Rake：db迁移失败，并带有预先存在的mySQL数据库

Question

I am trying to create a rails instance with a pre-existing mySQL database and I am following this guide .

Steps 1-3 worked but when running the rails server, it says there are migrations pending.

I would be very grateful if someone could tell me where the error is stemming from or give some general pointers on how to integrate a pre-existing mySQL database with a rails app.

Running rake db:migrate yields this error

== 1 CreateDatabase: migrating ================================================
-- create_table("Bill", {:primary_key=>"confirmationNo", :id=>:integer, :force=>:cascade, :options=>"ENGINE=InnoDB DEFAULT CHARSET=latin1"})
   -> 0.0556s
-- create_table("Customer", {:primary_key=>"creditCardNo", :id=>:integer, :force=>:cascade, :options=>"ENGINE=InnoDB DEFAULT CHARSET=latin1"})
rake aborted!
StandardError: An error has occurred, all later migrations canceled:

Mysql2::Error: Cannot delete or update a parent row: a foreign key constraint fails: DROP TABLE `Customer` CASCADE

Here are my schema.rb and migrate/001_create_database.rb

schema.rb

ActiveRecord::Schema.define(version: 0) do

  create_table "Bill", primary_key: "confirmationNo", id: :integer, force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=latin1" do |t|
t.integer "pointsEarned",            null: false
t.float   "amountDue",    limit: 24, null: false
  end

  create_table "Customer", primary_key: "creditCardNo", id: :integer, force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=latin1" do |t|
t.integer "guestID",             null: false
t.string  "username", limit: 30
t.string  "name",     limit: 30, null: false
t.index ["guestID", "username"], name: "guestID", unique: true, using: :btree
t.index ["username"], name: "username", using: :btree
  end

  create_table "Manager", primary_key: "managerID", id: :integer, force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=latin1" do |t|
t.string "name", limit: 10, null: false
  end

  create_table "Reservation", primary_key: "confirmationNo", id: :integer, force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=latin1" do |t|
t.date    "inDate"
t.date    "outDate"
t.boolean "availability", null: false
t.integer "roomNo"
t.integer "creditCardNo"
t.index ["creditCardNo"], name: "creditCardNo", using: :btree
t.index ["inDate", "outDate"], name: "inDate", using: :btree
t.index ["roomNo"], name: "roomNo", using: :btree
  end

  create_table "Room", primary_key: "roomNo", id: :integer, force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=latin1" do |t|
t.string "roomType", limit: 30, null: false
t.index ["roomType"], name: "roomType", using: :btree
  end

  create_table "Roomtype", primary_key: "roomType", id: :string, limit: 30, force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=latin1" do |t|
t.integer "capacity",            null: false
t.float   "rate",     limit: 24, null: false
  end

  create_table "Stay", primary_key: ["inDate", "outDate"], force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=latin1" do |t|
t.date "inDate",  null: false
t.date "outDate", null: false
  end

  create_table "User", primary_key: "username", id: :string, limit: 1, force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=latin1" do |t|
t.integer "points", null: false
  end

  add_foreign_key "Bill", "Reservation", column: "confirmationNo", primary_key: "confirmationNo", name: "Bill_ibfk_1"
  add_foreign_key "Customer", "User", column: "username", primary_key: "username", name: "Customer_ibfk_1"
  add_foreign_key "Reservation", "Customer", column: "creditCardNo", primary_key: "creditCardNo", name: "Reservation_ibfk_3"
  add_foreign_key "Reservation", "Room", column: "roomNo", primary_key: "roomNo", name: "Reservation_ibfk_1"
  add_foreign_key "Reservation", "Stay", column: "inDate", primary_key: "inDate", name: "Reservation_ibfk_2", on_delete: :cascade
  add_foreign_key "Reservation", "Stay", column: "outDate", primary_key: "outDate", name: "Reservation_ibfk_2", on_delete: :cascade
  add_foreign_key "Room", "Roomtype", column: "roomType", primary_key: "roomType", name: "Room_ibfk_1"
end

migrate/001_create_database.rb

class CreateDatabase < ActiveRecord::Migration
  def self.up

ActiveRecord::Schema.define(version: 0) do

  create_table "Bill", primary_key: "confirmationNo", id: :integer, force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=latin1" do |t|
t.integer "pointsEarned",            null: false
t.float   "amountDue",    limit: 24, null: false
  end

  create_table "Customer", primary_key: "creditCardNo", id: :integer, force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=latin1" do |t|
t.integer "guestID",             null: false
t.string  "username", limit: 30
t.string  "name",     limit: 30, null: false
t.index ["guestID", "username"], name: "guestID", unique: true, using: :btree
t.index ["username"], name: "username", using: :btree
  end

  create_table "Manager", primary_key: "managerID", id: :integer, force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=latin1" do |t|
t.string "name", limit: 10, null: false
  end

  create_table "Reservation", primary_key: "confirmationNo", id: :integer, force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=latin1" do |t|
t.date    "inDate"
t.date    "outDate"
t.boolean "availability", null: false
t.integer "roomNo"
t.integer "creditCardNo"
t.index ["creditCardNo"], name: "creditCardNo", using: :btree
t.index ["inDate", "outDate"], name: "inDate", using: :btree
t.index ["roomNo"], name: "roomNo", using: :btree
  end

  create_table "Room", primary_key: "roomNo", id: :integer, force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=latin1" do |t|
t.string "roomType", limit: 30, null: false
t.index ["roomType"], name: "roomType", using: :btree
  end

  create_table "Roomtype", primary_key: "roomType", id: :string, limit: 30, force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=latin1" do |t|
t.integer "capacity",            null: false
t.float   "rate",     limit: 24, null: false
  end

  create_table "Stay", primary_key: ["inDate", "outDate"], force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=latin1" do |t|
t.date "inDate",  null: false
t.date "outDate", null: false
  end

  create_table "User", primary_key: "username", id: :string, limit: 1, force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=latin1" do |t|
t.integer "points", null: false
  end

  add_foreign_key "Bill", "Reservation", column: "confirmationNo", primary_key: "confirmationNo", name: "Bill_ibfk_1"
  add_foreign_key "Customer", "User", column: "username", primary_key: "username", name: "Customer_ibfk_1"
  add_foreign_key "Reservation", "Customer", column: "creditCardNo", primary_key: "creditCardNo", name: "Reservation_ibfk_3"
  add_foreign_key "Reservation", "Room", column: "roomNo", primary_key: "roomNo", name: "Reservation_ibfk_1"
  add_foreign_key "Reservation", "Stay", column: "inDate", primary_key: "inDate", name: "Reservation_ibfk_2", on_delete: :cascade
  add_foreign_key "Reservation", "Stay", column: "outDate", primary_key: "outDate", name: "Reservation_ibfk_2", on_delete: :cascade
  add_foreign_key "Room", "Roomtype", column: "roomType", primary_key: "roomType", name: "Room_ibfk_1"
end

  end

  def self.down
# drop all the tables if you really need
# to support migration back to version 0
  end
end

Cheers

Answer 1

Does your MySQL Database have a "schema_migrations" table? Rails relies on this table to decide if there are any migrations pending based on the version number in the database and schema.rb file. Update your schema.rb file so the version is in the standard format: "20170326120700" instead of "0" and then create a table "schema_migrations" with a field called "version" and insert the version number "20170326120700" into the new table. Rails should stop complaining about the pending migration. The "version" field should be type VARCHAR(255).

To bring the schema.rb in sync with the database again you can follow the process to recreate the schema.rb like you found in the tutorial "rake db:schema:dump". Verify your versions still match up in the schema.rb file and "schema_migrations" table.