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 < ActiveRecord::Base 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 makes them easy to use, 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, 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 with in 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 simple
Active Record class:
class Person < ActiveRecord::Base end
We can see how it works by looking at some rails console
output:
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:
-
create
-
create!
-
save
-
save!
-
update
-
update!
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
, create
just
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_counter
-
increment!
-
increment_counter
-
toggle!
-
touch
-
update_all
-
update_attribute
-
update_column
-
update_columns
-
update_counters
Note that save
also has the ability to skip validations if
passed validate: false
as argument. This technique should be
used with caution.
-
save(validate: false)
valid?
and invalid?
¶ ↑
To verify whether or not an object is valid, Rails uses the
valid?
method. You can also use this method 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 < ActiveRecord::Base 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.messages
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 not
run when using new
.
class Person < ActiveRecord::Base validates :name, presence: true end >>
invalid?
is simply 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
errors 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 < ActiveRecord::Base validates :name, presence: true end >>
We'll cover validation errors in greater depth in the Working with Validation Errors section. For now, let's turn to the built-in validation helpers that Rails provides by default.
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 message is added
to the object's errors
collection, and this message 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 reading some text, or any similar concept. 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 just create a virtual attribute).
class Person < ActiveRecord::Base validates :terms_of_service, acceptance: true end
The default error message for this helper is “must be accepted”.
It can receive an :accept
option, which determines the value
that will be considered acceptance. It defaults to “1” and can be easily
changed.
class Person < ActiveRecord::Base validates :terms_of_service, acceptance: { accept: 'yes' } end
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 < ActiveRecord::Base 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 < ActiveRecord::Base 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 this guide):
class Person < ActiveRecord::Base validates :email, confirmation: true validates :email_confirmation, presence: true 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 < ActiveRecord::Base 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.
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 < ActiveRecord::Base 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 < ActiveRecord::Base 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.
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 < ActiveRecord::Base 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 < ActiveRecord::Base validates :bio, length: { maximum: 1000, too_long: "%{count} characters is the maximum allowed" } end
This helper counts characters by default, but you can split the value in a
different way using the :tokenizer
option:
class Essay < ActiveRecord::Base validates :content, length: { minimum: 300, maximum: 400, tokenizer: lambda { |str| str.split(/\s+/) }, too_short: "must have at least %{count} words", too_long: "must have at most %{count} words" } 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.
If you 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
.
WARNING. Note that the regular expression above allows a trailing newline character.
class Player < ActiveRecord::Base validates :points, numericality: true validates :games_played, numericality: { only_integer: true } end
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 the supplied value. The default error message for this option is “must be less than or equal to %{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”.
The default error message 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 < ActiveRecord::Base 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.
class LineItem < ActiveRecord::Base 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:
class Order < ActiveRecord::Base 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, presence: true validates :boolean_field_name, inclusion: { in: [true, false] } validates :boolean_field_name, exclusion: { in: [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 < ActiveRecord::Base 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 < ActiveRecord::Base 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 < ActiveRecord::Base 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 both columns in your database. See the MySQL manual for more details about multiple column indexes.
class Account < ActiveRecord::Base 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 other
attributes that are used to limit the uniqueness check:
class Holiday < ActiveRecord::Base validates :name, uniqueness: { scope: :year, message: "should happen once per year" } end
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 < ActiveRecord::Base 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[:base] << "This person is evil" end end end class Person < ActiveRecord::Base 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[:base] << "This person is evil" end end end class Person < ActiveRecord::Base 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 < ActiveRecord::Base 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[: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 < ActiveRecord::Base 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 message 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 < ActiveRecord::Base validates :size, inclusion: { in: %w(small medium large), message: "%{value} is not a valid size" }, allow_nil: true end
: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 < ActiveRecord::Base 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.
