adding some roflscale to the sql visitor · rails/arel@e232226

module Arel

module Visitors

class ToSql < Arel::Visitors::Visitor

##

# This is some roflscale crazy stuff. I'm roflscaling this because

# building SQL queries is a hotspot. I will explain the roflscale so that

# others will not rm this code.

#

# In YARV, string literals in a method body will get duped when the byte

# code is executed. Let's take a look:

#

# > puts RubyVM::InstructionSequence.new('def foo; "bar"; end').disasm

#

# == disasm: <RubyVM::InstructionSequence:foo@<compiled>>=====

# 0000 trace 8

# 0002 trace 1

# 0004 putstring "bar"

# 0006 trace 16

# 0008 leave

#

# The `putstring` bytecode will dup the string and push it on the stack.

# In many cases in our SQL visitor, that string is never mutated, so there

# is no need to dup the literal.

#

# If we change to a constant lookup, the string will not be duped, and we

# can reduce the objects in our system:

#

# > puts RubyVM::InstructionSequence.new('BAR = "bar"; def foo; BAR; end').disasm

#

# == disasm: <RubyVM::InstructionSequence:foo@<compiled>>========

# 0000 trace 8

# 0002 trace 1

# 0004 getinlinecache 11, <ic:0>

# 0007 getconstant :BAR

# 0009 setinlinecache <ic:0>

# 0011 trace 16

# 0013 leave

#

# `getconstant` should be a hash lookup, and no object is duped when the

# value of the constant is pushed on the stack. Hence the crazy

# constants below.

WHERE = ' WHERE ' # :nodoc:

SPACE = ' ' # :nodoc:

COMMA = ', ' # :nodoc:

GROUP_BY = ' GROUP BY ' # :nodoc:

WINDOW = ' WINDOW ' # :nodoc:

AND = ' AND ' # :nodoc:

DISTINCT = 'DISTINCT' # :nodoc:

attr_accessor :last_column

def initialize connection

def visit_Arel_Nodes_DeleteStatement o

[

"DELETE FROM #{visit o.relation}",

("WHERE #{o.wheres.map { |x| visit x }.join ' AND '}" unless o.wheres.empty?)

("WHERE #{o.wheres.map { |x| visit x }.join AND}" unless o.wheres.empty?)

].compact.join ' '

end

end

def visit_Arel_Nodes_SelectCore o

[

"SELECT",

(visit(o.top) if o.top),

(visit(o.set_quantifier) if o.set_quantifier),

("#{o.projections.map { |x| visit x }.join ', '}" unless o.projections.empty?),

("FROM #{visit(o.source)}" if o.source && !o.source.empty?),

("WHERE #{o.wheres.map { |x| visit x }.join ' AND ' }" unless o.wheres.empty?),

("GROUP BY #{o.groups.map { |x| visit x }.join ', ' }" unless o.groups.empty?),

(visit(o.having) if o.having),

("WINDOW #{o.windows.map { |x| visit x }.join ', ' }" unless o.windows.empty?)

].compact.join ' '

str = "SELECT"

str << " #{visit(o.top)}" if o.top

str << " #{visit(o.set_quantifier)}" if o.set_quantifier

unless o.projections.empty?

str << SPACE

len = o.projections.length - 1

o.projections.each_with_index do |x, i|

str << visit(x)

str << COMMA unless len == i

end

end

str << " FROM #{visit(o.source)}" if o.source && !o.source.empty?

unless o.wheres.empty?

str << WHERE

len = o.wheres.length - 1

o.wheres.each_with_index do |x, i|

str << visit(x)

str << AND unless len == i

end

end

unless o.groups.empty?

str << GROUP_BY

len = o.groups.length - 1

o.groups.each_with_index do |x, i|

str << visit(x)

str << COMMA unless len == i

end

end

str << " #{visit(o.having)}" if o.having

unless o.windows.empty?

str << WINDOW

len = o.windows.length - 1

o.windows.each_with_index do |x, i|

str << visit(x)

str << COMMA unless len == i

end

end

str

end

def visit_Arel_Nodes_Bin o

visit o.expr

end

def visit_Arel_Nodes_Distinct o

'DISTINCT'

DISTINCT

end

def visit_Arel_Nodes_DistinctOn o