Bulk Insert: Reuse indexes for unique_by

I found `:unique_by` with `:columns` and `:where` inside it tough to
grasp. The documentation only mentioned indexes and partial indexes.
So why duplicate a model's indexes in an insert_all/upsert_all call
when we can just look it up?

This has the added benefit of raising if no index is found, such that
people can't insert thousands of records without relying on an index
of some form.

3 files changed, 88 insertions, 64 deletions

diff --git a/activerecord/lib/active_record/insert_all.rb b/activerecord/lib/active_record/insert_all.rb
index 98c98d61cd..d30aee7c00 100644
--- a/activerecord/lib/active_record/insert_all.rb
+++ b/activerecord/lib/active_record/insert_all.rb
@@ -14,6 +14,7 @@ module ActiveRecord
       @returning = (connection.supports_insert_returning? ? primary_keys : false) if @returning.nil?
       @returning = false if @returning == []
 
+      @unique_by = find_unique_index_for(unique_by) if unique_by
       @on_duplicate = :skip if @on_duplicate == :update && updatable_columns.empty?
 
       ensure_valid_options_for_connection!
@@ -27,6 +28,11 @@ module ActiveRecord
       keys - readonly_columns - unique_by_columns
     end
 
+    def primary_keys
+      Array(model.primary_key)
+    end
+
+
     def skip_duplicates?
       on_duplicate == :skip
     end
@@ -47,6 +53,21 @@ module ActiveRecord
     end
 
     private
+      def find_unique_index_for(unique_by)
+        match = Array(unique_by).map(&:to_s)
+
+        if index = unique_indexes.find { |i| match.include?(i.name) || i.columns == match }
+          index
+        else
+          raise ArgumentError, "No unique index found for #{unique_by}"
+        end
+      end
+
+      def unique_indexes
+        connection.schema_cache.indexes(model.table_name).select(&:unique)
+      end
+
+
       def ensure_valid_options_for_connection!
         if returning && !connection.supports_insert_returning?
           raise ArgumentError, "#{connection.class} does not support :returning"
@@ -69,21 +90,20 @@ module ActiveRecord
         end
       end
 
+
       def to_sql
         connection.build_insert_sql(ActiveRecord::InsertAll::Builder.new(self))
       end
 
+
       def readonly_columns
         primary_keys + model.readonly_attributes.to_a
       end
 
       def unique_by_columns
-        unique_by ? unique_by.fetch(:columns).map(&:to_s) : []
+        Array(unique_by&.columns)
       end
 
-      def primary_keys
-        Array.wrap(model.primary_key)
-      end
 
       def verify_attributes(attributes)
         if keys != attributes.keys.to_set
@@ -121,10 +141,13 @@ module ActiveRecord
         end
 
         def conflict_target
-          return unless conflict_columns
-          sql = +"(#{quote_columns(conflict_columns).join(',')})"
-          sql << " WHERE #{where}" if where
-          sql
+          if index = insert_all.unique_by
+            sql = +"(#{quote_columns(index.columns).join(',')})"
+            sql << " WHERE #{index.where}" if index.where
+            sql
+          elsif update_duplicates?
+            "(#{quote_columns(insert_all.primary_keys).join(',')})"
+          end
         end
 
