Up & Down Again: A Migration's Tale

You run rake db:migrate and rake db:schema:load regularly, but what do they actually do? How does rake db:rollback automatically reverse migrations and why can't it reverse all of them? How can you teach these tasks new tricks to support additional database constructs?

We'll answer all of this and more as we explore the world of schema management in Rails. You will leave this talk with a deep understanding of how Rails manages schema, a better idea of its pitfalls, and ready to bend it to your will.

Transcript

1. Up & Down Again
   A Migration's Tale
   

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2. Derek Prior
   @derekprior
   

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3. View Slide

4. Schema
   Management
   @derekprior
   

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5. 0.10.1
   @derekprior
   

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6. Agenda
   @derekprior
   

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7. Agenda
   → Anatomy of a Migration
   @derekprior
   

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8. Agenda
   → Anatomy of a Migration
   → Applying and Reverting a Migration
   @derekprior
   

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9. Agenda
   → Anatomy of a Migration
   → Applying and Reverting a Migration
   → Schema Dumping
   @derekprior
   

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10. Agenda
    → Anatomy of a Migration
    → Applying and Reverting a Migration
    → Schema Dumping
    → Shortcomings and Extensions
    @derekprior
    

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11. Anatomy of a
    Migration
    @derekprior
    

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12. class CreatePosts < ActiveRecord::Migration[5.2]
    def change
    create_table :posts do |t|
    t.belongs_to :user, null: false, index: true, foreign_key: true
    t.string :title, null: false, index: { unique: true }
    t.text :body, null: false
    t.timestamps null: false, index: true
    end
    end
    end
    @derekprior
    

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13. class CreatePosts < ActiveRecord::Migration[5.2]
    def change
    create_table :posts do |t|
    t.belongs_to :user, null: false, index: true, foreign_key: true
    t.string :title, null: false, index: { unique: true }
    t.text :body, null: false
    t.timestamps null: false, index: true
    end
    end
    end
    @derekprior
    

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14. ActiveRecord::Migration
    def self.[](version)
    Compatibility.find(version)
    end
    module Compatibility
    def self.find(version)
    name = "V#{version.tr('.', '_')}"
    # Some error handling...
    const_get(name)
    end
    end
    @derekprior
    

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15. ActiveRecord::Migration
    def self.[](version)
    Compatibility.find(version)
    end
    module Compatibility
    def self.find(version)
    name = "V#{version.tr('.', '_')}"
    # Some error handling...
    const_get(name)
    end
    end
    @derekprior
    

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16. ActiveRecord::Migration[5.2]
    @derekprior
    

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17. ActiveRecord::Migration::Compatibility::V5_2
    @derekprior
    

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18. Compatibility::V5_2
    module ActiveRecord
    class Migration
    module Compatibility
    class V5_2 < Migration
    end
    end
    end
    end
    @derekprior
    

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19. Prevent Subclassing Migration
    module ActiveRecord
    class Migration
    def self.inherited(subclass)
    super
    if subclass.superclass == Migration
    raise StandardError, "Directly inheriting ... is not supported. "
    end
    end
    end
    end
    @derekprior
    

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20. class CreatePosts < ActiveRecord::Migration[5.1]
    def change
    create_table :posts do |t|
    t.belongs_to :user, null: false, index: true, foreign_key: true
    t.string :title, null: false, index: { unique: true }
    t.text :body, null: false
    t.timestamps null: false, index: true
    end
    end
    end
    @derekprior
    

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21. Compatibility::V5_1
    class V5_1 < V5_2
    def change_column(table_name, column_name, type, options = {})
    if adapter_name == "PostgreSQL"
    #...
    else
    super
    end
    end
    def create_table(table_name, options = {})
    if adapter_name == "Mysql2"
    #...
    else
    super
    end
    end
    end
    @derekprior
    

