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我想为平均评级添加一个物化视图。

我的费率模型是：

class Rating < ApplicationRecord
  belongs_to :post
  validates_presence_of :rate
  validates_inclusion_of :rate,in: 1..5
end

我的帖子模型是：

class Post < ActiveRecord::Base
  has_many :ratings
  accepts_nested_attributes_for :ratings
end

我想为帖子找到平均使用物化视图作为

<%= "Avg.rate:#{post.ratings.average(:rate).to_f.round(2)}"%><br>

我为 MV 创建了一个迁移

class CreateAvgMatView < ActiveRecord::Migration[5.1]
  def change
    execute <<-SQL
      CREATE MATERIALIZED VIEW rateavg_matview AS
      SELECT AVG("ratings"."rate") FROM "ratings"
    SQL
  end
end

我发现一个问题

D013:post_app naren$ rake db:migrate
== 20180813080437 CreateAvgMatView: migrating =================================
-- execute("      CREATE MATERIALIZED VIEW rateavg_matview AS\n        SELECT AVG(\"ratings\".\"rate\") FROM \"ratings\"\n\n")
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:

SQLite3::SQLException: near "MATERIALIZED": syntax error:       CREATE MATERIALIZED VIEW rateavg_matview AS
        SELECT AVG("ratings"."rate") FROM "ratings"
4

1 回答 1

1

SQLite 不支持物化视图。请在此处阅读更多内容如何在 sqlite 中创建物化视图？

您必须切换到不同的 RDMS（例如 PostgreSQL）或创建一个“普通”表并使用触发器来更新它。

于 2018-08-13T09:59:52.147 回答