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Active Record Validations
This guide teaches you how to validate the state of objects before they go into the database using Active Record's validations feature.
After reading this guide, you will know:
- How to use the built-in Active Record validation helpers.
- How to create your own custom validation methods.
- How to work with the error messages generated by the validation process.
Validations Overview
Here's an example of a very simple validation:
class Person < ApplicationRecord
validates :name, presence: true
end
Person.create(name: "John Doe").valid? # => true
Person.create(name: nil).valid? # => false
As you can see, our validation lets us know that our Person is not valid
without a name attribute. The second Person will not be persisted to the
database.
Before we dig into more details, let's talk about how validations fit into the big picture of your application.
Why Use Validations?
Validations are used to ensure that only valid data is saved into your database. For example, it may be important to your application to ensure that every user provides a valid email address and mailing address. Model-level validations are the best way to ensure that only valid data is saved into your database. They are database agnostic, cannot be bypassed by end users, and are convenient to test and maintain. Rails provides built-in helpers for common needs, and allows you to create your own validation methods as well.
There are several other ways to validate data before it is saved into your database, including native database constraints, client-side validations and controller-level validations. Here's a summary of the pros and cons:
- Database constraints and/or stored procedures make the validation mechanisms database-dependent and can make testing and maintenance more difficult. However, if your database is used by other applications, it may be a good idea to use some constraints at the database level. Additionally, database-level validations can safely handle some things (such as uniqueness in heavily-used tables) that can be difficult to implement otherwise.
- Client-side validations can be useful, but are generally unreliable if used alone. If they are implemented using JavaScript, they may be bypassed if JavaScript is turned off in the user's browser. However, if combined with other techniques, client-side validation can be a convenient way to provide users with immediate feedback as they use your site.
- Controller-level validations can be tempting to use, but often become unwieldy and difficult to test and maintain. Whenever possible, it's a good idea to keep your controllers skinny, as it will make your application a pleasure to work within the long run.
Choose these in certain, specific cases. It's the opinion of the Rails team that model-level validations are the most appropriate in most circumstances.
When Does Validation Happen?
There are two kinds of Active Record objects: those that correspond to a row
inside your database and those that do not. When you create a fresh object, for
example using the new method, that object does not belong to the database
yet. Once you call save upon that object it will be saved into the
appropriate database table. Active Record uses the new_record? instance
method to determine whether an object is already in the database or not.
Consider the following Active Record class:
class Person < ApplicationRecord
end
We can see how it works by looking at some bin/rails console output:
>> p = Person.new(name: "John Doe")
=> #<Person id: nil, name: "John Doe", created_at: nil, updated_at: nil>
>> p.new_record?
=> true
>> p.save
=> true
>> p.new_record?
=> false
Creating and saving a new record will send an SQL INSERT operation to the
database. Updating an existing record will send an SQL UPDATE operation
instead. Validations are typically run before these commands are sent to the
database. If any validations fail, the object will be marked as invalid and
Active Record will not perform the INSERT or UPDATE operation. This avoids
storing an invalid object in the database. You can choose to have specific
validations run when an object is created, saved, or updated.
CAUTION: There are many ways to change the state of an object in the database. Some methods will trigger validations, but some will not. This means that it's possible to save an object in the database in an invalid state if you aren't careful.
The following methods trigger validations, and will save the object to the database only if the object is valid:
createcreate!savesave!updateupdate!
The bang versions (e.g. save!) raise an exception if the record is invalid.
The non-bang versions don't: save and update return false, and
create returns the object.
Skipping Validations
The following methods skip validations, and will save the object to the database regardless of its validity. They should be used with caution.
decrement!decrement_counterincrement!increment_counterinsertinsert!insert_allinsert_all!toggle!touchtouch_allupdate_allupdate_attributeupdate_columnupdate_columnsupdate_countersupsertupsert_all
Note that save also has the ability to skip validations if passed validate: false as an argument. This technique should be used with caution.
save(validate: false)
valid? and invalid?