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22. Compatibility::V5_1
    class V5_1 < V5_2
    def change_column(table_name, column_name, type, options = {})
    if adapter_name == "PostgreSQL"
    #...
    else
    super
    end
    end
    def create_table(table_name, options = {})
    if adapter_name == "Mysql2"
    #...
    else
    super
    end
    end
    end
    @derekprior
    

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23. Compatibility::V5_1
    class V5_1 < V5_2
    def change_column(table_name, column_name, type, options = {})
    if adapter_name == "PostgreSQL"
    #...
    else
    super
    end
    end
    def create_table(table_name, options = {})
    if adapter_name == "Mysql2"
    #...
    else
    super
    end
    end
    end
    @derekprior
    

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24. Stable
    Migrations
    @derekprior
    

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25. !
    @derekprior
    

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26. class CreatePosts < ActiveRecord::Migration[5.2]
    def change
    create_table :posts do |t|
    t.belongs_to :user, null: false, index: true, foreign_key: true
    t.string :title, null: false, index: { unique: true }
    t.text :body, null: false
    t.timestamps null: false, index: true
    end
    end
    end
    @derekprior
    

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27. class CreatePosts < ActiveRecord::Migration[5.2]
    def change
    create_table :posts do |t|
    t.belongs_to :user, null: false, index: true, foreign_key: true
    t.string :title, null: false, index: { unique: true }
    t.text :body, null: false
    t.timestamps null: false, index: true
    end
    end
    end
    @derekprior
    

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28. Schema
    Statements
    @derekprior
    

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29. ActiveRecord::ConnectionAdapters::SchemaStatements
    @derekprior
    

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30. create_table :posts do |t|
    t.belongs_to :user, null: false, index: true, foreign_key: true
    t.string :title, null: false, index: { unique: true }
    t.text :body, null: false
    t.timestamps null: false, index: true
    end
    @derekprior
    

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31. create_table :posts do |t|
    t.belongs_to :user, null: false, index: true, foreign_key: true
    t.string :title, null: false, index: { unique: true }
    t.text :body, null: false
    t.timestamps null: false, index: true
    end
    @derekprior
    

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32. Jobs To Be Done
    @derekprior
    

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33. Jobs To Be Done
    → Adds non nullable user_id to CREATE TABLE
    @derekprior
    

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34. Jobs To Be Done
    → Adds non nullable user_id to CREATE TABLE
    → Adds an index to the user_id column
    @derekprior
    

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35. Jobs To Be Done
    → Adds non nullable user_id to CREATE TABLE
    → Adds an index to the user_id column
    → Adds a foreign key to the users table
    @derekprior
    

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36. class CreatePosts < ActiveRecord::Migration[5.2]
    def change
    create_table :posts do |t|
    t.belongs_to :user, null: false, index: true, foreign_key: true
    t.string :title, null: false, index: { unique: true }
    t.text :body, null: false
    t.timestamps null: false, index: true
    end
    end
    end
    @derekprior
    

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37. Postgres
    CREATE TABLE "posts" (
    "id" bigserial primary key,
    "title" character varying NOT NULL,
    "body" text NOT NULL,
    "user_id" bigint NOT NULL,
    "created_at" timestamp NOT NULL,
    "updated_at" timestamp NOT NULL,
    CONSTRAINT "fk_rails_5b5ddfd518"
    FOREIGN KEY ("user_id")
    REFERENCES "users" ("id")
    );
    CREATE UNIQUE INDEX "index_posts_on_title" ON "posts" ("title");
    CREATE INDEX "index_posts_on_user_id" ON "posts" ("user_id");
    CREATE INDEX "index_posts_on_created_at" ON "posts" ("created_at");
    CREATE INDEX "index_posts_on_updated_at" ON "posts" ("updated_at");
    @derekprior
    

