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Question

我试图通过检查它的几个关系来找到一个对象。

Loan.joins(:credit_memo_attributes)
    .where(credit_memo_attributes: {name: 'pr2_gtx1_y', value: '2014'})
    .where(credit_memo_attributes: {name: 'pr1_gtx1_y', value: '2013'})
    .where(credit_memo_attributes: {name: 'tx1_y', value: '2014'})

调用to_sql就可以了：

"SELECT `loans`.* FROM `loans` INNER JOIN `credit_memo_attributes` 
  ON `credit_memo_attributes`.`loan_id` = `loans`.`id` 
  WHERE `credit_memo_attributes`.`name` = 'pr2_gtx1_y' AND `credit_memo_attributes`.`value` = '2014' 
    AND `credit_memo_attributes`.`name` = 'pr1_gtx1_y' AND `credit_memo_attributes`.`value` = '2013' 
    AND `credit_memo_attributes`.`name` = 'tx1_y' AND `credit_memo_attributes`.`value` = '2014'"

所以，我正在检查具有所有这些属性的credit_memo_attributes的贷款。我知道我们的20,000笔贷款中至少有一笔符合此条件，但此查询返回一个空集。如果我只使用where子句中的一个，它会返回几个，正如我所期望的那样，但是一旦我再添加一个，它就是空的。

知道我哪里出错了？

Answer 1

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根据评论我相信您希望在您的条件中加入多个联接。你可以这样做：

attr_1 = {name: 'pr2_gtx1_y', value: '2014'}
attr_2 = {name: 'pr1_gtx1_y', value: '2013'}
attr_3 = {name: 'tx1_y', value: '2014'}

Loan.something_cool(attr_1, attr_2, attr_3)

class Loan < ActiveRecord::Base
...
def self.something_cool(attr_1, attr_2, attr_3)
  joins(sanitize_sql(["INNER JOIN credit_memo_attributes AS cma1 ON cma1.loan_id = loans.id AND cma1.name = :name AND cma1.value = :value", attr_1]))
    .joins(sanitize_sql(["INNER JOIN credit_memo_attributes AS cma2 ON cma2.loan_id = loans.id AND cma2.name = :name AND cma2.value = :value", attr_2]))
    .joins(sanitize_sql(["INNER JOIN credit_memo_attributes AS cma3 ON cma3.loan_id = loans.id AND cma3.name = :name AND cma3.value = :value", attr_3]))

end

如果您查看生成的SQL（包含在您的问题中，谢谢），您将看到所有这些条件正在进行AND运算。没有名称=＆＃39; pr2_gtx1_y＆＃39; AND name =＆＃39; pr1_gtx1_y＆＃39; （等等）。所以你得到了我期望的结果（没有行）。

Answer 2

您可以将所有名称和值放入数组中，如id和years，并将其传递到where子句中。 Active Record将查询数组中的所有值。

Loan.joins(:credit_memo_attributes)
    .where(credit_memo_attributes: {name: ids, value: years})

就我个人而言，我仍然在学习积极的记录，在这种担忧中我并不认为积极的记录支持多个where子句。

Answer 3

请注意SQL版本如何返回您的代码：它使用AND加入要求。

"SELECT `loans`.* FROM `loans` INNER JOIN `credit_memo_attributes` 
  ON `credit_memo_attributes`.`loan_id` = `loans`.`id` 
  WHERE `credit_memo_attributes`.`name` = 'pr2_gtx1_y' AND `credit_memo_attributes`.`value` = '2014' 
    AND `credit_memo_attributes`.`name` = 'pr1_gtx1_y' AND `credit_memo_attributes`.`value` = '2013' 
    AND `credit_memo_attributes`.`name` = 'tx1_y' AND `credit_memo_attributes`.`value` = '2014'"

现在，这几乎是不可能的。 Object.name永远不可能是pr2_gtx1_y，pr1_gtx1_y和tx1_y。 value属性也是如此。

这里需要的是OR，而不是AND。

为此，请尝试将查询更改为以下内容：

Loan.joins(:credit_memo_attributes)
  .where(
    "credit_memo_attributes.name = ? and credit_memo_attributes.value = ?
    OR credit_memo_attributes.names = ? and credit_memo_attributes.value = ?
    OR credit_memo_attributes.name = ? and credit_memo_attributes.value = ?",
    'pr2_gtx1_y', '2014',
    'pr1_gtx1_y', '2013',
    'tx1_y', '2014'
  )

ActiveRecord has_many有多个条件

3 个答案:

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