Before saving an Active Record object, Rails runs your validations. If these validations produce any errors, Rails does not save the object.
You can also run these validations on your own. valid? triggers your validations
and returns true if no errors were found in the object, and false otherwise.
As you saw above:
class Person < ApplicationRecord
validates :name, presence: true
end
Person.create(name: "John Doe").valid? # => true
Person.create(name: nil).valid? # => false
After Active Record has performed validations, any errors found can be accessed
through the errors instance method, which returns a collection of errors.
By definition, an object is valid if this collection is empty after running
validations.
Note that an object instantiated with new will not report errors
even if it's technically invalid, because validations are automatically run
only when the object is saved, such as with the create or save methods.
class Person < ApplicationRecord
validates :name, presence: true
end
>> p = Person.new
# => #<Person id: nil, name: nil>
>> p.errors.size
# => 0
>> p.valid?
# => false
>> p.errors.objects.first.full_message
# => "Name can't be blank"
>> p = Person.create
# => #<Person id: nil, name: nil>
>> p.errors.objects.first.full_message
# => "Name can't be blank"
>> p.save
# => false
>> p.save!
# => ActiveRecord::RecordInvalid: Validation failed: Name can't be blank
>> Person.create!
# => ActiveRecord::RecordInvalid: Validation failed: Name can't be blank
invalid? is the inverse of valid?. It triggers your validations,
returning true if any errors were found in the object, and false otherwise.
errors[]
To verify whether or not a particular attribute of an object is valid, you can
use errors[:attribute]. It returns an array of all the error messages for
:attribute. If there are no errors on the specified attribute, an empty array
is returned.
This method is only useful after validations have been run, because it only
inspects the errors collection and does not trigger validations itself. It's
different from the ActiveRecord::Base#invalid? method explained above because
it doesn't verify the validity of the object as a whole. It only checks to see
whether there are errors found on an individual attribute of the object.
class Person < ApplicationRecord
validates :name, presence: true
end
>> Person.new.errors[:name].any? # => false
>> Person.create.errors[:name].any? # => true
We'll cover validation errors in greater depth in the Working with Validation Errors section.
Validation Helpers
Active Record offers many pre-defined validation helpers that you can use
directly inside your class definitions. These helpers provide common validation
rules. Every time a validation fails, an error is added to the object's
errors collection, and this is associated with the attribute being
validated.
Each helper accepts an arbitrary number of attribute names, so with a single line of code you can add the same kind of validation to several attributes.
All of them accept the :on and :message options, which define when the
validation should be run and what message should be added to the errors
collection if it fails, respectively. The :on option takes one of the values
:create or :update. There is a default error
message for each one of the validation helpers. These messages are used when
the :message option isn't specified. Let's take a look at each one of the
available helpers.
acceptance
This method validates that a checkbox on the user interface was checked when a form was submitted. This is typically used when the user needs to agree to your application's terms of service, confirm that some text is read, or any similar concept.
class Person < ApplicationRecord
validates :terms_of_service, acceptance: true
end
This check is performed only if terms_of_service is not nil.
The default error message for this helper is "must be accepted".
You can also pass in a custom message via the message option.
class Person < ApplicationRecord
validates :terms_of_service, acceptance: { message: 'must be abided' }
end
It can also receive an :accept option, which determines the allowed values
that will be considered as accepted. It defaults to ['1', true] and can be
easily changed.
class Person < ApplicationRecord
validates :terms_of_service, acceptance: { accept: 'yes' }
validates :eula, acceptance: { accept: ['TRUE', 'accepted'] }
end
This validation is very specific to web applications and this
'acceptance' does not need to be recorded anywhere in your database. If you
don't have a field for it, the helper will create a virtual attribute. If
the field does exist in your database, the accept option must be set to
or include true or else the validation will not run.
validates_associated
You should use this helper when your model has associations with other models
and they also need to be validated. When you try to save your object, valid?
will be called upon each one of the associated objects.
class Library < ApplicationRecord
has_many :books
validates_associated :books
end
This validation will work with all of the association types.