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38. MySQL
    CREATE TABLE `posts` (
    `id` bigint NOT NULL AUTO_INCREMENT PRIMARY KEY,
    `title` varchar(255) NOT NULL,
    `body` text NOT NULL,
    `user_id` bigint NOT NULL,
    `created_at` datetime NOT NULL,
    `updated_at` datetime NOT NULL,
    UNIQUE INDEX `index_posts_on_title` (`title`),
    INDEX `index_posts_on_user_id` (`user_id`),
    INDEX `index_posts_on_created_at` (`created_at`),
    INDEX `index_posts_on_updated_at` (`updated_at`),
    CONSTRAINT `fk_rails_5b5ddfd518`
    FOREIGN KEY (`user_id`)
    REFERENCES `users` (`id`)
    );
    @derekprior
    

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39. Adatper
    Pattern
    @derekprior
    

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40. Adapter Pattern
    "Convert the interface of a class into another
    interface clients expect. Adapter lets classes work
    together that couldn't otherwise because of
    incompatible interfaces."
    -- Design Patterns (Gang of Four)
    @derekprior
    

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41. External Dependencies
    @derekprior
    

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42. External Dependencies
    → Postgres
    @derekprior
    

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43. External Dependencies
    → Postgres
    → MySQL
    @derekprior
    

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44. External Dependencies
    → Postgres
    → MySQL
    → SQLite
    @derekprior
    

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45. External Dependencies
    → Postgres
    → MySQL
    → SQLite
    → ...
    @derekprior
    

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46. Connection Adapters
    @derekprior
    

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47. Connection Adapters
    → AbstractAdapter
    @derekprior
    

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48. Connection Adapters
    → AbstractAdapter
    → PostgreSQLAdapter
    @derekprior
    

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49. Connection Adapters
    → AbstractAdapter
    → PostgreSQLAdapter
    → Mysql2Adapter
    @derekprior
    

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50. Connection Adapters
    → AbstractAdapter
    → PostgreSQLAdapter
    → Mysql2Adapter
    → SQLite3Adapter
    @derekprior
    

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51. Connection Adapters
    → AbstractAdapter
    → PostgreSQLAdapter
    → Mysql2Adapter
    → SQLite3Adapter
    → ...
    @derekprior
    

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52. Connection Adapter Responsibilities
    @derekprior
    

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53. Connection Adapter Responsibilities
    → Schema inspection
    @derekprior
    

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54. Connection Adapter Responsibilities
    → Schema inspection
    → Schema statements
    @derekprior
    

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55. Connection Adapter Responsibilities
    → Schema inspection
    → Schema statements
    → Mapping types
    @derekprior
    

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56. Connection Adapter Responsibilities
    → Schema inspection
    → Schema statements
    → Mapping types
    → Cataloging capabilities
    @derekprior
    

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57. Connection Adapter Responsibilities
    → Schema inspection
    → Schema statements
    → Mapping types
    → Cataloging capabilities
    → Quoting
    @derekprior
    

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58. Agenda
    → Anatomy of a Migration
    → Applying and Reverting a Migration
    → Schema Dumping
    → Shortcomings and Extensions
    @derekprior
    

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59. Applying a
    Migration
    @derekprior
    

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60. rails db:migrate
    @derekprior
    

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61. Which
    Migrations
    Will Run?
    @derekprior
    

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62. 20180327012835_create_posts.rb
    @derekprior
    

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63. What's in a Filename?
    20180327012835 create_posts
    version name
    @derekprior
    

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64. SELECT "schema_migrations"."version"
    FROM "schema_migrations"
    ORDER BY "schema_migrations"."version" ASC
    @derekprior
    

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65. INSERT INTO "schema_migrations" ("version")
    VALUES ($1) RETURNING "version"
    [["version", "20180327012835"]]
    @derekprior
    

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66. rails db:migrate:status
    @derekprior
    

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67. rails db:migrate:status
    Status Migration ID Migration Name
    up 20180327005927 Create users
    down 20180327012835 Create posts
    @derekprior
    

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68. rails db:migrate:status
    Status Migration ID Migration Name
    up 20180327005927 Create users
    up 20180327012835 ** NO FILE **
    @derekprior
    

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69. Rolling Back a
    Migration
    @derekprior
    

