rake db：migrate db：reset和db：schema：load之间的区别

本文翻译自：Difference between rake db:migrate db:reset and db:schema:load

The difference between rake db:migrate and rake db:reset is pretty clear in my head. rake db:migrate和rake db:reset之间的区别非常明显。 The thing which I don't understand is how rake db:schema:load different from the former two. 我不明白的是rake db:schema:load与前两个不同。

Just to be sure that I am on the same page: 只是为了确保我在同一页面上：

rake db:migrate - Runs the migrations which haven't been run yet. rake db:migrate - 运行尚未运行的迁移。
rake db:reset - Clears the database (presumably does a rake db:drop + rake db:create + rake db:migrate ) and runs migration on a fresh database. rake db:reset - 清除数据库（可能是rake db:drop + rake db:create + rake db:migrate ）并在新数据库上运行迁移。

Please help to clarify, if my understanding has gone wrong. 如果我的理解出错了，请帮助澄清一下。

#1楼

参考：https://stackoom.com/question/hDxy/rake-db-migrate-db-reset和db-schema-load之间的区别

#2楼

As far as I understand, it is going to drop your database and re-create it based on your db/schema.rb file. 据我所知，它将丢弃您的数据库并根据您的db/schema.rb文件重新创建它。 That is why you need to make sure that your schema.rb file is always up to date and under version control. 这就是为什么您需要确保schema.rb文件始终是最新的并且受版本控制。

#3楼

db:migrate runs (single) migrations that have not run yet. db：migrate运行尚未运行的（单个）迁移。
db:create creates the database db：create创建数据库
db:drop deletes the database db：drop删除数据库
db:schema:load creates tables and columns within the (existing) database following schema.rb db：schema：load在schema.rb之后的（现有）数据库中创建表和列
db:setup does db:create, db:schema:load, db:seed db：setup确实db：create，db：schema：load，db：seed
db:reset does db:drop, db:setup db：reset执行db：drop，db：setup

Typically, you would use db:migrate after having made changes to the schema via new migration files (this makes sense only if there is already data in the database). 通常，在通过新的迁移文件对架构进行更改后，您将使用db：migrate（仅当数据库中已存在数据时才有意义）。 db:schema:load is used when you setup a new instance of your app. db：schema：在设置应用程序的新实例时使用load。

I hope that helps. 我希望有所帮助。

UPDATE for rails 3.2.12: 更新rails 3.2.12：

I just checked the source and the dependencies are like this now: 我刚检查了源代码，依赖关系现在是这样的：

db:create creates the database for the current env db：create为当前环境创建数据库
db:create:all creates the databases for all envs db：create：all为所有env创建数据库
db:drop drops the database for the current env db：drop删除当前env的数据库
db:drop:all drops the databases for all envs db：drop：all删除所有envs的数据库
db:migrate runs migrations for the current env that have not run yet db：migrate为尚未运行的当前env运行迁移
db:migrate:up runs one specific migration db：migrate：up运行一个特定的迁移
db:migrate:down rolls back one specific migration db：migrate：down回滚一个特定的迁移
db:migrate:status shows current migration status db：migrate：status显示当前的迁移状态
db:rollback rolls back the last migration db：rollback回滚上次迁移
db:forward advances the current schema version to the next one db：forward将当前架构版本推进到下一个版本
db:seed (only) runs the db/seed.rb file db：seed （only）运行db / seed.rb文件
db:schema:load loads the schema into the current env's database db：schema：load将架构加载到当前env的数据库中
db:schema:dump dumps the current env's schema (and seems to create the db as well) db：schema：dump转储当前的env架构（并且似乎也创建了db）
db:setup runs db:schema:load, db:seed db：setup运行db：schema：load，db：seed
db:reset runs db:drop db:setup db：reset运行db：drop db：setup
db:migrate:redo runs (db:migrate:down db:migrate:up) or (db:rollback db:migrate) depending on the specified migration db：migrate：redo运行（db：migrate：down db：migrate：up）或（db：rollback db：migrate），具体取决于指定的迁移
db:migrate:reset runs db:drop db:create db:migrate db：migrate：reset运行db：drop db：create db：migrate

For further information please have a look at https://github.com/rails/rails/blob/v3.2.12/activerecord/lib/active_record/railties/databases.rake (for Rails 3.2.x) and https://github.com/rails/rails/blob/v4.0.5/activerecord/lib/active_record/railties/databases.rake (for Rails 4.0.x) 有关详细信息，请查看https://github.com/rails/rails/blob/v3.2.12/activerecord/lib/active_record/railties/databases.rake （对于Rails 3.2.x）和https：// github .com / rails / rails / blob / v4.0.5 / activerecord / lib / active_record / railties / databases.rake （对于Rails 4.0.x）

#4楼

You could simply look in the Active Record Rake tasks as that is where I believe they live as in this file. 您可以简单地查看Active Record Rake任务，因为我认为它们就像在此文件中一样存在。 https://github.com/rails/rails/blob/fe1f4b2ad56f010a4e9b93d547d63a15953d9dc2/activerecord/lib/active_record/tasks/database_tasks.rb https://github.com/rails/rails/blob/fe1f4b2ad56f010a4e9b93d547d63a15953d9dc2/activerecord/lib/active_record/tasks/database_tasks.rb