CAUTION: Don't use validates_associated on both ends of your associations.
They would call each other in an infinite loop.
The default error message for validates_associated is "is invalid". Note
that each associated object will contain its own errors collection; errors do
not bubble up to the calling model.
confirmation
You should use this helper when you have two text fields that should receive exactly the same content. For example, you may want to confirm an email address or a password. This validation creates a virtual attribute whose name is the name of the field that has to be confirmed with "_confirmation" appended.
class Person < ApplicationRecord
validates :email, confirmation: true
end
In your view template you could use something like
<%= text_field :person, :email %>
<%= text_field :person, :email_confirmation %>
This check is performed only if email_confirmation is not nil. To require
confirmation, make sure to add a presence check for the confirmation attribute
(we'll take a look at presence later on in this guide):
class Person < ApplicationRecord
validates :email, confirmation: true
validates :email_confirmation, presence: true
end
There is also a :case_sensitive option that you can use to define whether the
confirmation constraint will be case sensitive or not. This option defaults to
true.
class Person < ApplicationRecord
validates :email, confirmation: { case_sensitive: false }
end
The default error message for this helper is "doesn't match confirmation".
exclusion
This helper validates that the attributes' values are not included in a given set. In fact, this set can be any enumerable object.
class Account < ApplicationRecord
validates :subdomain, exclusion: { in: %w(www us ca jp),
message: "%{value} is reserved." }
end
The exclusion helper has an option :in that receives the set of values that
will not be accepted for the validated attributes. The :in option has an
alias called :within that you can use for the same purpose, if you'd like to.
This example uses the :message option to show how you can include the
attribute's value. For full options to the message argument please see the
message documentation.
The default error message is "is reserved".
format
This helper validates the attributes' values by testing whether they match a
given regular expression, which is specified using the :with option.
class Product < ApplicationRecord
validates :legacy_code, format: { with: /\A[a-zA-Z]+\z/,
message: "only allows letters" }
end
Alternatively, you can require that the specified attribute does not match the regular expression by using the :without option.
The default error message is "is invalid".
inclusion
This helper validates that the attributes' values are included in a given set. In fact, this set can be any enumerable object.
class Coffee < ApplicationRecord
validates :size, inclusion: { in: %w(small medium large),
message: "%{value} is not a valid size" }
end
The inclusion helper has an option :in that receives the set of values that
will be accepted. The :in option has an alias called :within that you can
use for the same purpose, if you'd like to. The previous example uses the
:message option to show how you can include the attribute's value. For full
options please see the message documentation.
The default error message for this helper is "is not included in the list".
length
This helper validates the length of the attributes' values. It provides a variety of options, so you can specify length constraints in different ways:
class Person < ApplicationRecord
validates :name, length: { minimum: 2 }
validates :bio, length: { maximum: 500 }
validates :password, length: { in: 6..20 }
validates :registration_number, length: { is: 6 }
end
The possible length constraint options are:
:minimum- The attribute cannot have less than the specified length.:maximum- The attribute cannot have more than the specified length.:in(or:within) - The attribute length must be included in a given interval. The value for this option must be a range.:is- The attribute length must be equal to the given value.
The default error messages depend on the type of length validation being
performed. You can personalize these messages using the :wrong_length,
:too_long, and :too_short options and %{count} as a placeholder for the
number corresponding to the length constraint being used. You can still use the
:message option to specify an error message.
class Person < ApplicationRecord
validates :bio, length: { maximum: 1000,
too_long: "%{count} characters is the maximum allowed" }
end
Note that the default error messages are plural (e.g., "is too short (minimum
is %{count} characters)"). For this reason, when :minimum is 1 you should
provide a personalized message or use presence: true instead. When
:in or :within have a lower limit of 1, you should either provide a
personalized message or call presence prior to length.
numericality
This helper validates that your attributes have only numeric values. By default, it will match an optional sign followed by an integral or floating point number.