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70. With a down method
    def up
    add_column :users, :name, :string
    remove_column :users, :first_name
    remove_column :users, :last_name
    end
    def down
    add_column :users, :first_name, :string
    add_column :users, :last_name, :string
    remove_column :users: name
    end
    @derekprior
    

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71. With a change method
    def change
    add_column :users, :name, :string
    remove_column :users, :first_name
    remove_column :users, :last_name
    end
    @derekprior
    

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72. Down For
    Free
    @derekprior
    

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73. ActiveRecord::Migration::CommandRecorder
    def initialize(delegate = nil)
    @commands = []
    end
    def record(*command, &block)
    @commands << (command << block)
    end
    @derekprior
    

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74. ActiveRecord::Migration::CommandRecorder
    def create_table(*args, &block)
    record(:create_table, args, block)
    end
    def add_index(*args, &block)
    record(:add_index, args, block)
    end
    @derekprior
    

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75. ActiveRecord::Migration::CommandRecorder
    def invert_create_table(args, &block)
    [:drop_table, args, block]
    end
    def invert_add_index(args, &block)
    [:remove_index, args, block]
    end
    def invert_rename_table(args)
    [:rename_table, args.reverse]
    end
    @derekprior
    

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76. Is This Migration Reversible?
    def change
    add_column :users, :name, :string
    remove_column :users, :first_name
    remove_column :users, :last_name
    end
    @derekprior
    

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77. ActiveRecord::IrreversibleMigration
    remove_column is only reversible if given a type
    @derekprior
    

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78. def change
    add_column :users, :name, :string
    remove_column :users, :first_name
    remove_column :users, :last_name
    end
    @derekprior
    

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79. def change
    add_column :users, :name, :string
    remove_column :users, :first_name, :string
    remove_column :users, :last_name, :string
    end
    @derekprior
    

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80. def change
    add_column :users, :name, :string
    remove_column :users, :first_name, :string
    remove_column :users, :last_name, :string
    end
    @derekprior
    

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81. What Did We Record?
    [
    [:add_column, [:users, :name, :string]],
    [:remove_column, [:users, :first_name, :string]],
    [:remove_column, [:users, :last_name, :string]],
    ]
    @derekprior
    

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82. Inverted
    [
    [:add_column, [:users, :first_name, :string]
    [:add_column, [:users, :last_name, :string]
    [:remove_column, [:users, :name]],
    ]
    @derekprior
    

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83. !
    @derekprior
    

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84. !
    @derekprior
    

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85. What if a removed column originally had...
    @derekprior
    

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86. What if a removed column originally had...
    → A null: false constraint?
    @derekprior
    

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87. What if a removed column originally had...
    → A null: false constraint?
    → A default value?
    @derekprior
    

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88. What if a removed column originally had...
    → A null: false constraint?
    → A default value?
    → A foreign key?
    @derekprior
    

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89. It's Not Magic
    @derekprior
    

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90. Agenda
    → Anatomy of a Migration
    → Applying and Reverting a Migration
    → Schema Dumping
    → Shortcomings and Extensions
    @derekprior
    

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91. # This file is auto-generated from the current state of the database.
    # ...
    ActiveRecord::Schema.define(version: 2018_03_27_012835) do
    enable_extension "plpgsql"
    create_table "posts", force: :cascade do |t|
    t.string "title", null: false
    #...
    end
    create_table "users", force: :cascade do |t|
    t.string "email", null: false
    #...
    end
    add_foreign_key "posts", "users"
    end
    @derekprior
    

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92. How is it
    Generated?
    @derekprior
    

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93. ActiveRecord::SchemaDumper
    module ActiveRecord
    class SchemaDumper
    def self.dump(connection, stream = STDOUT)
    connection.create_schema_dumper.dump(stream)
    end
    def dump(stream)
    header(stream)
    extensions(stream)
    tables(stream)
    trailer(stream)
    end
    end
    end
    @derekprior
    