         def updatable_columns
@@ -150,18 +173,6 @@ module ActiveRecord
           def quote_columns(columns)
             columns.map(&connection.method(:quote_column_name))
           end
-
-          def conflict_columns
-            @conflict_columns ||= begin
-              conflict_columns = insert_all.unique_by.fetch(:columns) if insert_all.unique_by
-              conflict_columns ||= Array.wrap(model.primary_key) if update_duplicates?
-              conflict_columns
-            end
-          end
-
-          def where
-            insert_all.unique_by && insert_all.unique_by[:where]
-          end
       end
   end
 end
diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index 0c31f0f57e..8b7c9f59fa 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -92,25 +92,21 @@ module ActiveRecord
       #   <tt>returning: %w[ id name ]</tt> to return the id and name of every successfully inserted
       #   record or pass <tt>returning: false</tt> to omit the clause.
       #
-      # [:unique_by]
-      #   (Postgres and SQLite only) In a table with more than one unique constraint or index,
+      # [:unique_index]
+      #   (Postgres and SQLite only) In a table with more than one unique constaint or index,
       #   new records may be considered duplicates according to different criteria. By default,
-      #   new rows will be skipped if they violate _any_ unique constraint or index. By defining
-      #   <tt>:unique_by</tt>, you can skip rows that would create duplicates according to the given
+      #   new rows will be skipped if they violate _any_ unique constraint/index. By passing
+      #   <tt>:unique_index</tt>, you can skip rows that would create duplicates according to the given
       #   constraint but raise <tt>ActiveRecord::RecordNotUnique</tt> if rows violate other constraints.
       #
-      #   (For example, maybe you assume a client will try to import the same ISBNs more than
+      #   For example, maybe you assume a client will try to import the same ISBNs more than
       #   once and want to silently ignore the duplicate records, but you don't except any of
       #   your code to attempt to create two rows with the same primary key and would appreciate
-      #   an exception report in that scenario.)
+      #   an exception instead.
       #
-      #   Indexes can be identified by an array of columns:
+      #   Indexes can be identified by name:
       #
-      #     unique_by: { columns: %w[ isbn ] }
-      #
-      #   Partial indexes can be identified by an array of columns and a <tt>:where</tt> condition:
-      #
-      #     unique_by: { columns: %w[ isbn ], where: "published_on IS NOT NULL" }
+      #     unique_index: :isbn
       #
       # ==== Example
       #
@@ -120,7 +116,6 @@ module ActiveRecord
       #     { id: 1, title: 'Rework', author: 'David' },
       #     { id: 1, title: 'Eloquent Ruby', author: 'Russ' }
       #   ])
-      #
       def insert_all(attributes, returning: nil, unique_by: nil)
         InsertAll.new(self, attributes, on_duplicate: :skip, returning: returning, unique_by: unique_by).execute
       end
@@ -174,12 +169,11 @@ module ActiveRecord
       #   ])
       #
       #   # Raises ActiveRecord::RecordNotUnique because 'Eloquent Ruby'
-      #   # does not have a unique ID
+      #   # does not have a unique id.
       #   Book.insert_all!([
       #     { id: 1, title: 'Rework', author: 'David' },
       #     { id: 1, title: 'Eloquent Ruby', author: 'Russ' }
       #   ])
-      #
       def insert_all!(attributes, returning: nil)
         InsertAll.new(self, attributes, on_duplicate: :raise, returning: returning).execute
       end
@@ -217,43 +211,32 @@ module ActiveRecord
       #   <tt>returning: %w[ id name ]</tt> to return the id and name of every successfully inserted
       #   record or pass <tt>returning: false</tt> to omit the clause.
       #
-      # [:unique_by]
-      #   (Postgres and SQLite only) In a table with more than one unique constraint or index,
+      # [:unique_index]
+      #   (Postgres and SQLite only) In a table with more than one unique constaint or index,
       #   new records may be considered duplicates according to different criteria. For MySQL,
       #   an upsert will take place if a new record violates _any_ unique constraint. For
       #   Postgres and SQLite, new rows will replace existing rows when the new row has the
-      #   same primary key as the existing row. In case of SQLite, an upsert operation causes
-      #   an insert to behave as an update or a no-op if the insert would violate
-      #   a uniqueness constraint. By defining <tt>:unique_by</tt>, you can supply
-      #   a different unique constraint for matching new records to existing ones than the
-      #   primary key.
-      #
-      #   (For example, if you have a unique index on the ISBN column and use that as
-      #   the <tt>:unique_by</tt>, a new record with the same ISBN as an existing record
-      #   will replace the existing record but a new record with the same primary key
-      #   as an existing record will raise <tt>ActiveRecord::RecordNotUnique</tt>.)
-      #
-      #   Indexes can be identified by an array of columns:
+      #   same primary key as the existing row. By passing <tt>:unique_index</tt>, you can supply
+      #   a different index than the primary key one to match new records to existing ones.
       #
-      #     unique_by: { columns: %w[ isbn ] }
+      #   For example, if you have a unique index on the ISBN column and pass that as
+      #   <tt>:unique_index</tt>, a new record with the same ISBN as an existing record
+      #   will replace the existing record but a new record with the same primary key
+      #   as an existing record will raise <tt>ActiveRecord::RecordNotUnique</tt>.
       #
-      #   Partial indexes can be identified by an array of columns and a <tt>:where</tt> condition:
+      #   Indexes can be identified by name:
       #
-      #     unique_by: { columns: %w[ isbn ], where: "published_on IS NOT NULL" }
+      #     unique_index: :isbn
       #
       # ==== Examples
       #
-      #   # Given a unique index on <tt>books.isbn</tt> and the following record:
-      #   Book.create!(title: 'Rework', author: 'David', isbn: '1')
+      #   # Insert multiple records, performing an upsert when records have duplicate ISBNs.
+      #   # Here 'Eloquent Ruby' will overwrite 'Rework' because its ISBN is duplicate.
       #
-      #   # Insert multiple records, allowing new records with the same ISBN
-      #   # as an existing record to overwrite the existing record.
-      #   # ('Eloquent Ruby' will overwrite 'Rework' because its ISBN is duplicate)
       #   Book.upsert_all([
-      #     { title: 'Eloquent Ruby', author: 'Russ', isbn: '1' },
-      #     { title: 'Clean Code', author: 'Robert', isbn: '2' }
-      #   ], unique_by: { columns: %w[ isbn ] })
-      #
+      #     { title: 'Rework', author: 'David', isbn: '1' },
+      #     { title: 'Eloquent Ruby', author: 'Russ', isbn: '1' }
+      #   ], unique_index: :isbn)
       def upsert_all(attributes, returning: nil, unique_by: nil)
         InsertAll.new(self, attributes, on_duplicate: :update, returning: returning, unique_by: unique_by).execute
       end
diff --git a/activerecord/test/cases/insert_all_test.rb b/activerecord/test/cases/insert_all_test.rb
index a3e920969d..0818d7c1ab 100644
--- a/activerecord/test/cases/insert_all_test.rb
+++ b/activerecord/test/cases/insert_all_test.rb
@@ -95,7 +95,37 @@ class InsertAllTest < ActiveRecord::TestCase
 
