class Sequel::Unbinder

Unbinder is used to take a dataset filter and return a modified version that unbinds already bound values and returns a dataset with bound value placeholders and a hash of bind values. You can then prepare the dataset and use the bound variables to execute it with the same values.

This class only does a limited form of unbinding where the variable names and values can be associated unambiguously. The only cases it handles are <tt>SQL::ComplexExpression<tt> with an operator in UNBIND_OPS, a first argument that's an instance of a member of UNBIND_KEY_CLASSES, and a second argument that's an instance of a member of UNBIND_VALUE_CLASSES.

So it can handle cases like:

DB.filter(:a=>1).exclude(:b=>2).where{c > 3}

But it cannot handle cases like:

DB.filter(:a + 1 < 0)

Constants

UNBIND_KEY_CLASSES

The key classes (first argument of the ComplexExpression) that will considered for transformation.

UNBIND_OPS

The <tt>SQL::ComplexExpression<tt> operates that will be considered for transformation.

UNBIND_VALUE_CLASSES

The value classes (second argument of the ComplexExpression) that will be considered for transformation.

Attributes

binds[R]

The hash of bind variables that were extracted from the dataset filter.

Public Class Methods

new() click to toggle source

Intialize an empty binds hash.

# File lib/sequel/ast_transformer.rb, line 154
def initialize
  @binds = {}
end

Private Instance Methods

bind_key(obj) click to toggle source

Create a suitable bound variable key for the object, which should be an instance of one of the UNBIND_KEY_CLASSES.

# File lib/sequel/ast_transformer.rb, line 162
def bind_key(obj)
  case obj
  when Symbol
    obj
  when String
    obj.to_sym
  when SQL::Identifier
    bind_key(obj.value)
  when SQL::QualifiedIdentifier
    :"#{bind_key(obj.table)}.#{bind_key(obj.column)}"
  else
    raise Error, "unhandled object in Sequel::Unbinder#bind_key: #{obj}"
  end
end
v(o) click to toggle source

Handle SQL::ComplexExpression instances with suitable ops and arguments, substituting the value with a bound variable placeholder and assigning it an entry in the binds hash with a matching key.

Calls superclass method Sequel::ASTTransformer#v
# File lib/sequel/ast_transformer.rb, line 180
def v(o)
  if o.is_a?(SQL::ComplexExpression) && UNBIND_OPS.include?(o.op)
    l, r = o.args
    l = l.value if l.is_a?(Sequel::SQL::Wrapper)
    r = r.value if r.is_a?(Sequel::SQL::Wrapper)
    if UNBIND_KEY_CLASSES.any?{|c| l.is_a?(c)} && UNBIND_VALUE_CLASSES.any?{|c| r.is_a?(c)} && !r.is_a?(LiteralString)
      key = bind_key(l)
      if (old = binds[key]) && old != r
        raise UnbindDuplicate, "two different values for #{key.inspect}: #{[r, old].inspect}" 
      end
      binds[key] = r
      SQL::ComplexExpression.new(o.op, l, :"$#{key}")
    else
      super
    end
  else
    super
  end
end