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94. module ActiveRecord
    class SchemaDumper
    def self.dump(connection, stream = STDOUT)
    connection.create_schema_dumper.dump(stream)
    end
    def dump(stream)
    header(stream)
    extensions(stream)
    tables(stream)
    trailer(stream)
    end
    end
    end
    @derekprior
    

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95. module ActiveRecord
    class SchemaDumper
    def self.dump(connection, stream = STDOUT)
    connection.create_schema_dumper.dump(stream)
    end
    def dump(stream)
    header(stream)
    extensions(stream)
    tables(stream)
    trailer(stream)
    end
    end
    end
    @derekprior
    

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96. # This file is auto-generated from the current state of the database.
    # ...
    ActiveRecord::Schema.define(version: 2018_03_27_012835) do
    enable_extension "plpgsql"
    create_table "posts", force: :cascade do |t|
    t.string "title", null: false
    #...
    end
    create_table "users", force: :cascade do |t|
    t.string "email", null: false
    #...
    end
    add_foreign_key "posts", "users"
    end
    @derekprior
    

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97. # This file is auto-generated from the current state of the database.
    # ...
    ActiveRecord::Schema.define(version: 2018_03_27_012835) do
    enable_extension "plpgsql"
    create_table "posts", force: :cascade do |t|
    t.string "title", null: false
    #...
    end
    create_table "users", force: :cascade do |t|
    t.string "email", null: false
    #...
    end
    add_foreign_key "posts", "users"
    end
    @derekprior
    

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98. # This file is auto-generated from the current state of the database.
    # ...
    ActiveRecord::Schema.define(version: 2018_03_27_012835) do
    enable_extension "plpgsql"
    create_table "posts", force: :cascade do |t|
    t.string "title", null: false
    #...
    end
    create_table "users", force: :cascade do |t|
    t.string "email", null: false
    #...
    end
    add_foreign_key "posts", "users"
    end
    @derekprior
    

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99. # This file is auto-generated from the current state of the database.
    # ...
    ActiveRecord::Schema.define(version: 2018_03_27_012835) do
    enable_extension "plpgsql"
    create_table "posts", force: :cascade do |t|
    t.string "title", null: false
    #...
    end
    create_table "users", force: :cascade do |t|
    t.string "email", null: false
    #...
    end
    add_foreign_key "posts", "users"
    end
    @derekprior
    

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100. # This file is auto-generated from the current state of the database.
     # ...
     ActiveRecord::Schema.define(version: 2018_03_27_012835) do
     enable_extension "plpgsql"
     create_table "posts", force: :cascade do |t|
     t.string "title", null: false
     #...
     end
     create_table "users", force: :cascade do |t|
     t.string "email", null: false
     #...
     end
     add_foreign_key "posts", "users"
     end
     @derekprior
     

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101. # This file is auto-generated from the current state of the database.
     # ...
     ActiveRecord::Schema.define(version: 2018_03_27_012835) do
     enable_extension "plpgsql"
     create_table "posts", force: :cascade do |t|
     t.string "title", null: false
     #...
     end
     create_table "users", force: :cascade do |t|
     t.string "email", null: false
     #...
     end
     add_foreign_key "posts", "users"
     end
     @derekprior
     

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102. Justifies Its Existence
     # This file is auto-generated from the current state of the database. Instead
     # of editing this file, please use the migrations feature of Active Record to
     # incrementally modify your database, and then regenerate this schema definition.
     #
     # Note that this schema.rb definition is the authoritative source for your
     # database schema. If you need to create the application database on another
     # system, you should be using db:schema:load, not running all the migrations
     # from scratch. The latter is a flawed and unsustainable approach (the more migrations
     # you'll amass, the slower it'll run and the greater likelihood for issues).
     #
     # It's strongly recommended that you check this file into your version control system.
     @derekprior
     

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103. "... the authoritative
     source for your database
     schema"
     @derekprior
     

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104. !
     @derekprior
     

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105. "... you should be using
     db:schema:load, not
     running all migrations
     from scratch"
     @derekprior
     

