model_schema.rb

module ActiveRecord
  module ModelSchema
    extend ActiveSupport::Concern

    included do
      ##
      # :singleton-method:
      # Accessor for the prefix type that will be prepended to every primary key column name.
      # The options are :table_name and :table_name_with_underscore. If the first is specified,
      # the Product class will look for "productid" instead of "id" as the primary column. If the
      # latter is specified, the Product class will look for "product_id" instead of "id". Remember
      # that this is a global setting for all Active Records.
      mattr_accessor :primary_key_prefix_type, instance_writer: false

      ##
      # :singleton-method:
      # Accessor for the name of the prefix string to prepend to every table name. So if set
      # to "basecamp_", all table names will be named like "basecamp_projects", "basecamp_people",
      # etc. This is a convenient way of creating a namespace for tables in a shared database.
      # By default, the prefix is the empty string.
      #
      # If you are organising your models within modules you can add a prefix to the models within
      # a namespace by defining a singleton method in the parent module called table_name_prefix which
      # returns your chosen prefix.
      class_attribute :table_name_prefix, instance_writer: false
      self.table_name_prefix = ""

      ##
      # :singleton-method:
      # Works like +table_name_prefix+, but appends instead of prepends (set to "_basecamp" gives "projects_basecamp",
      # "people_basecamp"). By default, the suffix is the empty string.
      #
      # If you are organising your models within modules, you can add a suffix to the models within
      # a namespace by defining a singleton method in the parent module called table_name_suffix which
      # returns your chosen suffix.
      class_attribute :table_name_suffix, instance_writer: false
      self.table_name_suffix = ""

      ##
      # :singleton-method:
      # Accessor for the name of the schema migrations table. By default, the value is "schema_migrations"
      class_attribute :schema_migrations_table_name, instance_accessor: false
      self.schema_migrations_table_name = "schema_migrations"

      ##
      # :singleton-method:
      # Accessor for the name of the internal metadata table. By default, the value is "ar_internal_metadata"
      class_attribute :internal_metadata_table_name, instance_accessor: false
      self.internal_metadata_table_name = "ar_internal_metadata"

      ##
      # :singleton-method:
      # Accessor for an array of names of environments where destructive actions should be prohibited. By default,
      # the value is ["production"]
      class_attribute :protected_environments, instance_accessor: false
      self.protected_environments = ["production"]

      ##
      # :singleton-method:
      # Indicates whether table names should be the pluralized versions of the corresponding class names.
      # If true, the default table name for a Product class will be +products+. If false, it would just be +product+.
      # See table_name for the full rules on table/class naming. This is true, by default.
      class_attribute :pluralize_table_names, instance_writer: false
      self.pluralize_table_names = true

      ##
      # :singleton-method:
      # Accessor for the list of columns names the model should ignore. Ignored columns won't have attribute
      # accessors defined, and won't be referenced in SQL queries.
      class_attribute :ignored_columns, instance_accessor: false
      self.ignored_columns = [].freeze

      self.inheritance_column = 'type'

      delegate :type_for_attribute, to: :class
    end

    # Derives the join table name for +first_table+ and +second_table+. The
    # table names appear in alphabetical order. A common prefix is removed
    # (useful for namespaced models like Music::Artist and Music::Record):
    #
    #   artists, records => artists_records
    #   records, artists => artists_records
    #   music_artists, music_records => music_artists_records
    def self.derive_join_table_name(first_table, second_table) # :nodoc:
      [first_table.to_s, second_table.to_s].sort.join("\0").gsub(/^(.*_)(.+)\0\1(.+)/, '\1\2_\3').tr("\0", "_")
    end

    module ClassMethods
      # Guesses the table name (in forced lower-case) based on the name of the class in the
      # inheritance hierarchy descending directly from ActiveRecord::Base. So if the hierarchy
      # looks like: Reply < Message < ActiveRecord::Base, then Message is used
      # to guess the table name even when called on Reply. The rules used to do the guess
      # are handled by the Inflector class in Active Support, which knows almost all common
      # English inflections. You can add new inflections in config/initializers/inflections.rb.
      #
      # Nested classes are given table names prefixed by the singular form of
      # the parent's table name. Enclosing modules are not considered.
      #
      # ==== Examples
      #
      #   class Invoice < ActiveRecord::Base
      #   end
      #
      #   file                  class               table_name
      #   invoice.rb            Invoice             invoices
      #
      #   class Invoice < ActiveRecord::Base
      #     class Lineitem < ActiveRecord::Base
      #     end
      #   end
      #
      #   file                  class               table_name
      #   invoice.rb            Invoice::Lineitem   invoice_lineitems
      #
      #   module Invoice
      #     class Lineitem < ActiveRecord::Base
      #     end
      #   end
      #
      #   file                  class               table_name
      #   invoice/lineitem.rb   Invoice::Lineitem   lineitems
      #
      # Additionally, the class-level +table_name_prefix+ is prepended and the
      # +table_name_suffix+ is appended. So if you have "myapp_" as a prefix,
      # the table name guess for an Invoice class becomes "myapp_invoices".
      # Invoice::Lineitem becomes "myapp_invoice_lineitems".
      #
      # You can also set your own table name explicitly:
      #
      #   class Mouse < ActiveRecord::Base
      #     self.table_name = "mice"
      #   end
      def table_name
        reset_table_name unless defined?(@table_name)
        @table_name
      end

