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Class: ActiveRecord::Middleware::DatabaseSelector::Resolver

Do not use. This class is for internal use only.

Overview

The Resolver class is used by the ::ActiveRecord::Middleware::DatabaseSelector middleware to determine which database the request should use.

To change the behavior of the Resolver class in your application, create a custom resolver class that inherits from Resolver and implements the methods that need to be changed.

By default the Resolver class will send read traffic to the replica if it’s been 2 seconds since the last write.

Constant Summary

Class Method Summary

Instance Attribute Summary

Instance Method Summary

Constructor Details

.new(context, options = {}) ⇒ Resolver

[ GitHub ] 

  


# File 'activerecord/lib/active_record/middleware/database_selector/resolver.rb', line 26



def initialize(context, options = {})
  @context = context
  @options = options
  @delay = @options && @options[:delay] ? @options[:delay] : SEND_TO_REPLICA_DELAY
  @instrumenter = ActiveSupport::Notifications.instrumenter
end


  







Class Method Details



  

    .call(context, options = {})  
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/middleware/database_selector/resolver.rb', line 22



def self.call(context, options = {})
  new(context, options)
end


  







Instance Attribute Details



  

    #context   (readonly)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/middleware/database_selector/resolver.rb', line 33



attr_reader :context, :delay, :instrumenter


  








  

    #delay   (readonly)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/middleware/database_selector/resolver.rb', line 33



attr_reader :context, :delay, :instrumenter


  








  

    #instrumenter   (readonly)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/middleware/database_selector/resolver.rb', line 33



attr_reader :context, :delay, :instrumenter


  








  

    #read_from_primary?  ⇒ Boolean  (readonly, private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/middleware/database_selector/resolver.rb', line 78



def read_from_primary?
  !time_since_last_write_ok?
end


  








  

    #time_since_last_write_ok?  ⇒ Boolean  (readonly, private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/middleware/database_selector/resolver.rb', line 86



def time_since_last_write_ok?
  Time.now - context.last_write_timestamp >= send_to_replica_delay
end


  







Instance Method Details



  

    #read(&blk)  
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/middleware/database_selector/resolver.rb', line 35



def read(&blk)
  if read_from_primary?
    read_from_primary(&blk)
  else
    read_from_replica(&blk)
  end
end


  








  

    #read_from_primary(&blk)   (readonly, private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/middleware/database_selector/resolver.rb', line 56



def read_from_primary(&blk)
  ActiveRecord::Base.connected_to(role: ActiveRecord.writing_role, prevent_writes: true) do
    instrumenter.instrument("database_selector.active_record.read_from_primary", &blk)
  end
end


  








  

    #read_from_replica(&blk)   (private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/middleware/database_selector/resolver.rb', line 62



def read_from_replica(&blk)
  ActiveRecord::Base.connected_to(role: ActiveRecord.reading_role, prevent_writes: true) do
    instrumenter.instrument("database_selector.active_record.read_from_replica", &blk)
  end
end


  








  

    #reading_request?(request)  ⇒ Boolean 
  



  

    
  





  


  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/middleware/database_selector/resolver.rb', line 51



def reading_request?(request)
  request.get? || request.head?
end


  








  

    #send_to_replica_delay   (private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/middleware/database_selector/resolver.rb', line 82



def send_to_replica_delay
  delay
end


  








  

    #update_context(response)  
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/middleware/database_selector/resolver.rb', line 47



def update_context(response)
  context.save(response)
end


  








  

    #write(&blk)  
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/middleware/database_selector/resolver.rb', line 43



def write(&blk)
  write_to_primary(&blk)
end


  








  

    #write_to_primary   (private)
  

  [ GitHub ]


  

  


# File 'activerecord/lib/active_record/middleware/database_selector/resolver.rb', line 68



def write_to_primary
  ActiveRecord::Base.connected_to(role: ActiveRecord.writing_role, prevent_writes: false) do
    instrumenter.instrument("database_selector.active_record.wrote_to_primary") do
      yield
    ensure
      context.update_last_write_timestamp
    end
  end
end