From: Brian Candler <b.candler@...>
Date: 2011-01-02T05:10:58+09:00
Subject: Re: write right method to be concise

Pen Ttt wrote in post #971751:
> there is a section of my program,it can run,
>     require 'mysql'
>     dbh = Mysql.real_connect("localhost", "root", "222222")
>     days.times do  #days=10000
>     case  code
>     when  "hk"  then
>         str="use  dzh_hk"
>         dbh.query(str)
>         str_insert="insert into quote (code,date,price)values (?,?,?)
>         st=dbh.prepare(str_insert)
>         st.execute(data[0],data[1],data[2])
>      when  "sh"  then
>         str="use  dzh_sk"
>         dbh.query(str)
>         str_insert="insert into quote (code,date,price)values (?,?,?)
>         st=dbh.prepare(str_insert)
>         st.execute(data[0],data[1],data[2])
>      when  "sz"  then
>         str="use  dzh_sz"
>         dbh.query(str)
>         str_insert="insert into quote (code,date,price)values (?,?,?)
>         st=dbh.prepare(str_insert)
>         st.execute(data[0],data[1],data[2])
>      end
>     end
> #others ommitted
>    i feel it's  burdensome，want to make it be concise, i writ a method
> in my program
>
> p1:
> require 'mysql'
> days.times do
>   def  myinsert(code,data)
>     dbh = Mysql.real_connect("localhost", "root", "222222")
>     str="use  dzh_"+code
>     dbh.query(str)
>     str_insert="insert into quote (code,date,price)values (?,?,?)
>     st=dbh.prepare(str_insert)
>     st.execute(data[0],data[1],data[2])
>   end
> end
> #others ommitted
> Mysql::Error: Too many connections
>
> p2:
> require 'mysql'
> dbh = Mysql.real_connect("localhost", "root", "222222")
> days.times do
>   def  myinsert(code,data)
>     str="use  dzh_"+code
>     dbh.query(str)
>     str_insert="insert into quote (code,date,price)values (?,?,?)
>     st=dbh.prepare(str_insert)
>     st.execute(data[0],data[1],data[2])
>   end
> end
> #others ommitted
> NameError: undefined local variable or method `dbh' for main:Object
>
> would you mind tell me to write a right method to make it be concise?

You have several choices:

1. Pass dbh as an extra parameter to myinsert()

2. Make a wrapper class which holds the handle

class SqlHelper
  def initialize(dbh)
    @dbh = dbh
  end
  def myinsert(code,data)
    @dbh.query("use dhz_#{code}")
    ... etc
  end
end

sql = SqlHelper.new(dbh)
sql.myinsert(code, data)

3. Use a global variable ($dbh) to hold your database handle. This is 
probably OK for a short script, but is poor practice when building a 
large program.

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