Simple DB-like tables in pure Lua with validation

[Lorenzo Donati <lorenzodonatibz@...>]

Hi list!

I'm currently using Lua to store small amounts of record-like data in 
Lua files, using a syntax similar to the following:

-- file table1.lua
Record('field1', 'field2', 1231)
Record('field1', 'field2', 1231)
...

or this one:

-- file table2.lua

Record{ id = 3232, name = 'foo', date = '2010-12-25' }
Record{ id = 1232, name = 'bar', date = '2010-12-31' }
...


Then, after suitably defining the function 'Record', I load those files 
using 'dofile' and process the data in different ways.

Currently I use ad-hoc functions to perform validation on the data, but 
this is becoming unwieldy, since I find this kind of storage very useful 
and flexible and I keep creating these small files (say max 1000 records 
with max 10-20 fields each) for various purposes, and the ad-hoc 
validation functions are becoming the main maintenance hassle.
Sometimes the task gets even more complicated when a field is actually a 
Lua table itself, so the validation routine must recurse into it.

Is there any _very lightweight_ Lua library (pure Lua possibly) which 
could help me in this respect, ie. defining a sort of a pseudo-DB schema 
in a clean way and then use it to validate tables?

I'd like to write something declarative like:

local scheme = NewScheme {
  -- fields description
  id = {
    type = 'number',
    validator = function(field) ... end -- returns true when 'id' is ok
  },
 name = {
    type = 'string',
    validator = function(field) ... end
  }
-- etc.
}

and then in the 'Record' function:

if not scheme:validate(record)	
  then error(...) end


I'd really like to avoid using a true RDBMS, even simple as sqlite, 
since I love the format of the Lua 'data files' (and the advantages they 
provide) and most of the time I don't need to update the data in the 
tables: I only add records at the end manually or with simple append 
procedures from other scripts (even non-Lua).

Any pointer or suggestion are welcome as long as it allows me to retain 
the data files format and it is lightweight (not necessarily a library, 
even a different approach at table data validation, if there is some 
neat Lua trick that can improve readability and maintenance!).

Thanks in advance!

--
Lorenzo