From 48aff82709769b098321c738f3444b9bdaa694c6 Mon Sep 17 00:00:00 2001
From: GitLab Bot <gitlab-bot@gitlab.com>
Date: Wed, 21 Oct 2020 07:08:36 +0000
Subject: Add latest changes from gitlab-org/gitlab@13-5-stable-ee

---
 lib/gitlab/database/bulk_update.rb | 168 +++++++++++++++++++++++++++++++++++++
 1 file changed, 168 insertions(+)
 create mode 100644 lib/gitlab/database/bulk_update.rb

(limited to 'lib/gitlab/database/bulk_update.rb')

diff --git a/lib/gitlab/database/bulk_update.rb b/lib/gitlab/database/bulk_update.rb
new file mode 100644
index 00000000000..1403d561890
--- /dev/null
+++ b/lib/gitlab/database/bulk_update.rb
@@ -0,0 +1,168 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Database
+    # Constructs queries of the form:
+    #
+    #   with cte(a, b, c) as (
+    #     select * from (values (:x, :y, :z), (:q, :r, :s)) as t
+    #     )
+    #   update table set b = cte.b, c = cte.c where a = cte.a
+    #
+    # Which is useful if you want to update a set of records in a single query
+    # but cannot express the update as a calculation (i.e. you have arbitrary
+    # updates to perform).
+    #
+    # The requirements are that the table must have an ID column used to
+    # identify the rows to be updated.
+    #
+    # Usage:
+    #
+    #  mapping = {
+    #    issue_a => { title: 'This title', relative_position: 100 },
+    #    issue_b => { title: 'That title', relative_position: 173 }
+    #  }
+    #
+    #  ::Gitlab::Database::BulkUpdate.execute(%i[title relative_position], mapping)
+    #
+    # Note that this is a very low level tool, and operates on the raw column
+    # values. Enums/state fields must be translated into their underlying
+    # representations, for example, and no hooks will be called.
+    #
+    module BulkUpdate
+      LIST_SEPARATOR = ', '
+
+      class Setter
+        include Gitlab::Utils::StrongMemoize
+
+        def initialize(model, columns, mapping)
+          @table_name = model.table_name
+          @connection = model.connection
+          @columns = self.class.column_definitions(model, columns)
+          @mapping = self.class.value_mapping(mapping)
+        end
+
+        def update!
+          if without_prepared_statement?
+            # A workaround for https://github.com/rails/rails/issues/24893
+            # When prepared statements are prevented (such as when using the
+            # query counter or in omnibus by default), we cannot call
+            # `exec_update`, since that will discard the bindings.
+            connection.send(:exec_no_cache, sql, log_name, params) # rubocop: disable GitlabSecurity/PublicSend
+          else
+            connection.exec_update(sql, log_name, params)
+          end
+        end
+
+        def self.column_definitions(model, columns)
+          raise ArgumentError, 'invalid columns' if columns.blank? || columns.any? { |c| !c.is_a?(Symbol) }
+          raise ArgumentError, 'cannot set ID' if columns.include?(:id)
+
+          ([:id] | columns).map { |name| column_definition(model, name) }
+        end
+
+        def self.column_definition(model, name)
+          definition = model.column_for_attribute(name)
+          raise ArgumentError, "Unknown column: #{name}" unless definition.type
+
+          definition
+        end
+
+        def self.value_mapping(mapping)
+          raise ArgumentError, 'invalid mapping' if mapping.blank?
+          raise ArgumentError, 'invalid mapping value' if mapping.any? { |_k, v| !v.is_a?(Hash) }
+
+          mapping
+        end
+
+        private
+
+        attr_reader :table_name, :connection, :columns, :mapping
+
+        def log_name
+          strong_memoize(:log_name) do
+            "BulkUpdate #{table_name} #{columns.drop(1).map(&:name)}:#{mapping.size}"
+          end
+        end
+
+        def params
+          mapping.flat_map do |k, v|
+            obj_id = k.try(:id) || k
+            v = v.merge(id: obj_id)
+            columns.map { |c| query_attribute(c, k, v.with_indifferent_access) }
+          end
+        end
+
+        # A workaround for https://github.com/rails/rails/issues/24893
+        # We need to detect if prepared statements have been disabled.
+        def without_prepared_statement?
+          strong_memoize(:without_prepared_statement) do
+            connection.send(:without_prepared_statement?, [1]) # rubocop: disable GitlabSecurity/PublicSend
+          end
+        end
+
+        def query_attribute(column, key, values)
+          value = values[column.name]
+          key[column.name] = value if key.try(:id) # optimistic update
+          ActiveRecord::Relation::QueryAttribute.from_user(nil, value, ActiveModel::Type.lookup(column.type))
+        end
+
+        def values
+          counter = 0
+          typed = false
+
+          mapping.map do |k, v|
+            binds = columns.map do |c|
+              bind = "$#{counter += 1}"
+              # PG is not great at inferring types - help it for the first row.
+              bind += "::#{c.sql_type}" unless typed
+              bind
+            end
+            typed = true
+
+            "(#{list_of(binds)})"
+          end
+        end
+
+        def list_of(list)
+          list.join(LIST_SEPARATOR)
+        end
+
+        def sql
+          <<~SQL
+            WITH cte(#{list_of(cte_columns)}) AS (VALUES #{list_of(values)})
+            UPDATE #{table_name} SET #{list_of(updates)} FROM cte WHERE cte_id = id
+          SQL
+        end
+
+        def column_names
+          strong_memoize(:column_names) { columns.map(&:name) }
+        end
+
+        def cte_columns
+          strong_memoize(:cte_columns) do
+            column_names.map do |c|
+              connection.quote_column_name("cte_#{c}")
+            end
+          end
+        end
+
+        def updates
+          column_names.zip(cte_columns).drop(1).map do |dest, src|
+            "#{connection.quote_column_name(dest)} = cte.#{src}"
+          end
+        end
+      end
+
+      def self.execute(columns, mapping, &to_class)
+        raise ArgumentError if mapping.blank?
+
+        entries_by_class = mapping.group_by { |k, v| block_given? ? to_class.call(k) : k.class }
+
+        entries_by_class.each do |model, entries|
+          Setter.new(model, columns, entries).update!
+        end
+      end
+    end
+  end
+end
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