I've made this abstract class other classes can implement to make themselves storable in a MPTT database scheme without having knowledge of the left/right juggling. In the new entry part of class, I need to be able to insert an arbitrary length hash (@attrs) into the database (using DBI). I can generate the SQL for N values, but when it comes to executing it the SQL DBI's execute() method will not expand an array to fill the arguments it is expecting.

I tried this first:

Code:

cursor = @dbd.prepare(
      "INSERT INTO #{ @table } (#{ @columns['left'] }, #{ @columns['right'] }, #{ @attrs.keys.join(', ') })
         VALUES (?, ?#{ ', ?' * @attrs.length })")
   
      cursor.execute(l, l + 1, @attrs.values)

But execute() fails for @attrs.length > 1

This works, but it's very hawkish:

Code:

exec_attrs = @attrs.keys.collect { |k| "@attrs['#{ k }']" }
   eval "cursor.execute(l, l + 1, #{ exec_attrs.join(', ') })"

So, any better way to do it? Aside from rewriting execute() to handle arrays the way I want, which I may end up doing.

I still don't have a general solution for this but there's a mechanism in DBI that fixes this instance:

Instead of

Code:

cursor.execute(l, l + 1, @attrs.values)

You can do

Code:

cursor.bind_param(1, l)
cursor.bind_param(2, l + 1)
@attrs.each_with_index { |at, idx|
    cursor.bind_param(idx + 3, at[1])
}

Much better.

ralph l mayo, thanks for reply
code you pasted work fine