Method: ActiveRecord::PGExtensions::PessimisticMigrations#change_column_null

Defined in:
lib/active_record/pg_extensions/pessimistic_migrations.rb

#change_column_null(table, column, nullness, default = nil) ⇒ Object

adds a temporary check constraint to reduce locking when changing to NOT NULL, and we’re not in a transaction



10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
 
# File 'lib/active_record/pg_extensions/pessimistic_migrations.rb', line 10

def change_column_null(table, column, nullness, default = nil)
  # no point in doing extra work to avoid locking if we're already in a transaction
  return super if nullness != false || open_transactions.positive?
  return if columns(table).find { |c| c.name == column.to_s }&.null == false

  # PG identifiers max out at 63 characters
  temp_constraint_name = "chk_rails_#{table}_#{column}_not_null"[0...63]
  scope = quoted_scope(temp_constraint_name)
  # check for temp constraint
  valid = select_value("    SELECT convalidated FROM pg_constraint INNER JOIN pg_namespace ON pg_namespace.oid=connamespace WHERE conname=\#{scope[:name]} AND nspname=\#{scope[:schema]}\n  SQL\n  if valid.nil?\n    add_check_constraint(table,\n                         \"\#{quote_column_name(column)} IS NOT NULL\",\n                         name: temp_constraint_name,\n                         validate: false)\n  end\n  begin\n    validate_constraint(table, temp_constraint_name)\n  rescue PG::CheckViolation => e\n    raise ActiveRecord::NotNullViolation.new(sql: e.sql, binds: e.binds)\n  end\n\n  transaction do\n    super\n    remove_check_constraint(table, name: temp_constraint_name)\n  end\nend\n", "SCHEMA")