Schemacop

This is the README for Schemacop version 2, which breaks backwards compatibility with version 1.

Schemacop validates ruby structures consisting of nested hashes and arrays against schema definitions described by a simple DSL.

Examples:

schema = Schema.new do
  req :naming, :hash do
    opt :first_name, :string
    req :last_name, :string
  end
  opt! :age, :integer, min: 18
  req? :password do
    type :string, check: proc { |pw| pw.include?('*') }
    type :integer
  end
end

schema.validate!(
  naming: { first_name: 'John',
            last_name: 'Doe' },
  age: 34,
  password: 'my*pass'
)

schema2 = Schema.new do
  req :description,
      :string,
      if: proc { |str| str.start_with?('Abstract: ') },
      max: 35,
      check: proc { |str| !str.end_with?('.') }
  req :description, :string, min: 35
end

schema2.validate!(description: 'Abstract: a short description')
schema2.validate!(description: 'Since this is no abstract, we expect it to be longer.')

Installation

To install the Schemacop gem:

$ gem install schemacop

To install it using bundler (recommended for any application), add it to your Gemfile:

gem 'schemacop'

Basics

Since there is no explicit typing in Ruby, it can be hard to make sure that a method is recieving exactly the right kind of data it needs. The idea of this gem is to define a schema at boot time that will validate the data being passed around at runtime. Those two steps look as follows:

At boot time:

my_schema = Schema.new do
  # Your specification goes here
end

At runtime:

my_schema.validate!(
  # Your data goes here
)

validate! will fail if the data given to it does not match what was specified in the schema.

Type lines vs. Field lines

Schemacop uses a DSL (domain-specific language) to let you describe your schemas. We distinguish between two kinds of identifiers:

Field Lines: We call a key-value pair (like the contents of a hash) a field. A field line typically starts with the keyword req (for a required field) or opt (for an optional field).
Type Lines: Those start with the keyword type and specify the data type to be accepted with a corresponding symbol (e.g. :integer or :boolean). You can have multiple Type Lines for a Field Line in order to indicate that the field's value can be of one of the specified types.

If you don't use any short forms, a schema definition would be something like this:

s = Schema.new do
  type :integer
  type :hash do
    req 'name' do
      type :boolean
    end
  end
end

The above schema would accept either an integer or a hash with exactly one field with key 'present' of type String and value of type Boolean (either TrueClass or FalseClass).

We will see Type and Field lines in more detail below.

`validate` vs `validate!` vs `valid?`

The method validate will return a Collector object that contains all validation errors (if any), whereas validate! will accumulate all violations and finally throw an exception describing them.

For simply querying the validity of some data, use the methods valid? or invalid?.

Schemacop's DSL

In this section, we will ignore short forms and explicitly write out everything.

Inside the block given at the schema instantiation (Schema.new do ... end), the following kinds of method calls are allowed (where the outermost must be a Type Line):

Type Line

A Type Line always starts with the identifier type and specifies a possible data type for a given field (if inside a Field Line) or the given data structure (if directly below the schema instantiation).

Type Lines are generally of the form

type :my_type, option_1: value_1, ..., option_n: value_n

where :my_type is a supported symbol (see section Types below for supported types).

General options

Some types support specific options that allow additional checks on the nature of the data (such as the min option for type :number). The following options are supported by all types:

Option `if`

This option takes a proc (or a lambda) as value. The proc will be called when checking whether or not the data being analyzed fits a certain type. The data is given to the proc, which has to return either true or false. If it returns true, the type of the given data is considered correct and the data will be validated if further options are given.

Note that the proc in if will only get called if the type (:my_type from above) fits the data already. You can use the option if in order to say: "Even if the data is of type :my_type, I consider it having the wrong type if my proc returns false."

Consider a scenario in which you want to have the following rule set:

Only integers may be given
Odd integers must be no larger than 15
No limitations for even integers

The corresponding schema would look as follows:

Schma.new do
  type :integer, if: proc { |data| data.odd? }, max: 15
  type :integer
end

Here, the first type line will only accept odd numbers and the option max: 15 provided by the :integer validator will discard numbers higher than 15.

