问题
在跨库事务操作时，我们会用上这样的代码
A::User.transaction do
B::User.transaction do
C::User.transaction do
D::User.transaction do
end
end
end
end
有 A,B,C,D 四个库需要同时做事务操作（真实环境确实有这么多库）
为了完成以上的代码我这样做了一个简化
module Support
module Consistency
def self.transaction(*args, &block)
invalid_consts = args.select { |const| !const.respond_to?(:transaction)}
if invalid_consts.present?
raise "#{invalid_consts.map(&:to_s).join(',')}, they arent the sub class for ActiveRecord::Base".colorize(:red)
end
# TODO: I think there are better codes
cmd = ''
args.each do |const|
cmd << "#{const}.transaction {"
end
cmd << 'yield block'
args.each do |_|
cmd << '}'
end
eval cmd
end
end
end
Support::Consistency.transaction(A::User, B::User, C::User, D::User).transaction do
....
end
请问有更优雅的办法重构这块代码么？
mock 代码：
module A
class User
def self.transaction(&block)
puts "A::User transaction call #{block.call}"
end
end
end
module B
class User
def self.transaction(&block)
puts "B::User transaction call #{block.call}"
end
end
end
module C
class User
def self.transaction(&block)
puts "C::User transaction call #{block.call}"
end
end
end
module D
class User
def self.transaction(&block)
puts "D::User transaction call #{block.call}"
end
end
end
解决代码：
def tr(*args, &block)
bl = block
args.reverse.each {|arg|
# 这里不能使用 bl = -> { arg.transaction(&bl)}, 否则 lambda 的闭包作用会导致 SystemStackError
bl = create_tr_lambda(arg, &bl)
}
bl.call
end
def create_tr_lambda(arg, &block)
-> {arg.transaction(&block)}
end
tr(A::User, B::User, C::User, D::User) do
puts "begin transaction from D::user"
end
分析过程：
inner_bl = -> {}
d = -> {D::User.transaction(&inner_bl)}
c = -> {C::User.transaction(&d)}
b = -> {B::User.transaction(&c)}
a = -> {A::User.transaction(&b)}
def nested_transaction(*classes, &block)
classes.reverse_each.inject(block) {|nested_block, klass| -> { klass.transaction(&nested_block) } }.call
end
这个和 #1 楼 @kayakjiang 的逻辑是一样的。