To specify that only integral numbers are allowed,
set :only_integer to true. Then it will use the
/\A[+-]?\d+\z/
regular expression to validate the attribute's value. Otherwise, it will try to
convert the value to a number using Float. Floats are casted to BigDecimal using the column's precision value or 15.
class Player < ApplicationRecord
validates :points, numericality: true
validates :games_played, numericality: { only_integer: true }
end
The default error message for :only_integer is "must be an integer".
Besides :only_integer, this helper also accepts the following options to add
constraints to acceptable values:
:greater_than- Specifies the value must be greater than the supplied value. The default error message for this option is "must be greater than %{count}".:greater_than_or_equal_to- Specifies the value must be greater than or equal to the supplied value. The default error message for this option is "must be greater than or equal to %{count}".:equal_to- Specifies the value must be equal to the supplied value. The default error message for this option is "must be equal to %{count}".:less_than- Specifies the value must be less than the supplied value. The default error message for this option is "must be less than %{count}".:less_than_or_equal_to- Specifies the value must be less than or equal to the supplied value. The default error message for this option is "must be less than or equal to %{count}".:other_than- Specifies the value must be other than the supplied value. The default error message for this option is "must be other than %{count}".:odd- Specifies the value must be an odd number if set to true. The default error message for this option is "must be odd".:even- Specifies the value must be an even number if set to true. The default error message for this option is "must be even".
NOTE: By default, numericality doesn't allow nil values. You can use allow_nil: true option to permit it.
The default error message when no options are specified is "is not a number".
presence
This helper validates that the specified attributes are not empty. It uses the
blank? method to check if the value is either nil or a blank string, that
is, a string that is either empty or consists of whitespace.
class Person < ApplicationRecord
validates :name, :login, :email, presence: true
end
If you want to be sure that an association is present, you'll need to test whether the associated object itself is present, and not the foreign key used to map the association. This way, it is not only checked that the foreign key is not empty but also that the referenced object exists.
class LineItem < ApplicationRecord
belongs_to :order
validates :order, presence: true
end
In order to validate associated records whose presence is required, you must
specify the :inverse_of option for the association:
NOTE: If you want to ensure that the association it is both present and valid, you also need to use validates_associated.
class Order < ApplicationRecord
has_many :line_items, inverse_of: :order
end
If you validate the presence of an object associated via a has_one or
has_many relationship, it will check that the object is neither blank? nor
marked_for_destruction?.
Since false.blank? is true, if you want to validate the presence of a boolean
field you should use one of the following validations:
validates :boolean_field_name, inclusion: [true, false]
validates :boolean_field_name, exclusion: [nil]
By using one of these validations, you will ensure the value will NOT be nil
which would result in a NULL value in most cases.
absence
This helper validates that the specified attributes are absent. It uses the
present? method to check if the value is not either nil or a blank string, that
is, a string that is either empty or consists of whitespace.
class Person < ApplicationRecord
validates :name, :login, :email, absence: true
end
If you want to be sure that an association is absent, you'll need to test whether the associated object itself is absent, and not the foreign key used to map the association.
class LineItem < ApplicationRecord
belongs_to :order
validates :order, absence: true
end
In order to validate associated records whose absence is required, you must
specify the :inverse_of option for the association:
class Order < ApplicationRecord
has_many :line_items, inverse_of: :order
end
If you validate the absence of an object associated via a has_one or
has_many relationship, it will check that the object is neither present? nor
marked_for_destruction?.
Since false.present? is false, if you want to validate the absence of a boolean
field you should use validates :field_name, exclusion: { in: [true, false] }.
The default error message is "must be blank".
uniqueness
This helper validates that the attribute's value is unique right before the object gets saved. It does not create a uniqueness constraint in the database, so it may happen that two different database connections create two records with the same value for a column that you intend to be unique. To avoid that, you must create a unique index on that column in your database.
class Account < ApplicationRecord
validates :email, uniqueness: true
end
The validation happens by performing an SQL query into the model's table, searching for an existing record with the same value in that attribute.
