Class: Squeel::Visitors::AttributeVisitor

Inherits:
Base
  • Object
show all
Defined in:
lib/squeel/visitors/attribute_visitor.rb

Overview

A visitor that tries to convert visited nodes into Arel::Attributes or other nodes that can be used for grouping, ordering, and the like.

Constant Summary

Constants inherited from Base

Base::DISPATCH

Instance Attribute Summary

Attributes inherited from Base

#context

Instance Method Summary collapse

Methods inherited from Base

#accept, #can_accept?, can_accept?, #initialize, #quote, #quoted?, #visit

Constructor Details

This class inherits a constructor from Squeel::Visitors::Base

Instance Method Details

#implies_context_change?(v) ⇒ Boolean (private)

Returns Whether the given value implies a context change.

Parameters:

  • v —

    The value to consider

Returns:

  • (Boolean) —

    Whether the given value implies a context change



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# File 'lib/squeel/visitors/attribute_visitor.rb', line 29

def implies_context_change?(v)
  can_accept?(v)
end

#visit_Array(o, parent) ⇒ Array (private)

Visit elements of an array that it’s possible to visit – leave other elements untouched.

Parameters:

  • o (Array) —

    The array to visit

  • parent —

    The array’s parent within the context

Returns:

  • (Array) —

    The flattened array with elements visited



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# File 'lib/squeel/visitors/attribute_visitor.rb', line 74

def visit_Array(o, parent)
  o.map { |v| can_accept?(v) ? accept(v, parent) : v }.flatten
end

#visit_Hash(o, parent) ⇒ Array (private)

Visit a Hash. This entails iterating through each key and value and visiting each value in turn.

Parameters:

  • o (Hash) —

    The Hash to visit

  • parent —

    The current parent object in the context

Returns:

  • (Array) —

    An array of values for use in an ordering, grouping, etc.



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# File 'lib/squeel/visitors/attribute_visitor.rb', line 17

def visit_Hash(o, parent)
  o.map do |k, v|
    if implies_context_change?(v)
      visit_with_context_change(k, v, parent)
    else
      visit_without_context_change(k, v, parent)
    end
  end.flatten
end

#visit_Squeel_Nodes_Function(o, parent) ⇒ Object (private)

Visit a Function node. Each function argument will be accepted or contextualized if appropriate. Keep in mind that this occurs with the current parent within the context.

Examples:

A function as the endpoint of a keypath

Person.joins{children}.order{children.coalesce(name, '<no name>')}
# => SELECT "people".* FROM "people"
       INNER JOIN "people" "children_people"
         ON "children_people"."parent_id" = "people"."id"
       ORDER BY coalesce("children_people"."name", '<no name>')

Parameters:

  • o (Nodes::Function) —

    The function node to visit

  • parent —

    The node’s parent within the context



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# File 'lib/squeel/visitors/attribute_visitor.rb', line 133

def visit_Squeel_Nodes_Function(o, parent)
  args = o.args.map do |arg|
    case arg
    when Nodes::Function, Nodes::KeyPath
      accept(arg, parent)
    when Symbol, Nodes::Stub
      Arel.sql(arel_visitor.accept contextualize(parent)[arg.to_sym])
    else
      quote arg
    end
  end
  Arel::Nodes::NamedFunction.new(o.name, args, o.alias)
end

#visit_Squeel_Nodes_KeyPath(o, parent) ⇒ Object (private)

Visit a keypath. This will traverse the keypath’s “path”, setting a new parent as though the keypath’s endpoint was in a deeply-nested hash, then visit the endpoint with the new parent.

Parameters:

  • o (Nodes::KeyPath) —

    The keypath to visit

  • parent —

    The keypath’s parent within the context

Returns:

  • The visited endpoint, with the parent from the KeyPath’s path.



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# File 'lib/squeel/visitors/attribute_visitor.rb', line 105

def visit_Squeel_Nodes_KeyPath(o, parent)
  parent = traverse(o, parent)

  accept(o.endpoint, parent)
end

#visit_Squeel_Nodes_Operation(o, parent) ⇒ Object (private)

Visit an Operation node. Each operand will be accepted or contextualized if appropriate. Keep in mind that this occurs with the current parent within the context.

