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实例公共方法

decrement_counter(counter_name, id, by: 1, touch: nil)

通过直接 SQL 更新，将数字字段减一。

这与 increment_counter 的工作方式相同，但将列值减少 1，而不是增加它。

参数 ↑

  • counter_name - 应减一的字段名称。

  • id - 应减一的对象 ID 或 ID 数组。

  • :by - 减去值的量。默认为 1。

  • :touch - 更新时触碰时间戳列。传入 true 以触碰 updated_at 和/或 updated_on。传入符号以触碰该列，或传入符号数组以仅触碰那些列。

示例 ↑

# Decrement the posts_count column for the record with an id of 5
DiscussionBoard.decrement_counter(:posts_count, 5)

# Decrement the posts_count column for the record with an id of 5
by a specific amount.
DiscussionBoard.decrement_counter(:posts_count, 5, by: 3)

# Decrement the posts_count column for the record with an id of 5
# and update the updated_at value.
DiscussionBoard.decrement_counter(:posts_count, 5, touch: true)

来源： 显示 | 在 GitHub 上

# File activerecord/lib/active_record/counter_cache.rb, line 203
def decrement_counter(counter_name, id, by: 1, touch: nil)
  update_counters(id, counter_name => -by, touch: touch)
end

increment_counter(counter_name, id, by: 1, touch: nil)

通过直接 SQL 更新，将数字字段加一。

此方法主要用于维护 counter_cache 列，这些列用于存储聚合值。例如，DiscussionBoard 可以缓存 posts_count 和 comments_count，以避免在每次显示时运行 SQL 查询来计算帖子和评论的数量。

参数 ↑

  • counter_name - 应增加的字段名称。

  • id - 应增加的对象 ID 或 ID 数组。

  • :by - 增加值的量。默认为 1。

  • :touch - 更新时触碰时间戳列。传入 true 以触碰 updated_at 和/或 updated_on。传入符号以触碰该列，或传入符号数组以仅触碰那些列。

示例 ↑

# Increment the posts_count column for the record with an id of 5
DiscussionBoard.increment_counter(:posts_count, 5)

# Increment the posts_count column for the record with an id of 5
# by a specific amount.
DiscussionBoard.increment_counter(:posts_count, 5, by: 3)

# Increment the posts_count column for the record with an id of 5
# and update the updated_at value.
DiscussionBoard.increment_counter(:posts_count, 5, touch: true)

来源： 显示 | 在 GitHub 上

# File activerecord/lib/active_record/counter_cache.rb, line 173
def increment_counter(counter_name, id, by: 1, touch: nil)
  update_counters(id, counter_name => by, touch: touch)
end

reset_counters(id, *counters, touch: nil)

使用 SQL count 查询将一个或多个计数缓存重置为其正确值。这对于添加新的计数缓存，或者计数缓存已被损坏或直接通过 SQL 修改的情况非常有用。

参数 ↑

  • id - 您希望重置计数器的对象 ID 或 ID 数组。

  • counters - 要重置的一个或多个关联计数器。可以提供关联名称或计数器名称。

  • :touch - 更新时触碰时间戳列。传入 true 以触碰 updated_at 和/或 updated_on。传入符号以触碰该列，或传入符号数组以仅触碰那些列。

示例 ↑

# For the Post with id #1, reset the comments_count
Post.reset_counters(1, :comments)

# For posts with ids #1 and #2, reset the comments_count
Post.reset_counters([1, 2], :comments)

# Like above, but also touch the updated_at and/or updated_on
# attributes.
Post.reset_counters(1, :comments, touch: true)

来源： 显示 | 在 GitHub 上

# File activerecord/lib/active_record/counter_cache.rb, line 37
def reset_counters(id, *counters, touch: nil)
  ids = if composite_primary_key?
    if id.first.is_a?(Array)
      id
    else
      [id]
    end
  else
    Array(id)
  end

  updates = Hash.new { |h, k| h[k] = {} }

  counters.each do |counter_association|
    has_many_association = _reflect_on_association(counter_association)
    unless has_many_association
      has_many = reflect_on_all_associations(:has_many)
      has_many_association = has_many.find { |association| association.counter_cache_column && association.counter_cache_column.to_sym == counter_association.to_sym }
      counter_association = has_many_association.plural_name if has_many_association
    end
    raise ArgumentError, "'#{name}' has no association called '#{counter_association}'" unless has_many_association

    if has_many_association.is_a? ActiveRecord::Reflection::ThroughReflection
      has_many_association = has_many_association.through_reflection
    end

    counter_association = counter_association.to_sym
    foreign_key  = has_many_association.foreign_key.to_s
    child_class  = has_many_association.klass
    reflection   = child_class._reflections.values.find { |e| e.belongs_to? && e.foreign_key.to_s == foreign_key && e.options[:counter_cache].present? }
    counter_name = reflection.counter_cache_column

    counts =
      unscoped
        .joins(counter_association)
        .where(primary_key => ids)
        .group(primary_key)
        .count(:all)

    ids.each do |id|
      updates[id].merge!(counter_name => counts[id] || 0)
    end
  end

  if touch
    names = touch if touch != true
    names = Array.wrap(names)
    options = names.extract_options!
    touch_updates = touch_attributes_with_time(*names, **options)

    updates.each_value do |record_updates|
      record_updates.merge!(touch_updates)
    end
  end

  updates.each do |id, record_updates|
    unscoped.where(primary_key => [id]).update_all(record_updates)
  end

  true
end

update_counters(id, counters)

一个通用的“计数器更新器”实现，主要供 increment_counter 和 decrement_counter 使用，但也可单独使用。它只需对给定 ID 的记录执行直接 SQL 更新，并按照相应值指定的数量修改给定的计数器哈希。

参数 ↑

  • id - 您希望更新计数器的对象 ID 或 ID 数组。

  • counters - 一个 Hash，其中包含要更新的字段名称作为键，以及要更新字段的数量作为值。

  • :touch 选项 - 更新时触碰时间戳列。如果传递了属性名称，它们将与 updated_at/on 属性一起更新。

示例 ↑

# For the Post with id of 5, decrement the comments_count by 1, and
# increment the actions_count by 1
Post.update_counters 5, comments_count: -1, actions_count: 1
# Executes the following SQL:
# UPDATE posts
#    SET comments_count = COALESCE(comments_count, 0) - 1,
#        actions_count = COALESCE(actions_count, 0) + 1
#  WHERE id = 5

# For the Posts with id of 10 and 15, increment the comments_count by 1
Post.update_counters [10, 15], comments_count: 1
# Executes the following SQL:
# UPDATE posts
#    SET comments_count = COALESCE(comments_count, 0) + 1
#  WHERE id IN (10, 15)

# For the Posts with id of 10 and 15, increment the comments_count by 1
# and update the updated_at value for each counter.
Post.update_counters [10, 15], comments_count: 1, touch: true
# Executes the following SQL:
# UPDATE posts
#    SET comments_count = COALESCE(comments_count, 0) + 1,
#    `updated_at` = '2016-10-13T09:59:23-05:00'
#  WHERE id IN (10, 15)

来源： 显示 | 在 GitHub 上

# File activerecord/lib/active_record/counter_cache.rb, line 140
def update_counters(id, counters)
  id = [id] if composite_primary_key? && id.is_a?(Array) && !id[0].is_a?(Array)
  unscoped.where!(primary_key => id).update_counters(counters)
end