There is a :scope option that you can use to specify one or more attributes that
are used to limit the uniqueness check:
class Holiday < ApplicationRecord
validates :name, uniqueness: { scope: :year,
message: "should happen once per year" }
end
Should you wish to create a database constraint to prevent possible violations of a uniqueness validation using the :scope option, you must create a unique index on both columns in your database. See the MySQL manual for more details about multiple column indexes or the PostgreSQL manual for examples of unique constraints that refer to a group of columns.
There is also a :case_sensitive option that you can use to define whether the
uniqueness constraint will be case sensitive or not. This option defaults to
true.
class Person < ApplicationRecord
validates :name, uniqueness: { case_sensitive: false }
end
WARNING. Note that some databases are configured to perform case-insensitive searches anyway.
The default error message is "has already been taken".
validates_with
This helper passes the record to a separate class for validation.
class GoodnessValidator < ActiveModel::Validator
def validate(record)
if record.first_name == "Evil"
record.errors.add :base, "This person is evil"
end
end
end
class Person < ApplicationRecord
validates_with GoodnessValidator
end
NOTE: Errors added to record.errors[:base] relate to the state of the record
as a whole, and not to a specific attribute.
The validates_with helper takes a class, or a list of classes to use for
validation. There is no default error message for validates_with. You must
manually add errors to the record's errors collection in the validator class.
To implement the validate method, you must have a record parameter defined,
which is the record to be validated.
Like all other validations, validates_with takes the :if, :unless and
:on options. If you pass any other options, it will send those options to the
validator class as options:
class GoodnessValidator < ActiveModel::Validator
def validate(record)
if options[:fields].any? { |field| record.send(field) == "Evil" }
record.errors.add :base, "This person is evil"
end
end
end
class Person < ApplicationRecord
validates_with GoodnessValidator, fields: [:first_name, :last_name]
end
Note that the validator will be initialized only once for the whole application life cycle, and not on each validation run, so be careful about using instance variables inside it.
If your validator is complex enough that you want instance variables, you can easily use a plain old Ruby object instead:
class Person < ApplicationRecord
validate do |person|
GoodnessValidator.new(person).validate
end
end
class GoodnessValidator
def initialize(person)
@person = person
end
def validate
if some_complex_condition_involving_ivars_and_private_methods?
@person.errors.add :base, "This person is evil"
end
end
# ...
end
validates_each
This helper validates attributes against a block. It doesn't have a predefined
validation function. You should create one using a block, and every attribute
passed to validates_each will be tested against it. In the following example,
we don't want names and surnames to begin with lower case.
class Person < ApplicationRecord
validates_each :name, :surname do |record, attr, value|
record.errors.add(attr, 'must start with upper case') if value =~ /\A[[:lower:]]/
end
end
The block receives the record, the attribute's name, and the attribute's value. You can do anything you like to check for valid data within the block. If your validation fails, you should add an error to the model, therefore making it invalid.
Common Validation Options
These are common validation options:
:allow_nil
The :allow_nil option skips the validation when the value being validated is
nil.
class Coffee < ApplicationRecord
validates :size, inclusion: { in: %w(small medium large),
message: "%{value} is not a valid size" }, allow_nil: true
end
For full options to the message argument please see the message documentation.
:allow_blank
The :allow_blank option is similar to the :allow_nil option. This option
will let validation pass if the attribute's value is blank?, like nil or an
empty string for example.
class Topic < ApplicationRecord
validates :title, length: { is: 5 }, allow_blank: true
end
Topic.create(title: "").valid? # => true
Topic.create(title: nil).valid? # => true
:message
As you've already seen, the :message option lets you specify the message that
will be added to the errors collection when validation fails. When this
option is not used, Active Record will use the respective default error message
for each validation helper. The :message option accepts a String or Proc.
A String :message value can optionally contain any/all of %{value},
%{attribute}, and %{model} which will be dynamically replaced when
validation fails. This replacement is done using the I18n gem, and the
placeholders must match exactly, no spaces are allowed.