: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 < ActiveRecord::Base # 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
Strict Validations¶ ↑
You can also specify validations to be strict and raise
ActiveModel::StrictValidationFailed
when the object is
invalid.
class Person < ActiveRecord::Base validates :name, presence: { strict: true } end Person.new.valid? # => ActiveModel::StrictValidationFailed: Name can't be blank
There is also an ability to pass custom exception to :strict
option.
class Person < ActiveRecord::Base 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 string, 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 < ActiveRecord::Base validates :card_number, presence: true, if: :paid_with_card? def paid_with_card? payment_type == "card" end end
Using a String with :if
and :unless
¶ ↑
You can also use a string that will be evaluated using eval
and needs to contain valid Ruby code. You should use this option only when
the string represents a really short condition.
class Person < ActiveRecord::Base validates :surname, presence: true, if: "name.nil?" end
Using a Proc with :if
and :unless
¶ ↑
Finally, it's 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 < ActiveRecord::Base validates :password, confirmation: true, unless: Proc.new { |a| a.password.blank? } end
Grouping Conditional validations¶ ↑
Sometimes it is useful to have multiple validations use one condition, it
can be easily achieved using with_options
.
class User < ActiveRecord::Base with_options if: :is_admin? do |admin| admin.validates :password, length: { minimum: 10 } admin.validates :email, presence: true end end
All validations inside of 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 < ActiveRecord::Base validates :mouse, presence: true, if: ["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 extend
ActiveModel::Validator
. These classes must implement a
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.starts_with? 'X' record.errors[: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[attribute] << (options[:message] || "is not an email") end end end class Person < ActiveRecord::Base 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
messages 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.
class Invoice < ActiveRecord::Base 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?
. 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 < ActiveRecord::Base validate :active_customer, on: :create def active_customer errors.add(:customer_id, "is not active") unless customer.active? end end
Working with Validation Errors¶ ↑
In addition to the valid?
and invalid?
methods
covered earlier, Rails provides a number of methods for working with the
errors
collection and inquiring about the validity of objects.
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
¶ ↑
Returns an instance of the class ActiveModel::Errors
containing all errors. Each key is the attribute name and the value is an
array of strings with all errors.
class Person < ActiveRecord::Base validates :name, presence: true, length: { minimum: 3 } end person = Person.new person.valid? # => false person.errors.messages # => {:name=>["can't be blank", "is too short (minimum is 3 characters)"]} person = Person.new(name: "John Doe") person.valid? # => true person.errors.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 < ActiveRecord::Base 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.add
¶ ↑
The add
method lets you manually add messages that are related
to particular attributes. You can use the errors.full_messages
or errors.to_a
methods to view the messages in the form they
might be displayed to a user. Those particular messages get the attribute
name prepended (and capitalized). add
receives the name of the
attribute you want to add the message to, and the message itself.
class Person < ActiveRecord::Base def a_method_used_for_validation_purposes errors.add(:name, "cannot contain the characters !@#%*()_-+=") end end person = Person.create(name: "!@#") person.errors[:name] # => ["cannot contain the characters !@#%*()_-+="] person.errors.full_messages # => ["Name cannot contain the characters !@#%*()_-+="]
Another way to do this is using []=
setter
class Person < ActiveRecord::Base def a_method_used_for_validation_purposes errors[:name] = "cannot contain the characters !@#%*()_-+=" end end person = Person.create(name: "!@#") person.errors[:name] # => ["cannot contain the characters !@#%*()_-+="] person.errors.to_a # => ["Name cannot contain the characters !@#%*()_-+="]
errors[:base]
¶ ↑
You can add error messages that are related to the object's state as a
whole, instead of being related to a specific attribute. You can use this
method when you want to say that the object is invalid, no matter the
values of its attributes. Since errors[:base]
is an array, you
can simply add a string to it and it will be used as an error message.
class Person < ActiveRecord::Base def a_method_used_for_validation_purposes errors[:base] << "This person is invalid because ..." end end
errors.clear
¶ ↑
The clear
method is used when you intentionally want to clear
all the messages in 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 < ActiveRecord::Base validates :name, presence: true, length: { minimum: 3 } end person = Person.new person.valid? # => false person.errors[:name] # => ["can't be blank", "is too short (minimum is 3 characters)"] person.errors.clear person.errors.empty? # => true p.save # => false p.errors[:name] # => ["can't be blank", "is too short (minimum is 3 characters)"]
errors.size
¶ ↑
The size
method returns the total number of error messages for
the object.
class Person < ActiveRecord::Base 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, it's fairly easy to 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
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.