I have had to integrate a rails application with a legacy database. I
must say it worked out rather well, but now I need to create a separate
Rails app that also needs to use much of the same functionality that the
first app did. I started to separate out all the code I used in the
first app into a plugin that I can include in the new application (and
any additional in the future). With the exception of a separate
database connection in database.yml all the code for this are simple
ActiveRecord models. Is this the best direction for this?
The other issue I started to notice was that I should probably use some
sort of namespaces to prevent class conflicts. I started prefixing all
the models, currently 10 models in 10 files, with “Legacy::”, but that
broke all the associations between these models. Of which, there are a
lot. Is there a better way to handle this too?
As on last bonus, as all these models use a custom database connection
is it best to just add that connection to the database.yml file, or
(can) should I put that connection information somewhere else so it is
better associated with the plugin itself?
database connection in database.yml all the code for this are simple
ActiveRecord models. Is this the best direction for this?
I agree. Plugins are perfect for grouping together sets of model
classes.
The other issue I started to notice was that I should probably use some
sort of namespaces to prevent class conflicts. I started prefixing all
the models, currently 10 models in 10 files, with “Legacy::”, but that
broke all the associations between these models. Of which, there are a
lot. Is there a better way to handle this too?
Yes, in your ActiveRecord associations specify “:class_name”,
something like this:
class Foo < ActiveRecord::Base
has_many :bar, :class_name => ‘Legacy::Bar’, :foreign_key =>
‘foo_id’
end
This is only necessary for models that aren’t part of the namespace:
all the “Legacy::” models can associate with each other without any
prefixes.
As on last bonus, as all these models use a custom database connection
is it best to just add that connection to the database.yml file, or
(can) should I put that connection information somewhere else so it is
better associated with the plugin itself?
I don’t know if this would work best for you, but one approach would
be to make a parent class for all your other models. Set the database
connection in that parent class.
One caveat: if your ActiveRecord associations are across models in
different databases you might have problems, because of the way Rails
does joins etc. behind the scenes. So if you encounter problems you
can do your relationships manually instead of using ActiveRecord’s
associations: you can write methods in your models that find
associated records, etc.
The other issue I started to notice was that I should probably use some
sort of namespaces to prevent class conflicts. I started prefixing all
the models, currently 10 models in 10 files, with “Legacy::”, but that
broke all the associations between these models. Of which, there are a
lot. Is there a better way to handle this too?
Yes, in your ActiveRecord associations specify “:class_name”,
something like this:
class Foo < ActiveRecord::Base
has_many :bar, :class_name => ‘Legacy::Bar’, :foreign_key =>
‘foo_id’
end
This is only necessary for models that aren’t part of the namespace:
all the “Legacy::” models can associate with each other without any
prefixes.
When I first did set it up I didn’t put all the models in a subfolder
and that caused some complaints while testing. Once I moved all the
models into a subfolder the prefix issue disappeared, within those
models that is.
As on last bonus, as all these models use a custom database connection
is it best to just add that connection to the database.yml file, or
(can) should I put that connection information somewhere else so it is
better associated with the plugin itself?
I don’t know if this would work best for you, but one approach would
be to make a parent class for all your other models. Set the database
connection in that parent class.
That is exactly what I did. All the parent class has in it is an
“establish_connection” call and all the models inherit from it. My
question was more related to where the connection information (user,
host, password) should reside. As these applications will only be
internal I don’t think having this info in the database.yml is such a
bad idea.
One caveat: if your ActiveRecord associations are across models in
different databases you might have problems, because of the way Rails
does joins etc. behind the scenes. So if you encounter problems you
can do your relationships manually instead of using ActiveRecord’s
associations: you can write methods in your models that find
associated records, etc.
Thanks for the reminder. I definitely had to deal with this when
building the original application.
I just want to say how awesome this is turning out. It only took about
20 minutes to get everything setup and working. Now, just to get the
original application switched to use the new plugin.