如果在“rake db:schema:load”之后立即运行“rake db:migrate”,为什么schema.rb会被修改?

问题摘要:

我克隆了一个名为DMP Roadmap的开源项目,并遵循其安装指南直到 rake db:schema:load

那我会的 rake db:migrate rake db:迁移 不生成任何输出,这意味着不会更改任何内容,但架构文件已更改。

下面一定有什么事情,有谁知道数据库迁移的来龙去脉,请解释一下下面发生了什么?

复制步骤:

在Mac OS上,brew安装mariadb( brew info mariadb

跟随 installation guide :

git clone https://github.com/DMPRoadmap/roadmap.git
cd roadmap
cp config/database_example.yml config/database.yml
cp config/secrets_example.yml config/secrets.yml
cp config/branding_example.yml config/branding.yml
cp config/initializers/devise.rb.example config/initializers/devise.rb
cp config/initializers/recaptcha.rb.example config/initializers/recaptcha.rb
cp config/initializers/wicked_pdf.rb.example config/initializers/wicked_pdf.rb
bundle install
rake secret
vi config/secrets.yml # put the secret generated above into `config/secret.yml`
rake db:create
rake db:schema:load
rake db:migrate

rake db:迁移

 ActiveRecord::Schema.define(version: 20180508151824) do

   create_table "annotations", force: :cascade do |t|
-    t.integer  "question_id"
-    t.integer  "org_id"
-    t.text     "text"
-    t.integer  "type",        default: 0, null: false
+    t.integer  "question_id", limit: 4
+    t.integer  "org_id",      limit: 4
+    t.text     "text",        limit: 65535
+    t.integer  "type",        limit: 4,     default: 0, null: false
     t.datetime "created_at"
     t.datetime "updated_at"
   end

-  add_index "annotations", ["question_id"], name: "index_annotations_on_question_id"
+  add_index "annotations", ["org_id"], name: "fk_rails_aca7521f72", using: :btree
+  add_index "annotations", ["question_id"], name: "index_annotations_on_question_id", using: :btree

   create_table "answers", force: :cascade do |t|
-    t.text     "text"
-    t.integer  "plan_id"
-    t.integer  "user_id"
-    t.integer  "question_id"
+    t.text     "text",         limit: 65535
+    t.integer  "plan_id",      limit: 4
+    t.integer  "user_id",      limit: 4
+    t.integer  "question_id",  limit: 4
     t.datetime "created_at"
     t.datetime "updated_at"
-    t.integer  "lock_version", default: 0
+    t.integer  "lock_version", limit: 4,     default: 0
   end

-  add_index "answers", ["plan_id"], name: "index_answers_on_plan_id"
-  add_index "answers", ["question_id"], name: "index_answers_on_question_id"
+  add_index "answers", ["plan_id"], name: "index_answers_on_plan_id", using: :btree
+  add_index "answers", ["question_id"], name: "index_answers_on_question_id", using: :btree
+  add_index "answers", ["user_id"], name: "fk_rails_584be190c2", using: :btree

   create_table "answers_question_options", id: false, force: :cascade do |t|
-    t.integer "answer_id",          null: false

其他问题:

• 为什么要加一堆限制和树呢?
• 为什么加上这一行: + add_index "annotations", ["org_id"], name: "fk_rails_aca7521f72", using: :btree ? 它以前不在这里