A Proc :message value is given two arguments: the object being validated, and
a hash with :model, :attribute, and :value key-value pairs.
class Person < ApplicationRecord
# Hard-coded message
validates :name, presence: { message: "must be given please" }
# Message with dynamic attribute value. %{value} will be replaced
# with the actual value of the attribute. %{attribute} and %{model}
# are also available.
validates :age, numericality: { message: "%{value} seems wrong" }
# Proc
validates :username,
uniqueness: {
# object = person object being validated
# data = { model: "Person", attribute: "Username", value: <username> }
message: ->(object, data) do
"Hey #{object.name}, #{data[:value]} is already taken."
end
}
end
:on
The :on option lets you specify when the validation should happen. The
default behavior for all the built-in validation helpers is to be run on save
(both when you're creating a new record and when you're updating it). If you
want to change it, you can use on: :create to run the validation only when a
new record is created or on: :update to run the validation only when a record
is updated.
class Person < ApplicationRecord
# it will be possible to update email with a duplicated value
validates :email, uniqueness: true, on: :create
# it will be possible to create the record with a non-numerical age
validates :age, numericality: true, on: :update
# the default (validates on both create and update)
validates :name, presence: true
end
You can also use on: to define custom contexts. Custom contexts need to be
triggered explicitly by passing the name of the context to valid?,
invalid?, or save.
class Person < ApplicationRecord
validates :email, uniqueness: true, on: :account_setup
validates :age, numericality: true, on: :account_setup
end
person = Person.new(age: 'thirty-three')
person.valid? # => true
person.valid?(:account_setup) # => false
person.errors.messages
# => {:email=>["has already been taken"], :age=>["is not a number"]}
person.valid?(:account_setup) executes both the validations without saving
the model. person.save(context: :account_setup) validates person in the
account_setup context before saving.
When triggered by an explicit context, validations are run for that context, as well as any validations without a context.
class Person < ApplicationRecord
validates :email, uniqueness: true, on: :account_setup
validates :age, numericality: true, on: :account_setup
validates :name, presence: true
end
person = Person.new
person.valid?(:account_setup) # => false
person.errors.messages
# => {:email=>["has already been taken"], :age=>["is not a number"], :name=>["can't be blank"]}
Strict Validations
You can also specify validations to be strict and raise
ActiveModel::StrictValidationFailed when the object is invalid.
class Person < ApplicationRecord
validates :name, presence: { strict: true }
end
Person.new.valid? # => ActiveModel::StrictValidationFailed: Name can't be blank
There is also the ability to pass a custom exception to the :strict option.
class Person < ApplicationRecord
validates :token, presence: true, uniqueness: true, strict: TokenGenerationException
end
Person.new.valid? # => TokenGenerationException: Token can't be blank
Conditional Validation
Sometimes it will make sense to validate an object only when a given predicate
is satisfied. You can do that by using the :if and :unless options, which
can take a symbol, a Proc or an Array. You may use the :if
option when you want to specify when the validation should happen. If you
want to specify when the validation should not happen, then you may use the
:unless option.
Using a Symbol with :if and :unless
You can associate the :if and :unless options with a symbol corresponding
to the name of a method that will get called right before validation happens.
This is the most commonly used option.
class Order < ApplicationRecord
validates :card_number, presence: true, if: :paid_with_card?
def paid_with_card?
payment_type == "card"
end
end
Using a Proc with :if and :unless
It is possible to associate :if and :unless with a Proc object
which will be called. Using a Proc object gives you the ability to write an
inline condition instead of a separate method. This option is best suited for
one-liners.
class Account < ApplicationRecord
validates :password, confirmation: true,
unless: Proc.new { |a| a.password.blank? }
end
As Lambdas are a type of Proc, they can also be used to write inline
conditions in a shorter way.
validates :password, confirmation: true, unless: -> { password.blank? }
Grouping Conditional validations
Sometimes it is useful to have multiple validations use one condition. It can
be easily achieved using with_options.
class User < ApplicationRecord
with_options if: :is_admin? do |admin|
admin.validates :password, length: { minimum: 10 }
admin.validates :email, presence: true
end
end
All validations inside of the with_options block will have automatically
passed the condition if: :is_admin?
