[英]How to Conditionally Rollback a Transaction Using the PG Ruby Gem
I am currently taking a databases course and one of the lab questions has me stumped as to how to implement the above and indeed, if it was even possible.我目前正在学习数据库课程,其中一个实验室问题让我难以理解如何实现上述内容,甚至可能的话。 I have tried searching the docs but the transaction method defined is quite vague.
我曾尝试搜索文档,但定义的交易方法非常模糊。
This is the first time I have tried to do any database manipulation WITHOUT the comfort blanket of Rails and so I am a little lost.这是我第一次尝试在没有 Rails 舒适毯的情况下进行任何数据库操作,所以我有点迷茫。 I have managed to create a connection to my postgresql database and can execute statements, the final thing that I need to do is rollback a transaction based on a simple condition.
我已经成功地创建了一个到我的 postgresql 数据库的连接并且可以执行语句,我需要做的最后一件事是根据一个简单的条件回滚一个事务。
Allow me to show you the code:请允许我向您展示代码:
require 'pg'
@conn = PG::Connection.open(:dbname => 'db_15_11_labs')
@conn.prepare('insert', 'INSERT INTO house (housenumber, street) VALUES ($1, $2) returning id')
@words = ["Foo", "Bar", "Bash", "Bang"]
def populate
100.times.each_with_index do |i|
# cycle through the @words array for street names, use i as house number
ins = @conn.exec_prepared('insert', [i, "#{@words1[i % 4]} street"])
end
end
Basically, the condition is that if the returned id ( ins[0]['id']
) is even, rollback the transaction.基本上,条件是如果返回的 id (
ins[0]['id']
) 是偶数,则回滚事务。 I figure that if ins[0]['id'] % 2 == 0
I need to throw some sort of exception but how do I do that and more importantly, how do I encode that information into the syntax given in the docs ?我认为如果
ins[0]['id'] % 2 == 0
我需要抛出某种异常,但我该怎么做,更重要的是,我如何将该信息编码到文档中给出的语法中?
Thank you for your time.谢谢你的时间。
EDIT 1编辑 1
I have now managed to get the syntax that will allow for the conditions to be placed within the defined transaction as follows:我现在已经设法获得允许将条件放置在定义的事务中的语法,如下所示:
@conn.transaction do |conn|
ins = @conn.exec_prepared('insert', [i, "#{@words1[i % 100]} street"])
end
and so this question really becomes more "how do I throw and catch an exception when ins[0]['id'] % 2 == 0
所以这个问题真的变得更加“当
ins[0]['id'] % 2 == 0
时我如何抛出和捕获异常
I have tried following a couple of simple tutorials on raising exceptions but doing the following:我尝试遵循几个关于引发异常的简单教程,但执行以下操作:
throw :id_exception if (@ins[0]['id'].to_i % 2) == 0
catch :id_exception do
puts "caught :id_exception #{}"
end
inside the transaction results in an 'throw': uncaught throw :id_exception (ArgumentError)
交易内部导致
'throw': uncaught throw :id_exception (ArgumentError)
Transactions rollback automatically if an exception is raised inside the block.如果在块内引发异常,事务会自动回滚。 So you just need to create a little Exception class for yourself, raise one inside the block, and then arrange to rescue it so your program doesn't error-exit due to the raised exception.
所以你只需要为自己创建一个小的 Exception 类,在块内引发一个,然后安排救援它,这样你的程序就不会因为引发的异常而错误退出。
Try something like this:尝试这样的事情:
class MyLittleIdError < StandardError
end
begin
@conn.transaction do |conn|
ins = conn.exec_prepared('insert', [i, "#{@words1[i % 100]} street"])
raise MyLittleIdError if (ins[0]['id'].to_i % 2) == 0
end
rescue MyLittleIdError
puts "aha! we have rolled back."
end
I am currently taking a databases course and one of the lab questions has me stumped as to how to implement the above and indeed, if it was even possible.我目前正在上一门数据库课程,而实验室问题之一让我感到困惑,例如如何实现以上所述,甚至是可能的话。 I have tried searching the docs but the transaction method defined is quite vague.
我尝试搜索文档,但是定义的交易方法相当模糊。
This is the first time I have tried to do any database manipulation WITHOUT the comfort blanket of Rails and so I am a little lost.这是我第一次尝试在没有Rails舒适性的情况下进行任何数据库操作,因此我有些失落。 I have managed to create a connection to my postgresql database and can execute statements, the final thing that I need to do is rollback a transaction based on a simple condition.
我已经设法建立了到我的Postgresql数据库的连接并且可以执行语句,我要做的最后一件事是基于简单条件回滚事务。
Allow me to show you the code:请允许我向您显示代码:
require 'pg'
@conn = PG::Connection.open(:dbname => 'db_15_11_labs')
@conn.prepare('insert', 'INSERT INTO house (housenumber, street) VALUES ($1, $2) returning id')
@words = ["Foo", "Bar", "Bash", "Bang"]
def populate
100.times.each_with_index do |i|
# cycle through the @words array for street names, use i as house number
ins = @conn.exec_prepared('insert', [i, "#{@words1[i % 4]} street"])
end
end
Basically, the condition is that if the returned id ( ins[0]['id']
) is even, rollback the transaction.基本上,条件是如果返回的id(
ins[0]['id']
)为偶数,则回滚该事务。 I figure that if ins[0]['id'] % 2 == 0
I need to throw some sort of exception but how do I do that and more importantly, how do I encode that information into the syntax given in the docs ?我认为如果
ins[0]['id'] % 2 == 0
我需要抛出某种异常,但是我该怎么做,更重要的是,如何将该信息编码为docs中给出的语法?
Thank you for your time.感谢您的时间。
EDIT 1编辑1
I have now managed to get the syntax that will allow for the conditions to be placed within the defined transaction as follows:现在,我设法获得了将条件放入定义的事务中的语法,如下所示:
@conn.transaction do |conn|
ins = @conn.exec_prepared('insert', [i, "#{@words1[i % 100]} street"])
end
and so this question really becomes more "how do I throw and catch an exception when ins[0]['id'] % 2 == 0
所以这个问题实际上变得更加“当
ins[0]['id'] % 2 == 0
时我该如何引发并捕获异常
I have tried following a couple of simple tutorials on raising exceptions but doing the following:我尝试遵循一些有关引发异常的简单教程,但是请执行以下操作:
throw :id_exception if (@ins[0]['id'].to_i % 2) == 0
catch :id_exception do
puts "caught :id_exception #{}"
end
inside the transaction results in an 'throw': uncaught throw :id_exception (ArgumentError)
事务内部导致
'throw': uncaught throw :id_exception (ArgumentError)
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