Ruby on Rails 2.1 - Nested with-scope


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The following example shows how we can nest with_scope to fetch different results based on requirements.

# SELECT * FROM employees
# WHERE (salary > 10000)
# LIMIT 10
# Will be written as 
Employee.with_scope(
   :find => { :conditions => "salary > 10000",
   :limit => 10 }) do
   Employee.find(:all)
end

Now, check another example that shows how scope is cumulative.

# SELECT * FROM employees
# WHERE ( salary > 10000 )
# AND ( name = 'Jamis' ))
# LIMIT 10
# Will be written as
Employee.with_scope(
   :find => { :conditions => "salary > 10000",
   :limit => 10 }) do
   Employee.find(:all) 
   Employee.with_scope(
      :find => { :conditions => "name = 'Jamis'" }) do
      Employee.find(:all) 
   end
end

The following example shows how the previous scope is ignored.

# SELECT * FROM employees
# WHERE (name = 'Jamis')
# is written as
Employee.with_scope(
   :find => { :conditions => "salary > 10000",
   :limit => 10 }) do
   Employee.find(:all) 
   Employee.with_scope(
      :find => { :conditions => "name = 'Jamis'" }) do
      Employee.find(:all) 
   end
   # all previous scope is ignored
   Employee.with_exclusive_scope(
      :find => { :conditions => "name = 'Jamis'" }) do
      Employee.find(:all)
   end
end

rails-quick-guide.htm

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