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106. "the latter is a flawed and
     unsustainable approach"
     @derekprior
     

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107. "The more migrations you
     amass, the slower it'll run
     and the greater
     likelihood for issues"
     @derekprior
     

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108. !
     @derekprior
     

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109. !
     @derekprior
     

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110. ❌
     @derekprior
     

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111. "greater likelihood for
     issues..."
     @derekprior
     

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112. Causes of Migration Rot
     @derekprior
     

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113. Causes of Migration Rot
     → Changing schema statements over time
     @derekprior
     

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114. Causes of Migration Rot
     → Changing schema statements over time
     → External dependencies in migrations
     @derekprior
     

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115. Causes of Migration Rot
     → Changing schema statements over time
     → External dependencies in migrations
     @derekprior
     

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116. External Dependencies in Migrations
     class CombineNameFields < ActiveRecord::Migration[5.2]
     def change
     add_column :users, :name, :string
     reversible do |dir|
     dir.up do
     User.find_each { |u| u.update(name: "#{u.first_name} #{u.last_name}") }
     end
     end
     remove_column :users, :first_name, :string
     remove_column :users, :last_name, :string
     end
     end
     @derekprior
     

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117. External Dependencies in Migrations
     class CombineNameFields < ActiveRecord::Migration[5.2]
     def change
     add_column :users, :name, :string
     reversible do |dir|
     dir.up do
     User.find_each { |u| u.update(name: "#{u.first_name} #{u.last_name}") }
     end
     end
     remove_column :users, :first_name, :string
     remove_column :users, :last_name, :string
     end
     end
     @derekprior
     

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118. External Dependencies in Migrations
     class CombineNameFields < ActiveRecord::Migration[5.2]
     def change
     add_column :users, :name, :string
     execute "UPDATE users SET name = CONCAT(first_name, ' ', last_name)"
     remove_column :users, :first_name, :string
     remove_column :users, :last_name, :string
     end
     end
     @derekprior
     

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119. Mind Your
     Dependencies
     @derekprior
     

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120. Agenda
     → Anatomy of a Migration
     → Applying and Reverting a Migration
     → Schema Dumping
     → Shortcomings and Extensions
     @derekprior
     

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121. Shortcomings
     @derekprior
     

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122. Shortcomings
     → Migration rot
     @derekprior
     

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123. Shortcomings
     → Migration rot
     → Further removed from SQL
     @derekprior
     

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124. Shortcomings
     → Migration rot
     → Further removed from SQL
     → Support for a limited subset of features
     @derekprior
     

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125. Foreign Keys
     @derekprior
     

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126. Rails 4.2
     @derekprior
     

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127. Expression
     Indexes
     @derekprior
     

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128. Rails 5.0
     @derekprior
     

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129. Functions
     @derekprior
     

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130. !
     @derekprior
     

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131. Triggers
     @derekprior
     

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132. ☹
     @derekprior
     

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133. Views
     @derekprior
     

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134. !
     @derekprior
     

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135. execute "WHATEVER SQL YOU WANT"
     @derekprior
     

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136. config.active_record.schema_format = :sql
     @derekprior
     

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137. Extending
     Migrations
     @derekprior
     

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138. No Official API
     @derekprior
     

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139. !
     @derekprior
     

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140. !
     @derekprior
     

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141. Database
     Views
     @derekprior
     

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142. Requirements
     @derekprior
     

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143. Requirements
     → Schema Statements
     @derekprior
     

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144. Requirements
     → Schema Statements
     → Command Recorder
     @derekprior
     

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145. Requirements
     → Schema Statements
     → Command Recorder
     → Schema Dumper
     @derekprior
     

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146. Schema Statements
     module Scenic
     module Statements
     def create_view(version:, materialized: false)
     end
     def drop_view(version:, revert_to_version: nil, materialized: false)
     end
     def update_view(name, version:, revert_to_version: nil, materialized: false)
     end
     end
     end
     @derekprior
     

