如何让 has_and_belongs_to_many 进行批量插入？

Question

我有两个具有has_and_belongs_to_many 关系的类。

class Customer < ApplicationRecord
  has_and_belongs_to_many :segments

  def rematch_segments
    self.segments = Segment.customer_segments(self)
  end
end

class Segment < ApplicationRecord
  has_and_belongs_to_many :customers

  class << self
    def customer_segments(customer)
      ...returns a collection of Segments...
    end
  end
end

调用rematch_segments 会为每个段插入。

(0.2ms)  BEGIN
Customer::HABTM_Segments Create (0.8ms)  INSERT INTO "customers_segments" ("customer_id", "segment_id", "created_at", "updated_at") VALUES ($1, $2, $3, $4)  [["customer_id", 1], ["segment_id", 1], ["created_at", "2020-03-24 23:42:52.985400"], ["updated_at", "2020-03-24 23:42:52.985400"]]
Customer::HABTM_Segments Create (0.2ms)  INSERT INTO "customers_segments" ("customer_id", "segment_id", "created_at", "updated_at") VALUES ($1, $2, $3, $4)  [["customer_id", 1], ["segment_id", 2], ["created_at", "2020-03-24 23:42:52.987537"], ["updated_at", "2020-03-24 23:42:52.987537"]]
Customer::HABTM_Segments Create (0.2ms)  INSERT INTO "customers_segments" ("customer_id", "segment_id", "created_at", "updated_at") VALUES ($1, $2, $3, $4)  [["customer_id", 1], ["segment_id", 3], ["created_at", "2020-03-24 23:42:52.988610"], ["updated_at", "2020-03-24 23:42:52.988610"]]
(0.3ms)  COMMIT

我怎样才能改为进行单个批量插入？

Answer 1

Rails 6 现在支持批量插入功能，可用于在单个查询中在数据库中插入多条记录。有一个insert_all 方法，它接受代表要插入数据库的每一行的哈希数组。默认情况下它会跳过重复的行

在单个 SQL INSERT 语句中将多条记录插入数据库。它不会实例化任何模型，也不会触发 Active Record 回调或验证。虽然传递的值要经过 Active Record 的类型转换和序列化。

attributes 参数是一个哈希数组。每个 Hash 确定单行的属性，并且必须具有相同的键。

表上的每个唯一索引都认为行是唯一的。跳过任何重复的行。用 :unique_by 覆盖（见下文）。

假设您有一个代表您的连接模型的 CustomerSegment 类。

你可以这样做：

CustomerSegment.insert_all([{ customer_id: 54, segment_id: 2 },{ customer_id: 143, segment_id: 222 }...])

Answer 2

您可以通过为您的联接表创建一个类来使关联可见：

class Customer < ApplicationRecord
  has_many :segments, through: :customer_segments
  has_many :customer_segments
end

class Segment < ApplicationRecord
  has_many :customers, through: :customer_segments
  has_many :customer_segments
end

class CustomerSegment < ApplicationRecord
  belongs_to :customer
  belongs_to :segment
end

这样您就可以使用 Rails 6 的 insert_all()（或 activerecord-import gem）直接批量插入连接表：

CustomerSegment.insert_all([
  { customer_id: 1, segment_id: 1 },
  { customer_id: 1, segment_id: 2 },
  …
])

Answer 3

如果您关注性能，我建议您使用原始 SQL 而不是 ORM，因为它可能相对具有性能缺陷。

为了简化代码，删除了 ['created_at', 'updated_at']。

1。使用原始查询

您可以考虑像下面这样构建 INSERT QUERY。

INSERT INTO customers_segments (customer_id,segment_id) VALUES (1,1),(1,2),(1,3) ...

根据记录大小，您可能需要设置批量大小。通常，应该没问题 无需批量即可管理数千条记录。

segments = Segment.find_by_attr(:attr_val) #please do not forget indexing of the attr in DB.
customer = Customer.create
stmt = segments.map {|seg| "(#{customer.id},#{seg.id})"}.join(",")

ActiveRecord::Base.connection.execute("INSERT INTO customers_segments (customer_id, segment_id) VALUES #{stmt}")

2。使用 ORM 实现原始查询

class Customer < ApplicationRecord
  ...
  def batch_rematch(attr_array)
    attr_val = attr_array.map{|a| %Q{'#{a}'} }.uniq.join(",")
    self.connection.execute(%Q{insert into customers_segments (customer_id,segment_id) 
                     select distinct customers.id,segments.id 
                     from customers,segments
                     where customers.id = #{self.id} 
                     and segments.<attr> in (#{attr_val})})
  end
end