      # Sets the table name explicitly. Example:
      #
      #   class Project < ActiveRecord::Base
      #     self.table_name = "project"
      #   end
      def table_name=(value)
        value = value && value.to_s

        if defined?(@table_name)
          return if value == @table_name
          reset_column_information if connected?
        end

        @table_name        = value
        @quoted_table_name = nil
        @arel_table        = nil
        @sequence_name     = nil unless defined?(@explicit_sequence_name) && @explicit_sequence_name
        @predicate_builder = nil
      end

      # Returns a quoted version of the table name, used to construct SQL statements.
      def quoted_table_name
        @quoted_table_name ||= connection.quote_table_name(table_name)
      end

      # Computes the table name, (re)sets it internally, and returns it.
      def reset_table_name #:nodoc:
        self.table_name = if abstract_class?
          superclass == Base ? nil : superclass.table_name
        elsif superclass.abstract_class?
          superclass.table_name || compute_table_name
        else
          compute_table_name
        end
      end

      def full_table_name_prefix #:nodoc:
        (parents.detect{ |p| p.respond_to?(:table_name_prefix) } || self).table_name_prefix
      end

      def full_table_name_suffix #:nodoc:
        (parents.detect {|p| p.respond_to?(:table_name_suffix) } || self).table_name_suffix
      end

      # Defines the name of the table column which will store the class name on single-table
      # inheritance situations.
      #
      # The default inheritance column name is +type+, which means it's a
      # reserved word inside Active Record. To be able to use single-table
      # inheritance with another column name, or to use the column +type+ in
      # your own model for something else, you can set +inheritance_column+:
      #
      #     self.inheritance_column = 'zoink'
      def inheritance_column
        (@inheritance_column ||= nil) || superclass.inheritance_column
      end

      # Sets the value of inheritance_column
      def inheritance_column=(value)
        @inheritance_column = value.to_s
        @explicit_inheritance_column = true
      end

      def sequence_name
        if base_class == self
          @sequence_name ||= reset_sequence_name
        else
          (@sequence_name ||= nil) || base_class.sequence_name
        end
      end

      def reset_sequence_name #:nodoc:
        @explicit_sequence_name = false
        @sequence_name          = connection.default_sequence_name(table_name, primary_key)
      end

      # Sets the name of the sequence to use when generating ids to the given
      # value, or (if the value is nil or false) to the value returned by the
      # given block. This is required for Oracle and is useful for any
      # database which relies on sequences for primary key generation.
      #
      # If a sequence name is not explicitly set when using Oracle,
      # it will default to the commonly used pattern of: #{table_name}_seq
      #
      # If a sequence name is not explicitly set when using PostgreSQL, it
      # will discover the sequence corresponding to your primary key for you.
      #
      #   class Project < ActiveRecord::Base
      #     self.sequence_name = "projectseq"   # default would have been "project_seq"
      #   end
      def sequence_name=(value)
        @sequence_name          = value.to_s
        @explicit_sequence_name = true
      end

      # Determines if the primary key values should be selected from their
      # corresponding sequence before the insert statement.
      def prefetch_primary_key?
        connection.prefetch_primary_key?(table_name)
      end

      # Returns the next value that will be used as the primary key on
      # an insert statement.
      def next_sequence_value
        connection.next_sequence_value(sequence_name)
      end

      # Indicates whether the table associated with this class exists
      def table_exists?
        connection.schema_cache.data_source_exists?(table_name)
      end

      def attributes_builder # :nodoc:
        @attributes_builder ||= AttributeSet::Builder.new(attribute_types, primary_key)
      end

      def columns_hash # :nodoc:
        load_schema
        @columns_hash
      end

      def columns
        load_schema
        @columns ||= columns_hash.values
      end

      def attribute_types # :nodoc:
        load_schema
        @attribute_types ||= Hash.new(Type::Value.new)
      end

