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ParameterFilter allows you to specify keys for sensitive data from hash-like object and replace corresponding value. Filtering only certain sub-keys from a hash is possible by using the dot notation: 'credit_card.number'. If a proc is given, each key and value of a hash and all sub-hashes are passed to it, where the value or the key can be replaced using String#replace or similar methods.[:password])
=> replaces the value to all keys matching /password/i with "[FILTERED]"[:foo, "bar"])
=> replaces the value to all keys matching /foo|bar/i with "[FILTERED]"[/\Apin\z/i, /\Apin_/i])
=> replaces the value for the exact (case-insensitive) key 'pin' and all
(case-insensitive) keys beginning with 'pin_', with "[FILTERED]".
Does not match keys with 'pin' as a substring, such as 'shipping_id'.["credit_card.code"])
=> replaces { credit_card: {code: "xxxx"} } with "[FILTERED]", does not
change { file: { code: "xxxx"} }[-> (k, v) do
  v.reverse! if /secret/i.match?(k)
=> reverses the value to all keys matching /secret/i

Class Public methods

new(filters = [], mask: FILTERED)

Create instance with given filters. Supported type of filters are String, Regexp, and Proc. Other types of filters are treated as String using to_s. For Proc filters, key, value, and optional original hash is passed to block arguments.


  • :mask - A replaced object when filtered. Defaults to "[FILTERED]".

# File activesupport/lib/active_support/parameter_filter.rb, line 71
def initialize(filters = [], mask: FILTERED)
  @mask = mask


Precompiles an array of filters that otherwise would be passed directly to initialize. Depending on the quantity and types of filters, precompilation can improve filtering performance, especially in the case where the ParameterFilter instance itself cannot be retained (but the precompiled filters can be retained).

filters = [/foo/, :bar, "nested.baz", /nested\.qux/]

precompiled = ActiveSupport::ParameterFilter.precompile_filters(filters)
# => [/(?-mix:foo)|(?i:bar)/, /(?i:nested\.baz)|(?-mix:nested\.qux)/]
# File activesupport/lib/active_support/parameter_filter.rb, line 49
def self.precompile_filters(filters)
  filters, patterns = filters.partition { |filter| filter.is_a?(Proc) }! do |pattern|
    pattern.is_a?(Regexp) ? pattern : "(?i:#{Regexp.escape pattern.to_s})"

  deep_patterns = patterns.extract! { |pattern| pattern.to_s.include?("\\.") }

  filters <<"|")) if patterns.any?
  filters <<"|")) if deep_patterns.any?


Instance Public methods


Mask value of params if key matches one of filters.

# File activesupport/lib/active_support/parameter_filter.rb, line 77
def filter(params)
  @no_filters ? params.dup : call(params)

filter_param(key, value)

Returns filtered value for given key. For Proc filters, third block argument is not populated.

# File activesupport/lib/active_support/parameter_filter.rb, line 82
def filter_param(key, value)
  @no_filters ? value : value_for_key(key, value)