module ActiveRecord::ModelSchema::ClassMethods

# File lib/active_record/model_schema.rb, line 488
def column_defaults
  load_schema
  @column_defaults ||= _default_attributes.deep_dup.to_hash.freeze
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.

# File lib/active_record/model_schema.rb, line 479
def column_for_attribute(name)
  name = name.to_s
  columns_hash.fetch(name) do
    ConnectionAdapters::NullColumn.new(name)
  end
end

Returns the column object for the named attribute. Returns an ActiveRecord::ConnectionAdapters::NullColumn if the named attribute does not exist.

class Person < ActiveRecord::Base
end

person = Person.new
person.column_for_attribute(:name) # the result depends on the ConnectionAdapter
# => #<ActiveRecord::ConnectionAdapters::Column:0x007ff4ab083980 @name="name", @sql_type="varchar(255)", @null=true, ...>

person.column_for_attribute(:nothing)
# => #<ActiveRecord::ConnectionAdapters::NullColumn:0xXXX @name=nil, @sql_type=nil, @cast_type=#<Type::Value>, ...>

# File lib/active_record/model_schema.rb, line 494
def column_names
  @column_names ||= columns.map(&:name).freeze
end

Returns an array of column names as strings.

# File lib/active_record/model_schema.rb, line 505
def content_columns
  @content_columns ||= columns.reject do |c|
    c.name == primary_key ||
    c.name == inheritance_column ||
    c.name.end_with?("_id", "_count")
  end.freeze
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.

# File lib/active_record/model_schema.rb, line 334
def ignored_columns
  @ignored_columns || superclass.ignored_columns
end

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.

# File lib/active_record/model_schema.rb, line 375
def ignored_columns=(columns)
  check_model_columns(@only_columns.present?)
  reload_schema_from_cache
  @ignored_columns = columns.map(&:to_s).freeze
end

Sets the columns names the model should ignore. Ignored columns won’t have attribute accessors defined, and won’t be referenced in SQL queries.

A common usage pattern for this method is to ensure all references to an attribute have been removed and deployed, before a migration to drop the column from the database has been deployed and run. Using this two step approach to dropping columns ensures there is no code that raises errors due to having a cached schema in memory at the time the schema migration is run.

For example, given a model where you want to drop the “category” attribute, first mark it as ignored:

class Project < ActiveRecord::Base
  # schema:
  #   id         :bigint
  #   name       :string, limit: 255
  #   category   :string, limit: 255

  self.ignored_columns += [:category]
end

The schema still contains “category”, but now the model omits it, so any meta-driven code or schema caching will not attempt to use the column:

Project.columns_hash["category"] => nil

You will get an error if accessing that attribute directly, so ensure all usages of the column are removed (automated tests can help you find any usages).

user = Project.create!(name: "First Project")
user.category # => raises NoMethodError

# File lib/active_record/model_schema.rb, line 550
def load_schema
  return if schema_loaded?
  @load_schema_monitor.synchronize do
    return if schema_loaded?

    load_schema!

    @schema_loaded = true
  rescue
    reload_schema_from_cache # If the schema loading failed half way through, we must reset the state.
    raise
  end
end

Load the model’s schema information either from the schema cache or directly from the database.

# File lib/active_record/model_schema.rb, line 427
def next_sequence_value
  with_connection { |c| c.next_sequence_value(sequence_name) }
end

Returns the next value that will be used as the primary key on an insert statement.

# File lib/active_record/model_schema.rb, line 340
def only_columns
  @only_columns || superclass.only_columns
end

The list of columns names the model should allow. Only columns are used to define attribute accessors, and are referenced in SQL queries.

# File lib/active_record/model_schema.rb, line 421
def prefetch_primary_key?
  with_connection { |c| c.prefetch_primary_key?(table_name) }
end

Determines if the primary key values should be selected from their corresponding sequence before the insert statement.

# File lib/active_record/model_schema.rb, line 315
def protected_environments
  if defined?(@protected_environments)
    @protected_environments
  else
    superclass.protected_environments
  end
end

The array of names of environments where destructive actions should be prohibited. By default, the value is ["production"].

# File lib/active_record/model_schema.rb, line 324
def protected_environments=(environments)
  @protected_environments = environments.map(&:to_s)
end

Sets an array of names of environments where destructive actions should be prohibited.

# File lib/active_record/model_schema.rb, line 288
def quoted_table_name
  adapter_class.quote_table_name(table_name)
end

Returns a quoted version of the table name.

# File lib/active_record/model_schema.rb, line 539
def reset_column_information
  connection_pool.active_connection&.clear_cache!
  ([self] + descendants).each(&:undefine_attribute_methods)
  schema_cache.clear_data_source_cache!(table_name)

  reload_schema_from_cache
  initialize_find_by_cache
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, e.g.:

class CreateJobLevels < ActiveRecord::Migration[8.1]
  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

# File lib/active_record/model_schema.rb, line 414
def sequence_name=(value)
  @sequence_name          = value.to_s
  @explicit_sequence_name = true
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

# File lib/active_record/model_schema.rb, line 432
def table_exists?
  schema_cache.data_source_exists?(table_name)
end

Indicates whether the table associated with this class exists

# File lib/active_record/model_schema.rb, line 263
def table_name
  reset_table_name unless defined?(@table_name)
  @table_name
end

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”.

Active Model Naming’s model_name is the base name used to guess the table name. In case a custom Active Model Name is defined, it will be used for the table name as well:

class PostRecord < ActiveRecord::Base
  class << self
    def model_name
      ActiveModel::Name.new(self, nil, "Post")
    end
  end
end

PostRecord.table_name
# => "posts"

You can also set your own table name explicitly:

class Mouse < ActiveRecord::Base
  self.table_name = "mice"
end

# File lib/active_record/model_schema.rb, line 273
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
  @arel_table        = nil
  @sequence_name     = nil unless @explicit_sequence_name
  @predicate_builder = nil
end

Sets the table name explicitly. Example:

class Project < ActiveRecord::Base
  self.table_name = "project"
end