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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