What they do is your question right? 他们做的是你的问题吗？

That depends on where they come from and this is just and example to show that they vary depending upon the task. 这取决于它们来自何处，这只是表明它们根据任务而变化的例子。 Here we have a different file full of tasks. 在这里，我们有一个完整的任务文件。

https://github.com/rails/rails/blob/fe1f4b2ad56f010a4e9b93d547d63a15953d9dc2/activerecord/Rakefile https://github.com/rails/rails/blob/fe1f4b2ad56f010a4e9b93d547d63a15953d9dc2/activerecord/Rakefile

which has these tasks. 有这些任务。

namespace :db do
  task create: ["db:mysql:build", "db:postgresql:build"]
  task drop: ["db:mysql:drop", "db:postgresql:drop"]
end

This may not answer your question but could give you some insight into go ahead and look the source over especially the rake files and tasks. 这可能无法解答您的问题，但可以让您深入了解并查看源代码，尤其是rake文件和任务。 As they do a pretty good job of helping you use rails they don't always document the code that well. 由于他们在帮助您使用rails方面做得非常好，因此并不总能很好地记录代码。 We could all help there if we know what it is supposed to do. 如果我们知道它应该做什么，我们都可以帮助那里。

#5楼

TLDR TLDR

Use 使用

rake db:migrate If you wanna make changes to the schema rake db:migrate如果您想对架构进行更改
rake db:reset If you wanna drop the database, reload the schema from schema.rb , and reseed the database rake db:reset如果要删除数据库，请从schema.rb重新加载模式，然后重新设置数据库
rake db:schema:load If you wanna reset database to schema as provided in schema.rb (This will delete all data) rake db:schema:load如果你想按照schema.rb规定将数据库重置为模式（这将删除所有数据）

Explanations 说明

rake db:schema:load will set up the schema as provided in schema.rb file. rake db:schema:load将设置schema.rb文件中提供的模式。 This is useful for a fresh install of app as it doesn't take as much time as db:migrate 这对于全新安装app非常有用，因为它不需要像db:migrate那样多的时间

Important note, db:schema:load will delete data on server. 重要提示， db:schema:load将删除服务器上的数据。

rake db:migrate makes changes to the existing schema. rake db:migrate对现有模式进行更改。 Its like creating versions of schema. 它就像创建架构版本一样。 db:migrate will look in db/migrate/ for any ruby files and execute the migrations that aren't run yet starting with the oldest. db:migrate将在db/migrate/查找任何ruby文件，并执行从最旧的文件开始尚未运行的迁移。 Rails knows which file is the oldest by looking at the timestamp at the beginning of the migration filename. 通过查看迁移文件名开头的时间戳，Rails知道哪个文件是最旧的。 db:migrate comes with a benefit that data can also be put in the database. db:migrate带来的好处是数据也可以放在数据库中。 This is actually not a good practice. 这实际上不是一个好习惯。 Its better to use rake db:seed to add data. 最好使用rake db:seed来添加数据。

rake db:migrate provides tasks up , down etc which enables commands like rake db:rollback and makes it the most useful command. rake db:migrate提供了up ， down等任务，可以启用rake db:rollback等命令，并使其成为最有用的命令。

rake db:reset does a db:drop and db:setup rake db:reset执行db:drop和db:setup
It drops the database, create it again, loads the schema, and initializes with the seed data 它删除数据库，再次创建它，加载模式，并使用种子数据进行初始化

Relevant part of the commands from databases.rake 来自databases.rake的相关命令部分

namespace :schema do
  desc 'Creates a db/schema.rb file that is portable against any DB supported by Active Record'
  task :dump => [:environment, :load_config] do
    require 'active_record/schema_dumper'
    filename = ENV['SCHEMA'] || File.join(ActiveRecord::Tasks::DatabaseTasks.db_dir, 'schema.rb')
    File.open(filename, "w:utf-8") do |file|
      ActiveRecord::SchemaDumper.dump(ActiveRecord::Base.connection, file)
    end
    db_namespace['schema:dump'].reenable
  end

  desc 'Loads a schema.rb file into the database'
  task :load => [:environment, :load_config, :check_protected_environments] do
    ActiveRecord::Tasks::DatabaseTasks.load_schema_current(:ruby, ENV['SCHEMA'])
  end

  # desc 'Drops and recreates the database from db/schema.rb for the current environment and loads the seeds.'
  task :reset => [ 'db:drop', 'db:setup' ]

namespace :migrate do
  # desc  'Rollbacks the database one migration and re migrate up (options: STEP=x, VERSION=x).'
  task :redo => [:environment, :load_config] do
    if ENV['VERSION']
      db_namespace['migrate:down'].invoke
      db_namespace['migrate:up'].invoke
    else
      db_namespace['rollback'].invoke
      db_namespace['migrate'].invoke
    end
  end

rake db：migrate db：reset和db：schema：load之间的区别

#1楼

#2楼

#3楼

#4楼

#5楼

TLDR TLDR

Explanations 说明

Relevant part of the commands from databases.rake 来自databases.rake的相关命令部分

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