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147. Requirements
     → Schema Statements
     → Command Recorder
     → Schema Dumper
     @derekprior
     

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148. Command Recorder
     module Scenic
     module CommandRecorder
     def create_view(*args)
     record(:create_view, args)
     end
     def drop_view(*args)
     record(:drop_view, args)
     end
     def update_view(*args)
     record(:update_view, args)
     end
     end
     end
     @derekprior
     

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149. Command Recorder
     module Scenic
     module CommandRecorder
     def invert_create_view(args)
     [:drop_view, args]
     end
     def invert_drop_view(args)
     perform_scenic_inversion(:create_view, args)
     end
     def invert_update_view(args)
     perform_scenic_inversion(:update_view, args)
     end
     end
     end
     @derekprior
     

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150. Command Recorder
     module Scenic
     module CommandRecorder
     def perform_scenic_inversion(method, args)
     scenic_args = StatementArguments.new(args)
     if scenic_args.revert_to_version.nil?
     message = "#{method} is reversible only if given a revert_to_version"
     raise ActiveRecord::IrreversibleMigration, message
     end
     [method, scenic_args.invert_version.to_a]
     end
     end
     end
     @derekprior
     

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151. Requirements
     → Schema Statements
     → Command Recorder
     → Schema Dumper
     @derekprior
     

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152. Schema Dumper
     module Scenic
     module SchemaDumper
     def tables(stream)
     super
     views(stream)
     end
     def views
     # ...
     end
     end
     end
     @derekprior
     

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153. Schema Dumper
     module Scenic
     module SchemaDumper
     def tables(stream)
     super
     views(stream)
     end
     def views
     # ...
     end
     end
     end
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154. Wiring It All Up
     module Scenic
     class Railtie < Rails::Railtie
     initializer "scenic.load" do
     ActiveSupport.on_load :active_record do
     Scenic.load
     end
     end
     end
     def self.load
     ActiveRecord::ConnectionAdapters::AbstractAdapter.include Scenic::Statements
     ActiveRecord::Migration::CommandRecorder.include Scenic::CommandRecorder
     ActiveRecord::SchemaDumper.prepend Scenic::SchemaDumper
     end
     end
     @derekprior
     

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155. Wiring It All Up
     module Scenic
     class Railtie < Rails::Railtie
     initializer "scenic.load" do
     ActiveSupport.on_load :active_record do
     Scenic.load
     end
     end
     end
     def self.load
     ActiveRecord::ConnectionAdapters::AbstractAdapter.include Scenic::Statements
     ActiveRecord::Migration::CommandRecorder.include Scenic::CommandRecorder
     ActiveRecord::SchemaDumper.prepend Scenic::SchemaDumper
     end
     end
     @derekprior
     

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156. !
     @derekprior
     

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157. It's ALIVE!
     class UpdateSearchResults < ActiveRecord::Migration[5.2]
     def change
     update_view :search_results, version: 3, revert_to_version: 2
     end
     end
     @derekprior
     

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158. !
     @derekprior
     

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159. !
     @derekprior
     

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160. !
     @derekprior
     

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161. What if we did none of this?
     -- Some guy on a podcast
     @derekprior
     

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162. SQL
     Migrations
     @derekprior
     

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163. SQL Migrations
     db/migrate
     ├── 20180327005927_create_users
     │ ├── down.sql
     │ └── up.sql
     └── 20180327012835_create_posts
     ├── down.sql
     └── up.sql
     @derekprior
     

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164. @derekprior
     

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165. Pareto
     Principle
     @derekprior
     

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166. for many events, roughly
     80% of the effects come
     from 20% of the causes
     @derekprior
     

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167. Higher Level
     Abstraction
     @derekprior
     

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168. Ruby
     Migrations
     @derekprior
     

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169. !
     @derekprior
     

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170. !
     Maybe learn to love structure.sql
     

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171. Thank You
     Derek Prior
     → twitter: @derekprior
     → email: derek@thoughtbot.com
     → podcast: http://bikeshed.fm
     

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