`ActiveHash::Relation#spawn` passes `conditions` by reference, causing original Relation to be mutated when calling `find_by` multiple times

[ikad]

Bug Summary

When calling find_by multiple times on an ActiveHash::Relation obtained via Course.all, the original Relation's conditions gets mutated, causing subsequent find_by calls to return incorrect results.

Environment

• Ruby: 3.3.4
• Rails: 7.x
• active_hash: 4.0.0

Steps to Reproduce

# ActiveHash model
class Course < ActiveHash::Base
  self.data = [
    { id: 1, name: "Course A" },
    { id: 2, name: "Course B" },
    { id: 3, name: "Course C" }
  ]
end

# Reproduction code
courses = Course.all
courses.conditions  #=> Conditions(@conditions=[])

courses.find_by(id: 1)  #=> #<Course id: 1, name: "Course A"> ✅ Works
courses.conditions  #=> Conditions(@conditions=[Condition(id: 1)]) ← Mutated!

courses.find_by(id: 2)  #=> nil ❌ Should return #<Course id: 2>
courses.conditions  #=> Conditions(@conditions=[Condition(id: 1), Condition(id: 2)])

courses.find_by(id: 1)  #=> nil ❌ Was working before!
courses.all  #=> [] ❌ Empty

Expected Behavior

Calling find_by multiple times should not mutate the original Relation's conditions.

courses = Course.all
courses.find_by(id: 1)  #=> #<Course id: 1>
courses.find_by(id: 2)  #=> #<Course id: 2>
courses.find_by(id: 1)  #=> #<Course id: 1>
courses.conditions  #=> Conditions(@conditions=[]) ← Should remain empty

Analysis

After investigating, it appears that the spawn method in lib/active_hash/relation.rb passes conditions by reference:

def spawn
  self.class.new(klass, all_records, conditions, order_values)
end

find_by internally calls where(options).first, and where calls spawn.where!. Even though spawn creates a new Relation, the conditions (ActiveHash::Relation::Conditions object) still references the same object as the original Relation. When where! calls conditions << Condition.new(...), it also mutates the original Relation's @conditions array.

Current Workaround

In our project, we are using the following monkey patch as a workaround:

# config/initializers/active_hash_patch.rb

module ActiveHashConditionsPatch
  def deep_dup
    self.class.new(conditions.dup)
  end
end

ActiveHash::Relation::Conditions.prepend(ActiveHashConditionsPatch)

module ActiveHashRelationPatch
  def spawn
    self.class.new(klass, all_records, conditions.deep_dup, order_values.dup)
  end
end

ActiveHash::Relation.prepend(ActiveHashRelationPatch)

We have confirmed that this patch resolves the issue and produces the expected behavior.

If this approach seems appropriate, I would be happy to see it incorporated into the gem. However, I'm not deeply familiar with the internal design of this gem, so please let me know if I'm missing something important or if there's a specific reason for the current implementation.