test: cover OrmEagerLoadingTest and teardown

test/test_orm_eager_loading.rb

@@ -0,0 +1,127 @@
+require 'minitest/autorun'
+require 'prism'
+require 'tmpdir'
+
+class OrmEagerLoadingTest < Minitest::Test
+  def setup
+    @dir = Dir.mktmpdir('prism-eager-store')
+    @store = CountingStore.new(File.join(@dir, 'test.pstore'))
+    @store.create_table(:authors, %w[id name])
+    @store.create_table(:posts, %w[id title author_id])
+    @store.create_table(:bios, %w[id author_id headline])
+
+    author_class = Class.new(Prism::Orm::Model) do
+      table_name :authors
+      has_many :posts, class_name: 'Post', foreign_key: 'author_id'
+      has_one :bio, class_name: 'Bio', foreign_key: 'author_id'
+    end
+    post_class = Class.new(Prism::Orm::Model) do
+      table_name :posts
+      belongs_to :author, class_name: 'Author', foreign_key: 'author_id'
+    end
+    bio_class = Class.new(Prism::Orm::Model) do
+      table_name :bios
+      belongs_to :author, class_name: 'Author', foreign_key: 'author_id'
+    end
+    [author_class, post_class, bio_class].each { |klass| klass.store = @store }
+    Object.const_set(:Author, author_class)
+    Object.const_set(:Post, post_class)
+    Object.const_set(:Bio, bio_class)
+  end
+
+  def teardown
+    FileUtils.remove_entry(@dir)
+    %i[Author Post Bio].each { |name| Object.send(:remove_const, name) if Object.const_defined?(name) }
+  end
+
+  def test_includes_has_many_avoids_n_plus_one_queries
+    3.times do |i|
+      author = Author.create!(name: "author#{i}")
+      2.times { |j| Post.create!(title: "post#{i}-#{j}", author_id: author.id) }
+    end
+
+    @store.reset_query_count!
+    authors = Author.all.includes(:posts).to_a
+    baseline_queries = @store.query_count
+
+    authors.each { |author| author.posts.each(&:title) }
+    assert_equal baseline_queries, @store.query_count,
+      "expected preloaded #posts to be free, but it issued #{@store.query_count - baseline_queries} more queries"
+
+    total_posts = authors.sum { |author| author.posts.size }
+    assert_equal 6, total_posts
+  end
+
+  def test_includes_belongs_to_preloads_single_target
+    author = Author.create!(name: 'solo')
+    Post.create!(title: 'a', author_id: author.id)
+    Post.create!(title: 'b', author_id: author.id)
+
+    @store.reset_query_count!
+    posts = Post.all.includes(:author).to_a
+    baseline = @store.query_count
+    names = posts.map { |post| post.author.name }
+
+    assert_equal baseline, @store.query_count
+    assert_equal %w[solo solo], names
+  end
+
+  def test_includes_has_one_preloads
+    author = Author.create!(name: 'writer')
+    Bio.create!(headline: 'hello there', author_id: author.id)
+
+    loaded = Author.all.includes(:bio).to_a.first
+    assert_equal 'hello there', loaded.bio.headline
+  end
+
+  def test_includes_unknown_association_raises
+    Author.create!(name: 'x')
+    assert_raises(ArgumentError) { Author.all.includes(:nope).to_a }
+  end
+
+  def test_includes_reduces_queries_compared_to_lazy_access
+    3.times do |i|
+      author = Author.create!(name: "author#{i}")
+      2.times { |j| Post.create!(title: "post#{i}-#{j}", author_id: author.id) }
+    end
+
+    @store.reset_query_count!
+    Author.all.to_a.each { |author| author.posts.to_a }
+    lazy_queries = @store.query_count
+
+    @store.reset_query_count!
+    Author.all.includes(:posts).to_a.each { |author| author.posts.to_a }
+    eager_queries = @store.query_count
+
+    assert_equal 4, lazy_queries # 1 authors query + 1 posts query per author (N+1)
+    assert_equal 2, eager_queries # 1 authors query + 1 batched posts query
+    assert_operator eager_queries, :<, lazy_queries
+  end
+end
+
+# Wraps Store#all/#find to count reads, so tests can assert on actual
+# query volume instead of trusting behavior "looks" batched.
+class CountingStore < Prism::Orm::Store
+  def initialize(*)
+    super
+    @query_count = 0
+  end
+
+  def query_count
+    @query_count
+  end
+
+  def reset_query_count!
+    @query_count = 0
+  end
+
+  def all(table)
+    @query_count += 1
+    super
+  end
+
+  def find(table, id)
+    @query_count += 1
+    super
+  end
+end