取决于：：destroy导致PostgreSQL错误

Question

class Accdist < ActiveRecord::Base
  has_many :accdistlavoraziones, dependent: :destroy

删除accdist时，控制台将输出以下内容：

 Accdist Load (27.3ms)  SELECT "accdists".* FROM "accdists" WHERE "accdists"."id" = $1 LIMIT 1  [["id", "1"]]
 Accdistlavorazione Load (20.2ms)  SELECT "accdistlavoraziones".* FROM "accdistlavoraziones" WHERE "accdistlavoraziones"."accdist_id" = 1
  SQL (59.7ms)  DELETE FROM "accdistlavoraziones" WHERE "accdistlavoraziones"."" = $1  [[nil, nil]]
PG::SyntaxError: ERROR:  zero-length delimited identifier at or near """"
LINE 1: ...OM "accdistlavoraziones" WHERE "accdistlavoraziones"."" = $1
                                                                ^
: DELETE FROM "accdistlavoraziones" WHERE "accdistlavoraziones"."" = $1
   (0.1ms)  ROLLBACK
Completed 500 Internal Server Error in 155.3ms

奇怪的是，如果我查询：

Accdistlavorazione.where('accdist_id = ?', 1).count
   (0.6ms)  SELECT COUNT(*) FROM "accdistlavoraziones" WHERE (accdist_id = 1)
 => 10

返回有效结果。

为什么内部机制导致postgresql处理nil（s）？

Answer 1

对于遇到此问题的任何人，可能发生的情况如下。
-通过rails快捷方式创建联接表has_and_belongs_to_many
-意识到您稍后需要进行has_many ... through:设置
-创建新联接记录的过程实际上正在运行...因为[...]_id正在引用。
–删除时间到了，您正在寻找连接表的ID，这自然是nil