Parameters:

  • o (Nodes::Operation) —

    The operation node to visit

  • parent —

    The node’s parent within the context



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# File 'lib/squeel/visitors/attribute_visitor.rb', line 153

def visit_Squeel_Nodes_Operation(o, parent)
  args = o.args.map do |arg|
    case arg
    when Nodes::Function
      accept(arg, parent)
    when Symbol, Nodes::Stub
      Arel.sql(arel_visitor.accept contextualize(parent)[arg.to_sym])
    else
      quote arg
    end
  end

  op = case o.operator
  when :+
    Arel::Nodes::Addition.new(args[0], args[1])
  when :-
    Arel::Nodes::Subtraction.new(args[0], args[1])
  when :*
    Arel::Nodes::Multiplication.new(args[0], args[1])
  when :/
    Arel::Nodes::Division.new(args[0], args[1])
  else
    Arel.sql("#{arel_visitor.accept(args[0])} #{o.operator} #{arel_visitor.accept(args[1])}")
  end
  o.alias ? op.as(o.alias) : op
end

#visit_Squeel_Nodes_Order(o, parent) ⇒ Arel::Nodes::Ordering (private)

Visit an Order node.

Parameters:

  • o (Nodes::Order) —

    The order node to visit

  • parent —

    The node’s parent within the context

Returns:

  • (Arel::Nodes::Ordering) —

    An ascending or desending ordering



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# File 'lib/squeel/visitors/attribute_visitor.rb', line 116

def visit_Squeel_Nodes_Order(o, parent)
  accept(o.expr, parent).send(o.descending? ? :desc : :asc)
end

#visit_Squeel_Nodes_Stub(o, parent) ⇒ Arel::Attribute (private)

Visit a stub. This will return an attribute named after the stub against the current parent’s contextualized table.

Parameters:

  • o (Nodes::Stub) —

    The stub to visit

  • parent —

    The stub’s parent within the context

Returns:

  • (Arel::Attribute) —

    An attribute on the contextualized parent table



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# File 'lib/squeel/visitors/attribute_visitor.rb', line 94

def visit_Squeel_Nodes_Stub(o, parent)
  contextualize(parent)[o.symbol]
end

#visit_Symbol(o, parent) ⇒ Arel::Attribute (private)

Visit a symbol. This will return an attribute named after the symbol against the current parent’s contextualized table.

Parameters:

  • o (Symbol) —

    The symbol to visit

  • parent —

    The symbol’s parent within the context

Returns:

  • (Arel::Attribute) —

    An attribute on the contextualized parent table



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# File 'lib/squeel/visitors/attribute_visitor.rb', line 84

def visit_Symbol(o, parent)
  contextualize(parent)[o]
end

#visit_with_context_change(k, v, parent) ⇒ Object (private)

Change context (by setting the new parent to the result of a #find or #traverse on the key), then accept the given value.

Parameters:

  • k —

    The hash key

  • v —

    The hash value

  • parent —

    The current parent object in the context

Returns:

  • The visited value



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# File 'lib/squeel/visitors/attribute_visitor.rb', line 40

def visit_with_context_change(k, v, parent)
  parent = case k
    when Nodes::KeyPath
      traverse(k, parent, true)
    else
      find(k, parent)
    end

  if Array === v
    v.map {|val| accept(val, parent || k)}
  else
    can_accept?(v) ? accept(v, parent || k) : v
  end
end

#visit_without_context_change(k, v, parent) ⇒ Object (private)

If there is no context change, we’ll just return the value unchanged, currently. Is this really the right behavior? I don’t think so, but it works in this case.

Parameters:

  • k —

    The hash key

  • v —

    The hash value

  • parent —

    The current parent object in the context

Returns:

  • The same value we just received. Yeah, this method’s pretty pointless, for now, and only here for consistency’s sake.



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# File 'lib/squeel/visitors/attribute_visitor.rb', line 64

def visit_without_context_change(k, v, parent)
  v
end