fix polymorphic tenant

[hazelsparrow]

This PR fixes an issue with polymorphic tenants where the polymorphic tenant id would not be set correctly.

1. In the before_validation callback defined in lib/acts_as_tenant/model_extensions.rb:136, the original implementation of this gem (before polymorphic tenant was introduced in Allow polymorphic tenant #169) would set the tenant id to the current tenant id. For polymorphic tenants, a similar assignment would only take place if the fields #{fkey} and #{polymorphic_type} are nil, which is not consistent with the previous implementation. This PR removes the if conditionals.

2. In the same callback on line 139 there is a bug:

m.send("#{fkey}=".to_sym, ActsAsTenant.current_tenant.class.to_s)

should read

m.send("#{fkey}=".to_sym, ActsAsTenant.current_tenant.id)

This is fixed in this PR.

3. Test in spec/acts_as_tenant/model_extensions_spec.rb:226 creates two models under the same tenant (@project), and yet expects only one model in the scope of the current tenant. The reason that test is (in my opinion) a false positive is because of the way the second model is created (through an association on @article) and the if conditionals mentioned above. To solve this problem, this PR wraps creating the second model in an ActsAsTenant.with_tenant(@article) block.

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A few additional comments:

• if conditionals mentioned above, and the test that passes because of them, basically allow you to keep a cached instance of an Article scoped to tenant A, switch to tenant B, and save a new PolymorphicTenantComment scoped to tenant A while tenant B is active. It seems to me that this defeats the whole purpose of this gem, please correct me if I'm wrong.

• You might wonder why the bug mentioned above never manifested itself. It's because the assignments in the before_validation callback are never executed, since the #{fkey} and #{polymorphic_type} are already present (they come from default_scope that gets executed as soon as you do .new on an ActiveRecord), and there's those if conditionals that would not override them if they're set.

[excid3]

Not sure if this is still an issue. I copied in the tests to master and wasn't able to recreate the issue.