     assert_raise ActiveRecord::RecordNotUnique do
       Book.insert_all [{ id: 1, name: "Agile Web Development with Rails" }],
-        unique_by: { columns: %i{author_id name} }
+        unique_by: :index_books_on_author_id_and_name
+    end
+  end
+
+  def test_insert_all_and_upsert_all_with_index_finding_options
+    skip unless supports_insert_conflict_target?
+
+    assert_difference "Book.count", +3 do
+      Book.insert_all [{ name: "Rework", author_id: 1 }], unique_by: :isbn
+      Book.insert_all [{ name: "Remote", author_id: 1 }], unique_by: %i( author_id name )
+      Book.insert_all [{ name: "Renote", author_id: 1 }], unique_by: :index_books_on_isbn
+    end
+
+    assert_raise ActiveRecord::RecordNotUnique do
+      Book.upsert_all [{ name: "Rework", author_id: 1 }], unique_by: :isbn
+    end
+  end
+
+  def test_insert_all_and_upsert_all_raises_when_index_is_missing
+    skip unless supports_insert_conflict_target?
+
+    [ :cats, %i( author_id isbn ), :author_id ].each do |missing_or_non_unique_by|
+      error = assert_raises ArgumentError do
+        Book.insert_all [{ name: "Rework", author_id: 1 }], unique_by: missing_or_non_unique_by
+      end
+      assert_match "No unique index", error.message
+
+      error = assert_raises ArgumentError do
+        Book.upsert_all [{ name: "Rework", author_id: 1 }], unique_by: missing_or_non_unique_by
+      end
+      assert_match "No unique index", error.message
     end
   end
 
@@ -120,7 +150,7 @@ class InsertAllTest < ActiveRecord::TestCase
 
     Book.upsert_all [{ id: 101, name: "Perelandra", author_id: 7 }]
     Book.upsert_all [{ id: 103, name: "Perelandra", author_id: 7, isbn: "1974522598" }],
-      unique_by: { columns: %i{author_id name} }
+      unique_by: :index_books_on_author_id_and_name
 
     book = Book.find_by(name: "Perelandra")
     assert_equal 101, book.id, "Should not have updated the ID"
@@ -132,7 +162,7 @@ class InsertAllTest < ActiveRecord::TestCase
 
     Book.upsert_all [{ name: "Out of the Silent Planet", author_id: 7, isbn: "1974522598", published_on: Date.new(1938, 4, 1) }]
     Book.upsert_all [{ name: "Perelandra", author_id: 7, isbn: "1974522598" }],
-      unique_by: { columns: %w[ isbn ], where: "published_on IS NOT NULL" }
+      unique_by: :index_books_on_isbn
 
     assert_equal ["Out of the Silent Planet", "Perelandra"], Book.where(isbn: "1974522598").order(:name).pluck(:name)
   end