ActiveRecord find_each 和 Postgres

Question

我收到以下错误：

PGError: ERROR:  operator does not exist: character varying >= integer
LINE 1: ...CT  "games".* FROM "games"  WHERE ("games"."uuid" >= 0) ORDE...
                                                             ^
HINT:  No operator matches the given name and argument type(s). You might need to add explicit type casts.
: SELECT  "games".* FROM "games"  WHERE ("games"."uuid" >= 0) ORDER BY "games"."uuid" ASC LIMIT 1000

当我尝试这样做时：

Game.find_each do |game|
  # ...
end

我的模型有一个字符串 (UUID) 主键：

class Game < ActiveRecord::Base
  self.primary_key = 'uuid'

  before_create do |game|
    game.uuid = UUIDTools::UUID.timestamp_create().to_s if game.uuid.blank?
  end
end

我不知道 ActiveRecord 为什么要放入 WHERE 子句，但这是完全没有必要的，也是类型错误的原因（因为它是字符串列，而不是整数列）。

那么，我该如何避免这种情况呢？我应该在我的模型定义中添加一些东西吗？或者我应该避免find_each 并使用不同的方法？这是一个 rake 任务，它只是遍历所有条目并查找一些附加信息......

Answer 1

似乎find_each 存在非数字主键的错误：

https://groups.google.com/group/compositekeys/browse_frm/month/2011-06

Answer 2

我认为不带任何参数的 find_each 将导致 find_by_id 其中 id >= 0。即使 ActiveRecord 使用正确的列，在您的情况下，它似乎并不知道该列是 varchar 类型，而是整数。

您可以尝试使用另一种查找方法，或者尝试在 find_each 中添加一些条件。

这可能与使用字符串作为主键的问题有关：http://railsforum.com/viewtopic.php?id=11110

干杯

Answer 3

此blog post 已修复您的错误：

在 lib/clean_find_in_batches.rb 中

module CleanFindInBatches

  def self.included(base)
    base.class_eval do
      alias :old_find_in_batches :find_in_batches
      alias :find_in_batches :replacement_find_in_batches
    end
  end

  # Override due to implementation of regular find_in_batches
  # conflicting using UUIDs
  def replacement_find_in_batches(options = {}, &block)
    relation = self
    return old_find_in_batches(options, &block) if relation.primary_key.is_a?(Arel::Attributes::Integer)
    # Throw errors like the real thing
    if (finder_options = options.except(:batch_size)).present?
      raise "You can't specify an order, it's forced to be #{batch_order}" if options[:order].present?
      raise "You can't specify a limit, it's forced to be the batch_size" if options[:limit].present?
      raise 'You can\'t specify start, it\'s forced to be 0 because the ID is a string' if options.delete(:start)
      relation = apply_finder_options(finder_options)
    end
    # Compute the batch size
    batch_size = options.delete(:batch_size) || 1000
    offset = 0
    # Get the relation and keep going over it until there's nothing left
    relation = relation.except(:order).order(batch_order).limit(batch_size)
    while (results = relation.offset(offset).limit(batch_size).all).any?
      block.call results
      offset += batch_size
    end
    nil
  end

end

在 config/initializers/clean_find_in_batches.rb 中

ActiveRecord::Batches.send(:include, CleanFindInBatches)