Prepare for zero downtime migrationszero-downtime-migrations

Starting with GitLab 9.1.0 we will no longer allow downtime migrations
unless absolutely necessary. This commit updates the various developer
guides and adds code that is necessary to make zero downtime migrations
less painful.

1 files changed, 38 insertions, 0 deletions

diff --git a/spec/models/concerns/ignorable_column_spec.rb b/spec/models/concerns/ignorable_column_spec.rb
new file mode 100644
index 00000000000..dba9fe43327
--- /dev/null
+++ b/spec/models/concerns/ignorable_column_spec.rb
@@ -0,0 +1,38 @@
+require 'spec_helper'
+
+describe IgnorableColumn do
+  let :base_class do
+    Class.new do
+      def self.columns
+        # This method does not have access to "double"
+        [Struct.new(:name).new('id'), Struct.new(:name).new('title')]
+      end
+    end
+  end
+
+  let :model do
+    Class.new(base_class) do
+      include IgnorableColumn
+    end
+  end
+
+  describe '.columns' do
+    it 'returns the columns, excluding the ignored ones' do
+      model.ignore_column(:title)
+
+      expect(model.columns.map(&:name)).to eq(%w(id))
+    end
+  end
+
+  describe '.ignored_columns' do
+    it 'returns a Set' do
+      expect(model.ignored_columns).to be_an_instance_of(Set)
+    end
+
+    it 'returns the names of the ignored columns' do
+      model.ignore_column(:title)
+
+      expect(model.ignored_columns).to eq(Set.new(%w(title)))
+    end
+  end
+end