Combining Validation Conditions
On the other hand, when multiple conditions define whether or not a validation
should happen, an Array can be used. Moreover, you can apply both :if and
:unless to the same validation.
class Computer < ApplicationRecord
validates :mouse, presence: true,
if: [Proc.new { |c| c.market.retail? }, :desktop?],
unless: Proc.new { |c| c.trackpad.present? }
end
The validation only runs when all the :if conditions and none of the
:unless conditions are evaluated to true.
Performing Custom Validations
When the built-in validation helpers are not enough for your needs, you can write your own validators or validation methods as you prefer.
Custom Validators
Custom validators are classes that inherit from ActiveModel::Validator. These
classes must implement the validate method which takes a record as an argument
and performs the validation on it. The custom validator is called using the
validates_with method.
class MyValidator < ActiveModel::Validator
def validate(record)
unless record.name.start_with? 'X'
record.errors.add :name, "Need a name starting with X please!"
end
end
end
class Person
include ActiveModel::Validations
validates_with MyValidator
end
The easiest way to add custom validators for validating individual attributes
is with the convenient ActiveModel::EachValidator. In this case, the custom
validator class must implement a validate_each method which takes three
arguments: record, attribute, and value. These correspond to the instance, the
attribute to be validated, and the value of the attribute in the passed
instance.
class EmailValidator < ActiveModel::EachValidator
def validate_each(record, attribute, value)
unless value =~ /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\z/i
record.errors.add attribute, (options[:message] || "is not an email")
end
end
end
class Person < ApplicationRecord
validates :email, presence: true, email: true
end
As shown in the example, you can also combine standard validations with your own custom validators.
Custom Methods
You can also create methods that verify the state of your models and add
errors to the errors collection when they are invalid. You must then
register these methods by using the validate
(API)
class method, passing in the symbols for the validation methods' names.
You can pass more than one symbol for each class method and the respective validations will be run in the same order as they were registered.
The valid? method will verify that the errors collection is empty,
so your custom validation methods should add errors to it when you
wish validation to fail:
class Invoice < ApplicationRecord
validate :expiration_date_cannot_be_in_the_past,
:discount_cannot_be_greater_than_total_value
def expiration_date_cannot_be_in_the_past
if expiration_date.present? && expiration_date < Date.today
errors.add(:expiration_date, "can't be in the past")
end
end
def discount_cannot_be_greater_than_total_value
if discount > total_value
errors.add(:discount, "can't be greater than total value")
end
end
end
By default, such validations will run every time you call valid?
or save the object. But it is also possible to control when to run these
custom validations by giving an :on option to the validate method,
with either: :create or :update.
class Invoice < ApplicationRecord
validate :active_customer, on: :create
def active_customer
errors.add(:customer_id, "is not active") unless customer.active?
end
end
Working with Validation Errors
The valid? and invalid? methods only provide a summary status on validity. However you can dig deeper into each individual error by using various methods from the errors collection.
The following is a list of the most commonly used methods. Please refer to the ActiveModel::Errors documentation for a list of all the available methods.
errors
The gateway through which you can drill down into various details of each error.
This returns an instance of the class ActiveModel::Errors containing all errors,
each error is represented by an ActiveModel::Error object.
class Person < ApplicationRecord
validates :name, presence: true, length: { minimum: 3 }
end
person = Person.new
person.valid? # => false
person.errors.full_messages
# => ["Name can't be blank", "Name is too short (minimum is 3 characters)"]
person = Person.new(name: "John Doe")
person.valid? # => true
person.errors.full_messages # => []
errors[]
errors[] is used when you want to check the error messages for a specific attribute. It returns an array of strings with all error messages for the given attribute, each string with one error message. If there are no errors related to the attribute, it returns an empty array.
