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ParameterFilter replaces values in a Hash-like object if their keys match one of the specified filters.

Matching based on nested keys is possible by using dot notation, e.g. "credit_card.number".

If a proc is given as a filter, each key and value of the Hash-like and of any nested Hashes will be passed to it. The value or key can then be mutated as desired using methods such as String#replace.

# Replaces values with "[FILTERED]" for keys that match /password/i.[:password])

# Replaces values with "[FILTERED]" for keys that match /foo|bar/i.[:foo, "bar"])

# Replaces values for the exact key "pin" and for keys that begin with
# "pin_". Does not match keys that otherwise include "pin" as a
# substring, such as "shipping_id".[/\Apin\z/, /\Apin_/])

# Replaces the value for :code in `{ credit_card: { code: "xxxx" } }`.
# Does not change `{ file: { code: "xxxx" } }`.["credit_card.code"])

# Reverses values for keys that match /secret/i.[-> (k, v) do
  v.reverse! if /secret/i.match?(k)

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 46
def initialize(filters = [], mask: FILTERED)
  @filters = filters
  @mask = mask

Instance Public methods


Mask value of params if key matches one of filters.

# File activesupport/lib/active_support/parameter_filter.rb, line 52
def filter(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 57
def filter_param(key, value)
  @filters.empty? ? value : compiled_filter.value_for_key(key, value)