Migrate Picture content from BinaryBlobs to Pictures table

db/migrate/20180111162442_move_pictures_blobs_to_pictures.rb

@@ -0,0 +1,52 @@
+class MovePicturesBlobsToPictures < ActiveRecord::Migration[5.0]
+  class BinaryBlob < ActiveRecord::Base
+    include ActiveRecord::IdRegions
+    has_many :binary_blob_parts, -> { order(:id) }, :dependent => :delete_all, :class_name => "MovePicturesBlobsToPictures::BinaryBlobPart"
+    def data
+      binary_blob_parts.pluck(:data).join
+    end
+  end
+  class BinaryBlobPart < ActiveRecord::Base; end
+  class Picture < ActiveRecord::Base
+    include ActiveRecord::IdRegions
+  end
+
+  def up
+    add_column :pictures, :content, :binary
+    add_column :pictures, :extension, :string
+    add_column :pictures, :md5, :string
+
+    say_with_time("Moving picture content from BinaryBlobs to the pictures table") do
+      BinaryBlob.in_my_region.includes(:binary_blob_parts).where(:resource_type => "Picture").find_each do |blob|
+        Picture.update(blob.resource_id, :content => blob.data, :extension => blob.data_type, :md5 => blob.md5)
+        blob.destroy
+      end
+    end
+  end
+
+  def down
+    say_with_time("Moving picture content from the pictures table to BinaryBlobs") do
+      Picture.in_my_region.find_each do |picture|
+        size = picture.content.try(:length).to_i
+        next if size.zero?
+
+        BinaryBlob.create!(
+          :data_type     => picture.extension,
+          :md5           => picture.md5,
+          :part_size     => size,
+          :resource_id   => picture.id,
+          :resource_type => "Picture",
+          :size          => size,
+        ).binary_blob_parts.create!(
+          :data => picture.content,
+          :md5  => picture.md5,
+          :size => size,
+        )
+      end
+    end
+
+    remove_column :pictures, :content
+    remove_column :pictures, :extension
+    remove_column :pictures, :md5
+  end
+end

spec/migrations/20180111162442_move_pictures_blobs_to_pictures_spec.rb

@@ -0,0 +1,106 @@
+require_migration
+
+describe MovePicturesBlobsToPictures do
+  let(:binary_blob_stub)      { migration_stub :BinaryBlob }
+  let(:binary_blob_part_stub) { migration_stub :BinaryBlobPart }
+  let(:picture_stub)          { migration_stub :Picture }
+
+  migration_context :up do
+    it 'Moves a single-part image blob' do
+      picture = picture_stub.create!
+      blob    = binary_blob_stub.create!(
+        :data_type     => "png",
+        :md5           => "ce114e4501d2f4e2dcea3e17b546f339",
+        :part_size     => 1.megabyte,
+        :resource_id   => picture.id,
+        :resource_type => "Picture",
+        :size          => 14,
+      )
+      binary_blob_part_stub.create!(
+        :binary_blob_id => blob.id,
+        :data           => "This is a test",
+        :md5            => "ce114e4501d2f4e2dcea3e17b546f339",
+        :size           => 14,
+      )
+
+      migrate
+
+      expect(picture.reload).to have_attributes(
+        :content   => "This is a test",
+        :extension => "png",
+        :md5       => "ce114e4501d2f4e2dcea3e17b546f339",
+      )
+      expect(binary_blob_stub.count).to eq(0)
+      expect(binary_blob_part_stub.count).to eq(0)
+    end
+
+    it 'Moves a multi-part image blob' do
+      picture = picture_stub.create!
+      blob    = binary_blob_stub.create!(
+        :data_type     => "png",
+        :md5           => "c65dfd70c813cc2d519fcad28ebaee6f",
+        :part_size     => 1.megabyte,
+        :resource_id   => picture.id,
+        :resource_type => "Picture",
+        :size          => 32,
+      )
+      binary_blob_part_stub.create!(
+        :binary_blob_id => blob.id,
+        :data           => "This is a multi",
+        :md5            => "94efec8abb26d346812c3a0a8dc98306",
+        :size           => 15,
+      )
+      binary_blob_part_stub.create!(
+        :binary_blob_id => blob.id,
+        :data           => "-part test stri",
+        :md5            => "10b11598b01f3b02d767e238be22e78b",
+        :size           => 15,
+      )
+      binary_blob_part_stub.create!(
+        :binary_blob_id => blob.id,
+        :data           => "ng",
+        :md5            => "66e10e9ff65ef479654dde3968d3440d",
+        :size           => 2,
+      )
+
+      migrate
+
+      expect(picture.reload).to have_attributes(
+        :content   => "This is a multi-part test string",
+        :extension => "png",
+        :md5       => "c65dfd70c813cc2d519fcad28ebaee6f",
+      )
+      expect(binary_blob_stub.count).to eq(0)
+      expect(binary_blob_part_stub.count).to eq(0)
+    end
+  end
+
+  migration_context :down do
+    it 'Moves back to a single binary blob' do
+      picture = picture_stub.create!(
+        :content   => "This is a test",
+        :extension => "png",
+        :md5       => "ce114e4501d2f4e2dcea3e17b546f339",
+      )
+
+      migrate
+
+      expect(binary_blob_stub.count).to eq(1)
+      expect(binary_blob_part_stub.count).to eq(1)
+      expect(binary_blob_stub.first).to have_attributes(
+        :data_type     => "png",
+        :md5           => "ce114e4501d2f4e2dcea3e17b546f339",
+        :part_size     => 14,
+        :resource_id   => picture.id,
+        :resource_type => "Picture",
+        :size          => 14,
+      )
+      expect(binary_blob_part_stub.first).to have_attributes(
+        :binary_blob_id => binary_blob_stub.first.id,
+        :data           => "This is a test",
+        :md5            => "ce114e4501d2f4e2dcea3e17b546f339",
+        :size           => 14,
+      )
+    end
+  end
+end