Arel 的多个 CTE

Question

我有一个 sql 格式如下的查询：

 with from as (#{select * query}),
 to as (#{another select *}),
 rates as (#{yet another select *})
 select rates.* from rates, from, to
 where rates.from_id = from.id and rates.to_id = to.id

如何将其转换为 Arel？我查看了 Arel CTE，但没有像上面的查询那样使用多个别名的示例。

Answer 1

这应该可以解决问题：

from_table = Arel::Table.new(:from)
to_table = Arel::Table.new(:to)
rates_table = Arel::Table.new(:rates)
query = rates_table.
  join(from_table).on(rates_table[:from_id].eq(from_table[:id])).
  join(to_table).on(rates_table[:to_id].eq(to_table[:id])).
  project(rates_table[Arel.star]).
  with([
    Arel::Nodes::As.new(from_table, Arel::Nodes::SqlLiteral.new("select * query")),
    Arel::Nodes::As.new(to_table, Arel::Nodes::SqlLiteral.new("another select *")),
    Arel::Nodes::As.new(rates_table, Arel::Nodes::SqlLiteral.new("yet another select *")),
  ])
puts query.to_sql

您应该将 Arel::Nodes::SqlLiteral.new("another select *") 表达式替换为实际的 Arel 查询。要从 ActiveRecord 关系中获取 Arel 查询，您可以对其调用 .ast。示例：User.where(active: true).ast.

Arel 的多个 CTE

Multiple CTEs with Arel

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arel