1 files changed, 78 insertions, 0 deletions
diff --git a/db/migrate/20190129165720_migrate_auto_dev_ops_domain_to_cluster_domain.rb b/db/migrate/20190129165720_migrate_auto_dev_ops_domain_to_cluster_domain.rb
new file mode 100644
index 00000000000..2d3e9acaa62
--- /dev/null
+++ b/db/migrate/20190129165720_migrate_auto_dev_ops_domain_to_cluster_domain.rb
@@ -0,0 +1,78 @@
+# frozen_string_literal: true
+
+class MigrateAutoDevOpsDomainToClusterDomain < ActiveRecord::Migration[5.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def up
+    domains_info = connection.exec_query(project_auto_devops_query).rows
+    domains_info.each_slice(1_000) do |batch|
+      update_clusters_query = build_clusters_query(Hash[*batch.flatten])
+
+      connection.exec_query(update_clusters_query)
+    end
+  end
+
+  def down
+    # no-op
+  end
+
+  private
+
+  def project_auto_devops_table
+    @project_auto_devops_table ||= ProjectAutoDevops.arel_table
+  end
+
+  def cluster_projects_table
+    @cluster_projects_table ||= Clusters::Project.arel_table
+  end
+
+  # Fetches ProjectAutoDevops records with:
+  # - A domain set
+  # - With a Clusters::Project related to Project
+  #
+  # Returns an array of arrays like:
+  # => [
+  #     [177, "104.198.38.135.nip.io"],
+  #     [178, "35.232.213.111.nip.io"],
+  #     ...
+  #    ]
+  # Where the first element is the Cluster ID and
+  # the second element is the domain.
+  def project_auto_devops_query
+    project_auto_devops_table.join(cluster_projects_table, Arel::Nodes::OuterJoin)
+      .on(project_auto_devops_table[:project_id].eq(cluster_projects_table[:project_id]))
+      .where(project_auto_devops_table[:domain].not_eq(nil).and(project_auto_devops_table[:domain].not_eq('')))
+      .project(cluster_projects_table[:cluster_id], project_auto_devops_table[:domain])
+      .to_sql
+  end
+
+  # Returns an SQL UPDATE query using a CASE statement
+  # to update multiple cluster rows with different values.
+  #
+  # Example:
+  # UPDATE clusters
+  # SET domain = (CASE
+  #   WHEN id = 177 then '104.198.38.135.nip.io'
+  #   WHEN id = 178 then '35.232.213.111.nip.io'
+  #   WHEN id = 179 then '35.232.168.149.nip.io'
+  #   WHEN id = 180 then '35.224.116.88.nip.io'
+  # END)
+  # WHERE id IN (177,178,179,180);
+  def build_clusters_query(cluster_domains_info)
+    <<~HEREDOC
+    UPDATE clusters
+      SET domain = (CASE
+        #{cluster_when_statements(cluster_domains_info)}
+      END)
+    WHERE id IN (#{cluster_domains_info.keys.join(",")});
+    HEREDOC
+  end
+
+  def cluster_when_statements(cluster_domains_info)
+    cluster_domains_info.map do |cluster_id, domain|
+      "WHEN id = #{cluster_id} then '#{domain}'"
+    end.join("\n")
+  end
+end