      # Returns the type of the attribute with the given name, after applying
      # all modifiers. This method is the only valid source of information for
      # anything related to the types of a model's attributes. This method will
      # access the database and load the model's schema if it is required.
      #
      # The return value of this method will implement the interface described
      # by ActiveModel::Type::Value (though the object itself may not subclass
      # it).
      #
      # +attr_name+ The name of the attribute to retrieve the type for. Must be
      # a string
      def type_for_attribute(attr_name)
        attribute_types[attr_name]
      end

      # Returns a hash where the keys are column names and the values are
      # default values when instantiating the Active Record object for this table.
      def column_defaults
        load_schema
        _default_attributes.to_hash
      end

      def _default_attributes # :nodoc:
        @default_attributes ||= AttributeSet.new({})
      end

      # Returns an array of column names as strings.
      def column_names
        @column_names ||= columns.map(&:name)
      end

      # Returns an array of column objects where the primary id, all columns ending in "_id" or "_count",
      # and columns used for single table inheritance have been removed.
      def content_columns
        @content_columns ||= columns.reject { |c| c.name == primary_key || c.name =~ /(_id|_count)$/ || c.name == inheritance_column }
      end

      # Resets all the cached information about columns, which will cause them
      # to be reloaded on the next request.
      #
      # The most common usage pattern for this method is probably in a migration,
      # when just after creating a table you want to populate it with some default
      # values, eg:
      #
      #  class CreateJobLevels < ActiveRecord::Migration[5.0]
      #    def up
      #      create_table :job_levels do |t|
      #        t.integer :id
      #        t.string :name
      #
      #        t.timestamps
      #      end
      #
      #      JobLevel.reset_column_information
      #      %w{assistant executive manager director}.each do |type|
      #        JobLevel.create(name: type)
      #      end
      #    end
      #
      #    def down
      #      drop_table :job_levels
      #    end
      #  end
      def reset_column_information
        connection.clear_cache!
        undefine_attribute_methods
        connection.schema_cache.clear_data_source_cache!(table_name)

        reload_schema_from_cache
      end

      private

      def schema_loaded?
        defined?(@columns_hash) && @columns_hash
      end

      def load_schema
        unless schema_loaded?
          load_schema!
        end
      end

      def load_schema!
        @columns_hash = connection.schema_cache.columns_hash(table_name).except(*ignored_columns)
        @columns_hash.each do |name, column|
          warn_if_deprecated_type(column)
          define_attribute(
            name,
            connection.lookup_cast_type_from_column(column),
            default: column.default,
            user_provided_default: false
          )
        end
      end

      def reload_schema_from_cache
        @arel_engine = nil
        @arel_table = nil
        @column_names = nil
        @attribute_types = nil
        @content_columns = nil
        @default_attributes = nil
        @inheritance_column = nil unless defined?(@explicit_inheritance_column) && @explicit_inheritance_column
        @attributes_builder = nil
        @columns = nil
        @columns_hash = nil
        @attribute_names = nil
        direct_descendants.each do |descendant|
          descendant.send(:reload_schema_from_cache)
        end
      end

      # Guesses the table name, but does not decorate it with prefix and suffix information.
      def undecorated_table_name(class_name = base_class.name)
        table_name = class_name.to_s.demodulize.underscore
        pluralize_table_names ? table_name.pluralize : table_name
      end

      # Computes and returns a table name according to default conventions.
      def compute_table_name
        base = base_class
        if self == base
          # Nested classes are prefixed with singular parent table name.
          if parent < Base && !parent.abstract_class?
            contained = parent.table_name
            contained = contained.singularize if parent.pluralize_table_names
            contained += '_'
          end

          "#{full_table_name_prefix}#{contained}#{undecorated_table_name(name)}#{full_table_name_suffix}"
        else
          # STI subclasses always use their superclass' table.
          base.table_name
        end
      end

      def warn_if_deprecated_type(column)
        return if attributes_to_define_after_schema_loads.key?(column.name)
        if column.respond_to?(:oid) && column.sql_type.start_with?("point")
          if column.array?
            array_arguments = ", array: true"
          else
            array_arguments = ""
          end
          ActiveSupport::Deprecation.warn(<<-WARNING.strip_heredoc)
            The behavior of the `:point` type will be changing in Rails 5.1 to
            return a `Point` object, rather than an `Array`. If you'd like to
            keep the old behavior, you can add this line to #{self.name}:

              attribute :#{column.name}, :legacy_point#{array_arguments}

            If you'd like the new behavior today, you can add this line:

              attribute :#{column.name}, :point#{array_arguments}
          WARNING
        end
      end
    end
  end
end