如何在 Rails 迁移中创建这个特定的 PostGres 索引？答案

【问题标题】：How do I create this specific PostGres index in a Rails migration?如何在 Rails 迁移中创建这个特定的 PostGres 索引？
【发布时间】：2017-02-21 17:15:44
【问题描述】：

我使用的是 Rails 4.2.7 和 PostGres 9.5。我正在尝试在我的表上创建一个 trqm 索引（以方便 LIKE 搜索）所以我创建了这个迁移

class AddTrqmIndexOnRaceTimes < ActiveRecord::Migration
  def change
    CREATE INDEX my_object_times_name_gin_trgm_idx ON my_object_times USING gin (name gin_trgm_ops);
  end
end

当我运行“rake db:migrate”时，这会导致以下错误……

StandardError: An error has occurred, this and all later migrations canceled:

undefined local variable or method `gin_trgm_ops' for #<AddTrqmIndexOnRaceTimes:0x007fdc34b40600>
/Users/mikeb/.rvm/gems/ruby-2.3.0/gems/activerecord-4.2.7.1/lib/active_record/migration.rb:664:in `block in method_missing'
/Users/mikeb/.rvm/gems/ruby-2.3.0/gems/activerecord-4.2.7.1/lib/active_record/migration.rb:634:in `block in say_with_time'
/Users/mikeb/.rvm/gems/ruby-2.3.0/gems/activerecord-4.2.7.1/lib/active_record/migration.rb:634:in `say_with_time'
/Users/mikeb/.rvm/gems/ruby-2.3.0/gems/activerecord-4.2.7.1/lib/active_record/migration.rb:654:in `method_missing'
/Users/mikeb/Documents/workspace/runtrax/db/migrate/20161012185951_add_trqm_index_on_my_object_times.rb:3:in `change'
/Users/mikeb/.rvm/gems/ruby-2.3.0/gems/activerecord-4.2.7.1/lib/active_record/migration.rb:608:in `exec_migration'
/Users/mikeb/.rvm/gems/ruby-2.3.0/gems/activerecord-4.2.7.1/lib/active_record/migration.rb:592:in `block (2 levels) in migrate'
/Users/mikeb/.rvm/gems/ruby-2.3.0/gems/activerecord-4.2.7.1/lib/active_record/migration.rb:591:in `block in migrate'
/Users/mikeb/.rvm/gems/ruby-2.3.0/gems/activerecord-4.2.7.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:292:in `with_connection'
/Users/mikeb/.rvm/gems/ruby-2.3.0/gems/activerecord-4.2.7.1/lib/active_record/migration.rb:590:in `migrate'

在 Rails 迁移中创建此索引的正确方法是什么？

【问题讨论】：

标签： ruby-on-rails postgresql indexing migration gwt-gin

【解决方案1】：

您不能直接在 ruby 方法change 中添加 SQL。使用add_index 方法，或者如果您需要超越帮助程序的功能，请使用 ActiveRecord 执行您的查询，如下所示：

class AddTrqmIndexOnRaceTimes < ActiveRecord::Migration
  def change
    MyObjectTime.connection.execute("CREATE INDEX my_object_times_name_gin_trgm_idx ON my_object_times USING gin (name gin_trgm_ops);")
  end
end

【讨论】：

如何使用“add_index”方法来执行我在问题中指定的索引类型？

【解决方案2】：

Rails 5 添加了对在表达式索引上指定运算符类的支持

例如：

def change
  add_index :patients, 'lower(last_name) varchar_pattern_ops', name: "index_patients_on_name_unique", unique: true
end

source

【讨论】：

【解决方案3】：

您需要对您的代码稍作改动。将 sql 查询包装在 execute 中。

class AddTrqmIndexOnRaceTimes < ActiveRecord::Migration
  def change
    execute "CREATE INDEX my_object_times_name_gin_trgm_idx ON my_object_times USING gin (name gin_trgm_ops);"
  end
end

【讨论】：