Class: ActiveRecord::Middleware::ShardSelector

Inherits:
Object
  • Object
show all
Defined in:
lib/active_record/middleware/shard_selector.rb

Overview

The ShardSelector Middleware provides a framework for automatically swapping shards. Rails provides a basic framework to determine which shard to switch to and allows for applications to write custom strategies for swapping if needed.

The ShardSelector takes a set of options (currently only `lock` is supported) that can be used by the middleware to alter behavior. `lock` is true by default and will prohibit the request from switching shards once inside the block. If `lock` is false, then shard swapping will be allowed. For tenant based sharding, `lock` should always be true to prevent application code from mistakenly switching between tenants.

Options can be set in the config:

config.active_record.shard_selector = { lock: true }

Applications must also provide the code for the resolver as it depends on application specific models. An example resolver would look like this:

config.active_record.shard_resolver = ->(request) {
  subdomain = request.subdomain
  tenant = Tenant.find_by_subdomain!(subdomain)
  tenant.shard
}

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(app, resolver, options = {}) ⇒ ShardSelector

Returns a new instance of ShardSelector.



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# File 'lib/active_record/middleware/shard_selector.rb', line 30

def initialize(app, resolver, options = {})
  @app = app
  @resolver = resolver
  @options = options
end

Instance Attribute Details

#options ⇒ Object (readonly)

Returns the value of attribute options.



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# File 'lib/active_record/middleware/shard_selector.rb', line 36

def options
  @options
end

#resolver ⇒ Object (readonly)

Returns the value of attribute resolver.



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# File 'lib/active_record/middleware/shard_selector.rb', line 36

def resolver
  @resolver
end

Instance Method Details

#call(env) ⇒ Object 



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# File 'lib/active_record/middleware/shard_selector.rb', line 38

def call(env)
  request = ActionDispatch::Request.new(env)

  shard = selected_shard(request)

  set_shard(shard) do
    @app.call(env)
  end
end