benmccallum/fairybread

Input validation for Hot Chocolate.

Getting started

Install a compatible version.

dotnet add package FairyBread

Configure services.

// Add your FluentValidation validators
// (note: this will add all validators in the assembly that contains `CreateUserInputValidator`)
services.AddValidatorsFromAssemblyContaining<CreateUserInputValidator>();

// Add FairyBread
services
    .AddGraphQL()
    .AddFairyBread();

Configure FluentValidation validators on your input types.

public class CreateUserInput { ... }

public class CreateUserInputValidator : AbstractValidator<CreateUserInput> { ... }

// An example GraphQL field in Hot Chocolate
public Task CreateUser(CreateUserInput userInput) { ... }

How validation errors will be handled

By default, errors will be written out into the GraphQL execution result in the Errors property with one error being reported per failure on a field. You can change this behaviour by implementing your own IValidationErrorsHandler.

Implicit vs explicit configuration

FairyBread opts for an implicit approach to validation by default, similar to how FluentValidation.AspNetCore behaves. Simply create a validator for a certain input object type and arguments of that type will be validated. And you don't need to worry about a middleware performance penalty, as FairyBread (since v7.1) only adds the validation field middleware where needed.

There are some cases though where explicitness is either required or useful, so you can do that too.

For example, if you've got a field argument that's a scalar type (e.g. not an input type), like an int, creating a validator targeting int would mean every top-level int argument across your schema would be implicitly validated, which wouldn't make sense. Instead, annotate the validator by having it inherit IExplicitUsageOnlyValidator and then explicitly setup it up on the argument (see below).

Annotation API:

• [Validate(typeof(FooValidator)] - explicitly add this validator for the argument
• [DontValidate] - don't validate this argument at all
• [DontImplicitlyValidate] - disable implicit validators for the argument

Fluent API:

• .Argument("foo").ValidateWith<FooValidator>()
• .DontValidate()
• .DontImplicitlyValidate()

Dealing with multi-threaded execution issues

GraphQL resolvers are inherently multi-threaded; as such, you can run into issues injecting things like an EntityFramework DbContext into a field resolver (or something it uses) which doesn't allow muli-thread usage. One solution for this is to resolve DbContext into its own "scope", rather than the default scope (for an ASP.NET Core application this is the HTTP Request).

With FairyBread, you might need to do this if one of your validators uses a DbContext and could operate on the scoped DbContext at the same time as another part of the application. GraphQL mutation resolvers are executed serially, so typically you wouldn't encounter this issue for mutations. It's more likely you could encounter it for Query resolvers which can run in parallel.

Good news is, it's as easy as marking your validator with IRequiresOwnScopeValidator and we'll take care of the rest.

public class SomeInputValidator
    : AbstractValidator<SomeInput>
    , IRequiresOwnScopeValidator
{
    // db will be a unique instance for this validation operation
    public SomeInputValidator(SomeDbContext db) { ... } 
}

Using MediatR?

If you want to let MediatR fire validation, you can set up:

• FairyBread to skip validating MediatR.IRequest arguments,
• your MediatR pipeline to validate them and throw a ValidationException, and
• an IErrorFilter(in Hot Chocolate) to handle it using FairyBread.DefaultValidationErrorsHandler to report the errors.

Where to next?

For more examples, please see the tests.

Customization

FairyBread was built with customization in mind.

You can tweak the default settings as needed:

services.AddFairyBread(options =>
{
    options.ShouldValidateArgument = (objTypeDef, fieldTypeDef, argTypeDef) => ...;
    options.ThrowIfNoValidatorsFound = true/false;
});

You can completely swap in your own concrete implementations of bits with DI. These could be based on the default implementations whose methods can be overridden.

See CustomizationTests.cs.

Backlog

See issues.

Compatibility

FairyBread depends on HotChocolate.Execution which can bring breaking changes from time to time and require a major bump our end. This is also the case for FluentValidation. Compatibility is listed below.

Note, these are minimum versions, for instance, v12.0.1 through to 12.3.x of Hot Chocolate are supported by FairyBread v8.x.x.

We strive to match Hot Chocolate's supported .NET target frameworks, though this might not always be possible.

* Denotes unexpected binary incompatibility / breaking change in Hot Chocolate

What the heck is a fairy bread?

A (bizarre) Australian food served at children's parties. Since I'm Australian and HotChocolate has a lot of project names with sweet tendencies, this seemed like a fun name for the project.

According to wikipedia:

"Fairy bread is sliced white bread spread with butter or margarine and covered with sprinkles or "hundreds and thousands", served at children's parties in Australia and New Zealand. It is typically cut into triangles."