Fixes CollectionAssociation#ids_reader returning incorrect ids for new records

3 files changed, 34 insertions, 1 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 29d218277f..cc1a66c098 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,5 +1,11 @@
 ## unreleased ##
 
+*   Prevent query with NULL foreign key value on CollectionAssociation#ids_reader
+    for non-persisted records. Fixes bug where Company.new.contract_ids would
+    incorrectly load all non-associated Contracts.
+
+    *Jared Armstrong*
+
 *   Fix the `:primary_key` option for `has_many` associations.
     Fixes #10693.
 
diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index 65e882867e..baddb9852f 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -43,7 +43,7 @@ module ActiveRecord
 
       # Implements the ids reader method, e.g. foo.item_ids for Foo.has_many :items
       def ids_reader
-        if loaded? || options[:finder_sql]
+        if owner.new_record? || loaded? || options[:finder_sql]
           load_target.map do |record|
             record.send(reflection.association_primary_key)
           end
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index a75d064ac0..55b57bc2f2 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -1311,6 +1311,33 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert !company.clients.loaded?
   end
 
+  def test_get_ids_for_association_on_new_record_does_not_try_to_find_records
+    Company.columns  # Load schema information so we don't query below
+    Contract.columns # if running just this test.
+
+    company = Company.new
+    assert_queries(0) do
+      company.contract_ids
+    end
+
+    assert_equal [], company.contract_ids
+  end
+
+  def test_set_ids_for_association_on_new_record_applies_association_correctly
+    contract_a = Contract.create!
+    contract_b = Contract.create!
+    another_contract = Contract.create!
+    company = Company.new(:name => "Some Company")
+
+    company.contract_ids = [contract_a.id, contract_b.id]
+    assert_equal [contract_a.id, contract_b.id], company.contract_ids
+    assert_equal [contract_a, contract_b], company.contracts
+
+    company.save!
+    assert_equal company, contract_a.reload.company
+    assert_equal company, contract_b.reload.company
+  end
+
   def test_get_ids_ignores_include_option
     assert_equal [readers(:michael_welcome).id], posts(:welcome).readers_with_person_ids
   end