Set default :text type column limit

lib/default_settings_strategy.rb

@@ -1,18 +1,40 @@
 class DefaultSettingsStrategy < ActiveRecord::Migration::DefaultStrategy
-  # Without `:if_not_exists`/`:if_exists` options it's impossible to change
-  # migration status once migration fails partially. If `up` migration creates
-  # some, but not all objects, its status is not updated from `down` to `up`.
-  # Then it's impossible to migrate: a) up - due to `already exists` errors and
-  # b) down - due to migration status.
-  # Using `force: :cascade` does nothing on MySQL, so `force:` is useless.
-  # Adding `null: false` here somehow does not show up in schema files, be careful!
-  # TODO: add_foreign_key {on_delete: :cascade} ?
-  DEFAULTS = {
+  COLUMN_DEFAULTS = {
+    # TODO: all types `null: false` ?
+    # TODO: references `foreign_key: {on_delete: :cascade}` ?
+    # `timestamps` - Rails defaults to `null: false, precision: true`.
+    # `limit:` for `text` - `text` can be theoretically up to 1GB or
+    #   longer, so roughly unlimited for practical purposes. But:
+    #   * the actual usable length depends on additional factors, like compile
+    #     time limits (`SQLITE_MAX_LENGTH` in SQLite), runtime settings
+    #     (`max_allowed_packet` in MySQL) and probably other,
+    #   * Rails does not report limit for `text` column types, unless it is
+    #     explicitly set.
+    #   The decision is to always set safe limit and enforce it by validations, to
+    #   avoid surprises (e.g. text truncation) when saving to dabatase.
+    text: {limit: 2**16 - 1}
+  }
+  COLUMN_DEFAULTS.default = {}
+  COLUMN_DEFAULTS.freeze
+
+  module ColumnSettingsStrategy
+    def column(name, type, **options)
+      super(name, type, **COLUMN_DEFAULTS[type].merge(options))
+    end
+  end
+  ActiveRecord::ConnectionAdapters::TableDefinition.prepend ColumnSettingsStrategy
+
+  # `force: :cascade` - does nothing on MySQL, so `force:` is useless.
+  # `if_not_exists: true`/`if_exists: true` - without these options it's impossible
+  #   to change migration status once migration fails partially. If `up` migration
+  #   creates some, but not all objects, its status is not updated from `down` to
+  #   `up`. Then it's impossible to migrate: a) up - due to `already exists`
+  #   errors and b) down - due to migration status.
+  MIGRATION_DEFAULTS = {
     add_check_constraint: {if_not_exists: true},
     add_column:           {if_not_exists: true},
     add_foreign_key:      {if_not_exists: true},
     add_index:            {if_not_exists: true, unique: true},
-    # Timestamps are by default `null: false, precision: true`.
     add_timestamps:       {if_not_exists: true},
     create_table:         {if_not_exists: true},
     drop_table:               {if_exists: true},
@@ -22,11 +44,12 @@ class DefaultSettingsStrategy < ActiveRecord::Migration::DefaultStrategy
     remove_index:             {if_exists: true},
     remove_timestamps:        {if_exists: true},
   }
-  DEFAULTS.default = {}
-  DEFAULTS.freeze
+  MIGRATION_DEFAULTS.default = {}
+  MIGRATION_DEFAULTS.freeze
 
   def method_missing(method, *args, **kwargs, &)
     conflicts = kwargs.has_key?(:force) ? [:if_not_exists, :if_exists] : []
-    super(method, *args, **DEFAULTS[method.to_sym].except(*conflicts).merge(kwargs), &)
+    defaults = MIGRATION_DEFAULTS[method.to_sym].except(*conflicts)
+    super(method, *args, **defaults.merge(kwargs), &)
   end
 end