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Contents
# frozen_string_literal: true
module ActiveRecord
module Middleware
# 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
# }
class ShardSelector
def initialize(app, resolver, options = {})
@app = app
@resolver = resolver
@options = options
end
attr_reader :resolver, :options
def call(env)
request = ActionDispatch::Request.new(env)
shard = selected_shard(request)
set_shard(shard) do
@app.call(env)
end
end
private
def selected_shard(request)
resolver.call(request)
end
def set_shard(shard, &block)
ActiveRecord::Base.connected_to(shard: shard.to_sym) do
ActiveRecord::Base.prohibit_shard_swapping(options.fetch(:lock, true), &block)
end
end
end
end
end
Version data entries
29 entries across 29 versions & 6 rubygems