Class: Scryer::PerformanceRules::NPlusOneQueryRule

Inherits:
Rule
  • Object
show all
Defined in:
lib/scryer/performance_rules/n_plus_one_query_rule.rb

Overview

Flags likely N+1 queries: inside a .each/.map block whose receiver looks like an Active Record collection (a local variable previously assigned from Model.where(...)/Model.all/Model.find(...), or a bare instance variable — the common @orders.each do |order| ... end shape), a bare no-arg .method_name call directly on the block variable (likely an association access, e.g. order.line_items) is flagged unless an .includes(:that_name) appeared earlier in the same base query chain.

This is a heuristic, not type inference: it can't tell an association read (order.line_items, which issues a query per row) from a plain attribute/column read (order.status) or a harmless Ruby method call — both parse identically as a bare no-arg call on the block variable. A small block-list of universally-common non-association methods (to_s, present?, class, ...) cuts down the noisiest false positives, but real false positives on attribute reads are still expected and normal for this class of tool (see README).

Constant Summary collapse

QUERY_METHODS = 
%w[where all find find_by find_by! order limit].freeze
LOOP_METHODS = 
%w[each map collect each_with_index].freeze
NON_ASSOCIATION_METHODS =

Bare methods that are overwhelmingly plain Ruby/attribute reads rather than association traversal — flagging these would be mostly noise.

%w[
  to_s to_i to_a to_h inspect class dup clone freeze frozen? hash
  present? blank? nil? empty? any? id id_value == equal? try tap then
  is_a? kind_of? instance_of? respond_to? send public_send object_id
  itself
].freeze

Instance Attribute Summary

Attributes inherited from Rule

#file, #sexp, #source

Instance Method Summary collapse

Methods inherited from Rule

inherited, #initialize

Constructor Details

This class inherits a constructor from Scryer::Rule

Instance Method Details

#scan ⇒ Object 



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# File 'lib/scryer/performance_rules/n_plus_one_query_rule.rb', line 37

def scan
  findings = []

  Ast.each_node(sexp) do |node|
    next unless Ast.tagged?(node, :def, :defs)

    body = node.last
    bindings = query_bindings(body)

    Ast.each_node(body) do |block_call|
      next unless Ast.tagged?(block_call, :method_add_block)

      call_node = block_call[1]
      receiver, loop_method = Ast.call_name(call_node) || [nil, nil]
      next unless LOOP_METHODS.include?(loop_method)
      next unless receiver

      base_name = var_or_ivar_name(receiver)
      next unless base_name

      includes = if bindings.key?(base_name)
                   bindings[base_name]
                 elsif base_name.start_with?("@")
                   [] # ivar set elsewhere — treat as an AR collection with no known eager-loading
                 end
      next unless includes # local var we never saw assigned from a query — don't guess

      block_node = block_call[2]
      param_name = block_param_name(block_node)
      next unless param_name

      findings.concat(association_calls(block_node[2], param_name, includes))
    end
  end

  findings
end