Since the first line only accepts odd numbers, it doesn't apply for even numbers (due to the proc given to if they are considered to be of the wrong type) and control falls through to the second type line accepting any integer.

Option `check`

This option allows you to perform arbitrary custom checks for a given data type. Just like if, check takes a proc or lambda as a value, but it runs after the type checking, meaning that it only gets executed if the data has the right type and the proc in if (if any) has returned true.

The proc passed to the check option is given the data being analyzed. It is to return true if the data passes the custom check. If it returns false, Schemacop considers the data to be invalid.

The following example illustrates the use of the option check: Consider a scenario in which you want the following rule set:

Data must be of type String
The string must be longer than 5 characters
The second character must be an 'r'

The corresponding schema would look as follows:

Schema.new do
  type :string, min: 5, check: proc { |data| data[1] == 'r'}
end

The above Type Line has type :string and two options (min and check). The option min is supported by the :string validator (covered later).

Field Line

Inside a Type Line of type :hash, you may specify an arbitrary number of field lines (one for each key-value pair you want to be in the hash).

Field Lines start with one of the following six identifiers: req, req?, req!, opt, opt? or opt!:

The suffix -! means that the field must not be nil.
The suffix -? means that the field may be nil.
The prefix req- denotes a required field (validation fails if the given data hash doesn't define it). req is a shorthand notation for req! (meaning that by default, a required field cannot be nil).
The prefix opt- denotes an optional field. opt is a shorthand notation for opt? (meaning that by default, an optional field may be nil).

To summarize:

req or req!: required and non-nil
req?: required but may be nil
opt or opt?: optional and may be nil
opt!: optional but non-nil

You then pass a block with a single or multiple Type Lines to the field.

Example: The following schema defines a hash that has a required non-nil field of type String under the key :name (of type Symbol) and an optional but non-nil field of type Integer or Date under the key :age.

Schema.new do
  type :hash do
    req :name do
      type :string
    end
    opt! :age do
      type :integer
      type :object, classes: Date
    end
  end
end

You might find the notation cumbersome, and you'd be right to say so. Luckily there are plenty of short forms available which we will see below.

Handling hashes with indifferent access

Schemacop has special handling for objects of the class ActiveSupport::HashWithIndifferentAccess: You may specify the keys as symbols or strings, and Schemacop will handle the conversion necessary for proper validation internally. Note that if you define the same key as string and symbol, it will throw a ValidationError exception when asked to validate a hash with indifferent access.

Thus, the following two schema definitions are equivalent when validating a hash with indifferent access:

Schema.new do
  type :hash do
    req :name do
      type :string
    end
  end
end

Schema.new do
  type :hash do
    req 'name' do
      type :string
    end
  end
end

Types

Types are defined via their validators, which is a class under validator/. Each validator is sourced by schemacop.rb.

The following types are supported by Schemacop by default:

:boolean accepts a Ruby TrueClass or FalseClass instance.
:integer accepts a Ruby Integer.
- supported options: min, max (lower / upper bound)
:float accepts a Ruby Float.
- supported options: min, max (lower / upper bound)
:number accepts a Ruby Integer or Float.
- supported options: min, max (lower / upper bound)
:string accepts a Ruby String.
- supported options: min, max (bounds for string length)
:symbol accepts a Ruby Symbol.
:object accepts an arbitrary Ruby object (any object if no option is given).

Supported options:

classes: Ruby class (or an array of them) that will be the only recognized filters. Unlike other options, this one affects not the validation but the type recognition, meaning that you can have multiple Type Lines with different classes option for the same field, each having its own validation (e.g. through the option check).
strict: Boolean option, defaults to true. If set to false, the validator also allows derived classes of those specified with classes.
- :array accepts a Ruby Array.
supported options: min, max (bounds for array size) and nil: TODO
accepts a block with an arbitrary number of Type Lines.
TODO no lookahead for different arrays, see validator_array_test#test_multiple_arrays
- :hash accepts a Ruby Hash or an ActiveSupport::HashWithIndifferentAccess.
accepts a block with an arbitrary number of Field Lines.
- :nil: accepts a Ruby NilClass instance. If you want to allow nil as a value in a field, see above for the usage of the suffixes -! and -? for Field Lines.

