Question

I am using Ruby on Rails 3.2.2 and I would like to know if in scope methods it is possible to “dynamically” join a table only if that table is not joined yet. That it, I have:

def self.scope_method_name(user)
  joins(:joining_association_name).where("joining_table_name.user_id = ?", user.id)
end

I would like to make something like the following:

# Note: the following code is just a sample in order to understand what I mean.
def self.scope_method_name(user)
  if table_is_joined?(joining_table_name)
    where("joining_table_name.user_id = ?", user.id)
  else
    joins(:joining_association_name).where("joining_table_name.user_id = ?", user.id)
  end
end

Is it possible / advised to make that? If so, how could / should I proceed?

---

I would like to use this approach in order to avoid multiple database table statements in INNER JOIN of SQL queries (in some cases it seems to make my SQL querying not working as expected since multiple table statements) and so to use the scope_method_name without caring related SQL query concerns (in my case, without caring to join database tables).

Note: It could raise SQL errors (for example, errors as-like “ActiveRecord::StatementInvalid: Mysql2::Error: Unknown column 'joining_table_name.user_id' in 'where clause'“) when you have not joined yet the database table (for example, this could happen when you run code like ClassName.scope_method_name(@user) without to previously join the joining_association_name and so without to join the related joining_table_name table).

Answer 1

Where is the method loaded? to check if an association has been loaded. You could try to use that.

if association_name.loaded?
   where("joining_table_name.user_id = ?", user.id)
else
   joins(:joining_association_name).where("joining_table_name.user_id = ?", user.id)
end