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GraPHPinator Constraint directives

:zap::globe_with_meridians::zap: Typesystem directives declare additional validation on the top of the GraphQL type system.

Introduction

This package allows server to declare additional constraints on accepted values for arguments, fields and input fields. It is also possible for client to declare constraints for variables in request document.

Additional benefit of using constraint directives is that expected values are displayed to client using GraphQL type language in a self-documenting manner.

Installation

Install package using composer

How to use

In order to enable constraint directives on your server, the only thing you need to do is to put selected directives to your Container. To avoid cyclic dependencies ConstraintDirectiveAccessor must be implemented. This step should be automated when using a DI solution.

Here is example configuration for Nette DI:

Add constraint to Argument

The most common usage of constraint directives is to validate input from client without having to do it yourself in the resolve function.

Add constraint to Field

Additional usage of constraint directives is to validate output from your resolve functions.

Add constraint to Type & Interface & InputType

Special case is ObjectConstraint which declares additional information on which fields must be filled. It is a flexible solution to the input-union problem, but can also be applied on Interface/Type to semantically indicate which values are returned.

Variance

Question of variance comes into play because field, argument, and object constraints can be declared in an interface context and then implemented by the concrete type. Traditional rules apply here.

• Covariance for Field constraints - child can restrict parent's constraint, but may not release it.
• Contravariance for Argument constraints - child can soften parent's constraint, but may not restrict it.
• Invariance for Object constraints - child must contain the same constraint as parent.

Directive options

• @stringConstraint
  • minLength - Int
  • maxLength - Int
  • regex - String
  • oneOf - [String!]
• @intConstraint
  • min - Int
  • max - Int
  • oneOf - [Int!]
• @floatConstraint
  • min - Float
  • max - Float
  • oneOf - [Float!]
• @listConstraint
  • minItems - Int
  • maxItems - Int
  • unique - Boolean
  • innerList - object with the same arguments to recursivelly apply constraint to inner list
• @uploadConstraint
  • maxSize - Int
  • mimeType - [String!]
• @objectConstraint
  • atLeastOne - [String!]
  • atMostOne - [String!]
  • exactlyOne - [String!]
  • atLeast - {count: Int!, from: [String!]!}
  • atMost - {count: Int!, from: [String!]!}
  • exactly - {count: Int!, from: [String!]!}