Rails Active Record 中的原始 SQL 和 generate_series

Question

不知道给这个标题取什么名字，但我很难将原始 SQL 重写为 Rails ActiveRecord 方法。

我想提取所选日期范围内每个月的交易总和（总计）。

注意：需要显示该范围内的所有月份。 为此，我使用generate_series SQL 方法在该范围内生成一系列月份。

我正在编写的方法是在 Query 对象中，该对象具有一个现有关系，该关系是从以前过滤的事务。

我现在的功能：

  def group_total_by_months
   @relation.joins("RIGHT JOIN generate_series(TIMESTAMP '1-1-2018', TIMESTAMP '1-1-2020', interval '1 month') AS series
                     ON date_trunc('month', transactions.payment_date) = series")
            .group("series")
            .select("series AS payment_date, sum(transactions.total) AS total")
  end

结果：

#<ActiveRecord::AssociationRelation [#<Transaction id: nil, total: 0.61173e3, payment_date: "2019-06-01 00:00:00">, #<Transaction id: nil, total: 0.364446e4, payment_date: "2019-10-01 00:00:00">, #<Transaction id: nil, total: 0.1625e4, payment_date: "2019-08-01 00:00:00">]>    

这是按月计算的总和，但只有交易中存在的月数。为什么？因为生成的 SQL 看起来像这样，并且 FROM 子句来自所有事务，而不是过滤的事务：

    SELECT series AS payment_date, sum(transactions.total) AS total FROM \"transactions\" 
RIGHT JOIN generate_series(TIMESTAMP '1-1-2018', TIMESTAMP '1-1-2020', interval '1 month') AS series\n    ON date_trunc('month', transactions.payment_date) = series 
WHERE \"transactions\".\"account_id\" = 1 
GROUP BY series

我需要如下所示的 SQL：

WITH filteret_transactions AS (
    SELECT * FROM transactions WHERE transactions.account_id = 1
)

 SELECT series AS payment_date, sum(filteret_transactions.total) AS total 
    FROM  filteret_transactions
  RIGHT JOIN generate_series(TIMESTAMP '1-1-2018', TIMESTAMP '1-1-2020', interval '1 month') AS series
  ON date_trunc('month', filteret_transactions.payment_date) = series GROUP BY series

我怎样才能做到这一点？

Answer 1

您需要在加入之前应用条件。您可以将所需的参数作为参数传递，并像在第一种方法中一样进行查询。我已经在加入本身中添加了条件（如果需要，您可以添加更多）并使用模型本身（交易）来加入。

def group_total_by_months(account_id: )
   Transaction.joins("RIGHT JOIN generate_series(TIMESTAMP '1-1-2018', TIMESTAMP '1-1-2020', interval '1 month') AS series
                     ON date_trunc('month', transactions.payment_date) = series AND transactions\".\"account_id\" = #{account_id}")
            .group("series")
            .select("series AS payment_date, sum(transactions.total) AS total")
end

编辑：可能的解决方案（但不适用于所有情况）

您可以使用此方法（https://apidock.com/rails/ActiveRecord/Relation/where_values_hash）获取应用的 where 条件。创建一个查询条件并在原始查询中使用它。

def group_total_by_months

  applied_conditions = []

  @transation.where_values_hash.each do |p|
    applied_conditions << "AND #{p.first} = #{p.second}"
  end

  Transaction.joins("RIGHT JOIN generate_series(TIMESTAMP '1-1-2018', TIMESTAMP '1-1-2020', interval '1 month') AS series
                         ON date_trunc('month', transactions.payment_date) = series #{applied_conditions.join(' ')}")
                .group("series")
                .select("series AS payment_date, sum(transactions.total) AS total")
 end

注意

>> Project.where(id: 12).where_values_hash
>>  {"id"=>12}
>> Project.where('id = 12').where_values_hash
>> {}

参考：SQL join: where clause vs. on clause