在PL / Python函数之间重用纯Python函数 [英] Reusing pure Python functions between PL/Python functions

问题描述

我想在
两个或多个PL / Python函数之间声明并共享一些简单的纯python函数。我正在使用Postgres 9.3。

I would like to declare and share some simple, pure python functions between two or more PL/Python functions. I am using Postgres 9.3.

例如，我有：

 CREATE OR REPLACE FUNCTION get_mod(modifier varchar)
  RETURNS varchar
    AS $$
      def is_float(val):
        try:
            if val:
               float(val)
               return True
            else:
               return False
        except ValueError:
            return False
      if modifier is None:
        return "NOMOD"
      if is_float(modifier):
        return str(float(modifier)*1)
      return modifier
    $$ LANGUAGE plpythonu;

我想在其中使用函数 is_float 其他一些PL / Python函数。
我知道我可以将其创建为可调用的PL / Python函数，但是我发现它比直接调用纯Python自定义实用程序函数要麻烦得多（执行对PL / Python的基于SQL的调用）。

I would like to use function is_float in some other PL/Python function. I understand I could create it as callable PL/Python function, but I find that much clunkier (to execute SQL-based call to PL/Python) than just making a straight call to a pure Python, custom utility function.

是否可以在Postgres上通过PL / Python可重用的纯Python函数创建和公开？

Is it possible to create and expose through PL/Python reusable pure Python functions on Postgres?

推荐答案

我通常要做的是使用 GD 。缺点是，由于GD是每个会话对象，因此每次启动新会话时都需要加载它。解决此问题的方法是在每个会话开始时运行一个启动功能，该功能填充数据库以供进一步使用。

What I usually do is pass the functions around using GD. The downside is that since GD is a per session object you need to load it each time you start a new session. The way you can approach this is to have a bootstrap function that you run at the beginning of each session that primes the database for further use. Something like:

create or replace function bootstrap() returns void
as
$$
def is_float(val):
  # did some simplifying here, 
  try:   
    float(val) # Take notice that booleans will convert to float successfully
    return True
  except (ValueError, TypeError):
    return False

GD['is_float'] = is_float
$$ language plpythonu;

现在您可以修改原始功能：

Now you can modify your original function:

CREATE OR REPLACE FUNCTION get_mod(modifier varchar)
 RETURNS varchar
    AS $$
      # Optionally run bootstrap() here
      plpy.execute("select bootstrap()")
      ###
      if modifier is None:
        return "NOMOD"
      if GD['is_float'](modifier):
        return str(float(modifier)*1)
      return modifier
    $$ LANGUAGE plpythonu;

要执行此操作，您必须运行 select bootstrap（ ）; 在每个会话的开始，或者作为流程的一部分正在调用的第一个函数的一部分……或者实际上是您原始函数的一部分。

In order for this to work you'd have to run select bootstrap(); at the start of each session, or as part of the first function you are calling as part of the flow... Or indeed as part of your original function.

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