Commit 450b9f6e authored by Yorick Peterse's avatar Yorick Peterse

Merge branch 'da-port-cte-to-ce' into 'master'

Add Gitlab::SQL:CTE for easily building CTE statements

See merge request gitlab-org/gitlab-ce!19652
parents 9a4eadc8 ed3a1be1
---
title: Add Gitlab::SQL:CTE for easily building CTE statements
merge_request:
author:
type: added
module Gitlab
module SQL
# Class for easily building CTE statements.
#
# Example:
#
# cte = CTE.new(:my_cte_name)
# ns = Arel::Table.new(:namespaces)
#
# cte << Namespace.
# where(ns[:parent_id].eq(some_namespace_id))
#
# Namespace
# with(cte.to_arel).
# from(cte.alias_to(ns))
class CTE
attr_reader :table, :query
# name - The name of the CTE as a String or Symbol.
def initialize(name, query)
@table = Arel::Table.new(name)
@query = query
end
# Returns the Arel relation for this CTE.
def to_arel
sql = Arel::Nodes::SqlLiteral.new("(#{query.to_sql})")
Arel::Nodes::As.new(table, sql)
end
# Returns an "AS" statement that aliases the CTE name as the given table
# name. This allows one to trick ActiveRecord into thinking it's selecting
# from an actual table, when in reality it's selecting from a CTE.
#
# alias_table - The Arel table to use as the alias.
def alias_to(alias_table)
Arel::Nodes::As.new(table, alias_table)
end
# Applies the CTE to the given relation, returning a new one that will
# query from it.
def apply_to(relation)
relation.except(:where)
.with(to_arel)
.from(alias_to(relation.model.arel_table))
end
end
end
end
require 'spec_helper'
describe Gitlab::SQL::CTE, :postgresql do
describe '#to_arel' do
it 'generates an Arel relation for the CTE body' do
relation = User.where(id: 1)
cte = described_class.new(:cte_name, relation)
sql = cte.to_arel.to_sql
name = ActiveRecord::Base.connection.quote_table_name(:cte_name)
sql1 = ActiveRecord::Base.connection.unprepared_statement do
relation.except(:order).to_sql
end
expect(sql).to eq("#{name} AS (#{sql1})")
end
end
describe '#alias_to' do
it 'returns an alias for the CTE' do
cte = described_class.new(:cte_name, nil)
table = Arel::Table.new(:kittens)
source_name = ActiveRecord::Base.connection.quote_table_name(:cte_name)
alias_name = ActiveRecord::Base.connection.quote_table_name(:kittens)
expect(cte.alias_to(table).to_sql).to eq("#{source_name} AS #{alias_name}")
end
end
describe '#apply_to' do
it 'applies a CTE to an ActiveRecord::Relation' do
user = create(:user)
cte = described_class.new(:cte_name, User.where(id: user.id))
relation = cte.apply_to(User.all)
expect(relation.to_sql).to match(/WITH .+cte_name/)
expect(relation.to_a).to eq(User.where(id: user.id).to_a)
end
end
end
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