db_mysql.nim is missing sql* proc

[milosn]

I needed to add this to db_mysql.nim to make it work:

proc sql*(query: string): TSqlQuery {.noSideEffect, inline.} =  
  ## constructs a TSqlQuery from the string `query`. This is supposed to be 
  ## used as a raw-string-literal modifier:
  ## ``sql"update user set counter = counter + 1"``
  ##
  ## If assertions are turned off, it does nothing. If assertions are turned 
  ## on, later versions will check the string for valid syntax.
  result = TSqlQuery(query)

[milosn]

Few more fixes:

http://pastie.org/9139705

[Varriount]

What really needs to be done is that the various db modules need to have some sort of common module from which they all import and export. @milosn could you please package your changes as a pull request?

[dom96]

Perhaps, it all depends on how many things are actually shared between these modules. If there are many then we should ask @Araq where to put this common stuff. I guess he will want something like a db_base module.

[milosn]

Another small pacth ... this one helps preserve the representation of DB NULL in Nimrod ... NULL <-> nil:

http://pastie.org/9475268

[milosn]

Just to give some insight ... I made these fixes while trying to write very simple ActiveRecord style ORM for Nimrod.

2 things i needed fixed/decided were: representation of database NULL value in Nimrod (i opted for nil for strings and other values for other types) and representation of SKIP_FIELD (so if you have ActiveRecord object 'o', and on next update you wish to skip updating field/column 'o.my_column' you need a special value that your ORM can recognise and dont generate SQL for that column) ... that sort of looks like this:

const
INT_NULL* = high(int64)
INT_SKIP* = low(int64)

FLOAT_NULL* = +INF
FLOAT_SKIP* = -INF

STRING_NULL* = nil
STRING_SKIP* = "STRING_SKIP"

... and a bit more "magic" which wires it all up. Other projects at work came up with higher priority so this project is currently on hold here.

[dom96]

I think you should use object variants to encode NULL values in Nimrod.

type
  DbValueKind = enum
    DbNull, DbString

  DbValue = object
    case kind: DbValueKind
    of DbNull: nil
    of DbString:
      strval: string
    # etc...

Also, please create PRs for your changes. Otherwise it's unlikely they will be included.

[Araq]

db_common.nim exists now.