All types support the options if and check (see the section about Type Lines above).

Short forms

For convenience, the following short forms may be used (and combined if possible).

Passing a type to a Field Line or schema

Instead of adding a Type Line in the block of a Field Line, you can omit do type ... end and directly write the type after the key of the field.

Note that when using this short form, you may not give a block to the Field Line.

# Long form
req :name do
  type :string, min: 2, max: 5
end

# Short form
req :name, :string, min: 2, max: 5

This means that the value under the key :name of type Symbol must be a String containing 2 to 5 characters.

The short form also works in the schema instantiation:

# Long form
Schema.new do
  type :string, min: 2, max: 5
end

# Short form
Schema.new(:string, min: 2, max: 5)

This means that the data given to the schema must be a String that is between 2 and 5 characters long.

Passing multiple types at once

You can specify several types at once by putting them in an array.

Note that when using this short form, you may not give any options.

# Long form
opt! :age do
  type :string
  type :integer
  type :boolean
end

# Short form
opt! :age do
  type [:string, :integer, :boolean]
end

Combined with previous short form:

opt! :age, [:string, :integer, :boolean]

This also works in the schema instantiation:

Schema.new([:string, :integer, :boolean])

This means that the schema will validate any data of type String, Integer, TrueClass or FalseClass.

Omitting the Type Line in a Field Line

If you don't specify the type of a field, it will default to :object with no options, meaning that the field will accept any kind of data:

# Long form
req? :child do
  type :object
end

# Short form
req? :child

Omitting the Type Line in schema instantiation

If you don't give a Type Line to a schema, it will accept data of type Hash. Therefore, if you validate Hashes only, you can omit the Type Line and directly write Field Lines in the schema instantiation:

# Long form
Schema.new do
  type :hash do
    req :name do
      # ...
    end
  end
end

# Short form
Schema.new do
  req :name do
    # ...
  end
end

Shortform for subtypes

In case of nested arrays, you can group all Type Lines to a single one.

Note that any options or block passed to the grouped Type Line will be given to the innermost (last) type.

# Long form
type :array do
  type :integer, min: 3
end

# Short form
type :array, :integer, min: 3

A more complex example:

Long form:

Schema.new do
  type :hash do
    req 'nutrition' do
      type :array do
        type :array do
          type :hash, check: proc { |h| h.member?(:food) || h.member?(:drink) } do
            opt! :food do
              type :object
            end
            opt! :drink do
              type :object
            end
          end
        end
      end
    end
  end
end

Short form (with this short form others from above):

Schema.new do
  req 'nutrition', :array, :array, :hash, check: proc { |h| h.member?(:food) || h.member?(:drink) } do
    opt! :food
    opt! :drink
  end
end

This example accepts a hash with exactly one String key 'nutrition' with value of type Array with children of type Array with children of type Hash in which at least one of the Symbol keys :food and :drink (with any non-nil value type) is present.

Exceptions

Schemacop will throw one of the following checked exceptions:

Schemacop::Exceptions::InvalidSchemaError

This exception is thrown when the given schema definition format is invalid.

Schemacop::Exceptions::ValidationError

This exception is thrown when the given data does not comply with the given schema definition.

Known limitations

Schemacop does not yet allow cyclic structures with infinite depth.
Schemacop aborts when it encounters an error. It is not able to collect a full list of multiple errors.
Schemacop is not made for validating complex causalities (i.e. field a needs to be given only if field b is present).
Schemacop does not yet support string regex matching.

Contributors

Thanks to Rubocop for great inspiration concerning their name and the structure of their README file. And special thanks to SubGit for their great open source licensing.