class Person < ApplicationRecord
validates :name, presence: true, length: { minimum: 3 }
end
person = Person.new(name: "John Doe")
person.valid? # => true
person.errors[:name] # => []
person = Person.new(name: "JD")
person.valid? # => false
person.errors[:name] # => ["is too short (minimum is 3 characters)"]
person = Person.new
person.valid? # => false
person.errors[:name]
# => ["can't be blank", "is too short (minimum is 3 characters)"]
errors.where and error object
Sometimes we may need more information about each error beside its message. Each error is encapsulated as an ActiveModel::Error object, and where method is the most common way of access.
where returns an array of error objects, filtered by various degree of conditions.
class Person < ApplicationRecord
validates :name, presence: true, length: { minimum: 3 }
end
person = Person.new
person.valid? # => false
>> person.errors.where(:name) # errors linked to :name attribute
>> person.errors.where(:name, :too_short) # further filtered to only :too_short type error
You can read various information from these error objects:
>> error = person.errors.where(:name).last
>> error.attribute # => :name
>> error.type # => :too_short
>> error.options[:count] # => 3
You can also generate the error message:
error.message # => "is too short (minimum is 3 characters)" error.full_message # => "Name is too short (minimum is 3 characters)"
The full_message method generates a more user-friendly message, with the capitalized attribute name prepended.
errors.add
The add method creates the error object by taking the attribute, the error type and additional options hash. This is useful for writing your own validator.
class Person < ApplicationRecord
validate do |person|
errors.add :name, :too_plain, message: "is not cool enough"
end
end
person = Person.create
person.errors.where(:name).first.type # => :too_plain
person.errors.where(:name).first.full_message # => "Name is not cool enough"
errors[:base]
You can add errors that are related to the object's state as a whole, instead of being related to a specific attribute. You can add errors to :base when you want to say that the object is invalid, no matter the values of its attributes.
class Person < ApplicationRecord
validate do |person|
errors.add :base, :invalid, message: "This person is invalid because ..."
end
end
person = Person.create
person.errors.where(:base).first.full_message # => "This person is invalid because ..."
errors.clear
The clear method is used when you intentionally want to clear the errors collection. Of course, calling errors.clear upon an invalid object won't actually make it valid: the errors collection will now be empty, but the next time you call valid? or any method that tries to save this object to the database, the validations will run again. If any of the validations fail, the errors collection will be filled again.
class Person < ApplicationRecord
validates :name, presence: true, length: { minimum: 3 }
end
person = Person.new
person.valid? # => false
person.errors.empty? # => false
person.errors.clear
person.errors.empty? # => true
person.save # => false
person.errors.empty? # => false
errors.size
The size method returns the total number of errors for the object.
class Person < ApplicationRecord
validates :name, presence: true, length: { minimum: 3 }
end
person = Person.new
person.valid? # => false
person.errors.size # => 2
person = Person.new(name: "Andrea", email: "andrea@example.com")
person.valid? # => true
person.errors.size # => 0
Displaying Validation Errors in Views
Once you've created a model and added validations, if that model is created via a web form, you probably want to display an error message when one of the validations fail.
Because every application handles this kind of thing differently, Rails does
not include any view helpers to help you generate these messages directly.
However, due to the rich number of methods Rails gives you to interact with
validations in general, you can build your own. In addition, when
generating a scaffold, Rails will put some ERB into the _form.html.erb that
it generates that displays the full list of errors on that model.
Assuming we have a model that's been saved in an instance variable named
@article, it looks like this:
<% if @article.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(@article.errors.count, "error") %> prohibited this article from being saved:</h2>
<ul>
<% @article.errors.each do |error| %>
<li><%= error.full_message %></li>
<% end %>
</ul>
</div>
<% end %>
Furthermore, if you use the Rails form helpers to generate your forms, when
a validation error occurs on a field, it will generate an extra <div> around
the entry.
<div class="field_with_errors">
<input id="article_title" name="article[title]" size="30" type="text" value="">
</div>
You can then style this div however you'd like. The default scaffold that Rails generates, for example, adds this CSS rule:
.field_with_errors {
padding: 2px;
background-color: red;
display: table;
}
This means that any field with an error ends up with a 2 pixel red border.