we want.
Ah yes, I forgot about my ideas for that. For the purposes of unique
keys I was thinking of including some kind of prefix as part of the
name - not necessarily the product namespace as we could consider it
better to leave this as a constant with a means to link the prefix to
the namespace.
As I wrote above, only prefixing names doesn't solve the issue. If we
have a product unaware plugin, that plugin should only see resources
from the current product scope and this (for trac/bh resources) is
currently accomplished by translating SQLs in such a way that the
plugin only sees a product specific view of resources. The problem
arises when the plugin stores references to that resources in their
own tables as it might end up (unless we do something about it) with
resource mixed from different products.
Let's say we have a custom table named 'sorted_milestones' with
columns 'milestone_name' and 'sequence' and database constraint that
'sequence' is unique. If plugins sees only resources (in this case
milestones) from one product at a time, constraint will fail as logic
sees only product scope specific part of milestones. When product
scope would change, the plugin sees completely different set of
milestones and has no way of knowing that certain sequences are
already 'taken'.
On the other hand, assuming we only prefix resources without filtering
them for multi-product unaware plugins would cause the user interface
for those plugins to show everything (every resource defined
regardless of product scope). In addition to that, it'd be hard (if
not impossible) to remove the prefix before showing that to the user.
Also, it's not exactly obvious that we can remove the prefix before
passing that to plugins/UI as we never know how those will be used
further down the line...
The problem with just adding fields to each model is not so much a
problem from the point of view of 3rd party plugins accessing those
models that are modified in such a way, but rather with those
resource tables that are added by the third party plugins.
Completely agree.
These would have to be modified to add the product to their tables
too. Is the suggestion that we do that modification for externally
defined resources or only provide the ability for specific plugins?
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.
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!
Cheers,
Gary
