@valueflows/vf-graphql

vf-graphql

GraphQL reference implementation of the ValueFlows grammar.

• API
  • Generating schemas
  • Accessing schemas
  • Validating implementations
• Implementing
  • Resolver logic
  • Scalar type resolvers
    • Dates & times
    • URIs
• Development setup
  • Prerequisites
  • Initialising for development
  • Available commands
• Contributing
  • Directory structure
  • Code structure
  • Publishing to NPM
• License

This project synchronizes projects implementing VF for a GraphQL interface between client and server. It includes:

• A GraphQL-native specification of the core VF grammar
• Complementary schemas not part of the RDF-based VF spec but needed for all VF implementations of economic software (for example Agent, Person, Organization, SpatialThing, note, image).
• Formal definition of mutation, query & subscriptions APIs
• Formal definition of available query parameters
• Inverse relationship naming
• Composable GraphQL schemas, TypeScript and FlowType definitions
• Runtime composition of schema modules into application-specific APIs which implement subsets of the ValueFlows vocabulary

API

The top-level module export contains three methods: buildSchema, printSchema and validate.

Generating schemas

The buildSchema method allows you to dynamically create schemas for the entire ValueFlows specification, or modular subsets of it. The full schema is broken down into modules of functionality, so that implementations which only aim to cover part of the specification can do so.

• When run without arguments, buildSchema will return a GraphQLSchema object for the entire ValueFlows API, including all optional and auxiliary modules.
• When passed an array, it builds a subset of the full spec which includes only the specified modules. For a complete list of modules, see schemaModules in schema-manifest.js or refer to the filenames in lib/schemas.
• An optional second argument allows for custom extensions to the core specification to be injected, where implementations include additional domain-specific logic that is not part of ValueFlows. Simply pass an array of GraphQL SDL schema strings and these will be merged into the resultant schema.

Accessing schemas

printSchema from the graphql module is also exported to make it easy to turn the built schema objects created by buildSchema into SDL strings, as some tooling requires this input format.

Therefore, if you need access to a string version of any schema you can get an SDL version with:

printSchema(buildSchema(/* [...] */))

If all you need is the entire schema as a string, consider importing @valueflows/vf-graphql/ALL_VF_SDL or @valueflows/vf-graphql/json-schema.json instead.

Validating implementations

validate has the same parameters as buildSchema, but takes another GraphQL schema as its first argument and validates it against a schema generated from the given set of module IDs and extension schemas. The output format is that of GraphQL's findBreakingChanges method.

Implementing

To implement a system gateway compatible with the ValueFlows spec, you will need to define the following:

Resolver logic

Resolver methods which bind to your application services must be implemented. In traditional client/server architecture, this is usually done serverside and the implementation executes remotely. In distributed/decentralised systems it is usually important that this be done in the client app to avoid adding any extra centralised services to your infrastructure.

If using Apollo GraphQL, this means defining an implementation object which contains methods for resolving all relationship fields. This object is passed to makeExecutableSchema along with the schema definition exported by this module.

Schemas will usually have to inject __typename parameters to disambiguate union types, especially for EventOrCommitment where there are no required fields which can determine the difference between the two records via duck-typing.

For a more detailed example, see the Holochain schema bindings.

Scalar type resolvers

Dates & times

Scalar type resolvers need to be provided for the ISO8601 DateTime type, in order to handle date encoding & decoding to your chosen storage system.

DateTime should be of variable precision, and allow specifying dates without time components as well as times without milliseconds. The timezone specifier may be omitted, but it is recommended to inject it manually prior to transmission to the server to ensure that specified times remain local to the user making the request.

URIs

There is also a separate URI type which simply makes it explicit when a reference to some external asset is expected. Implementations may treat these as strings, or perform URI validation as needed.

We usually suggest that you do not enforce an http/https protocol scheme, to allow for cross-system data linkage where records from distributed systems with their own URI resolution behaviour can be interlinked with web-based URLs.

Development setup

Prerequisites

• If you don't have Yarn- npm i -g yarn using the version of node you plan on developing this project against (for recommended, see .nvmrc). You can setup your modules manually using npm link if you prefer, but Yarn's workspaces feature will save you a lot of time.

Initialising for development

1. Run yarn from the top level folder of this repository to install and wire up all dependencies.
2. Run npm run build to compile the schema files.

Available commands

See scripts in package.json for the available commands. For quickly spinning up the full system, you should usually be able to simply run npm start. This will load up:

• Test runner for the schemas. It is recommended when authoring schemas to save often and watch the test output, as no line number information is available when debugging.
• A GraphiQL query UI at http://localhost:3000/graphql which you can use to test queries against a mock GraphQL API derived from the schema.
• A GraphQL Voyager UI at http://localhost:3000/viewer which shows an interactive visual representation useful for exploring the schema.

Contributing

The recommended way to contribute to this repo is via the npm run dev:schema command (also run as part of npm start). This will watch the code for changes and build & run tests every time you save a file. It's best to do it this way as the errors from the GraphQL parser can be hard to track down- more frequent feedback means you will catch any errors sooner.

Directory structure

The lib/ directory contains all source of the reference schema & validation helpers:

• index.js is the main entrypoint to the module, used by other packages wishing to validate schemas against the spec.
• tests/ contains tests for ensuring the schemas compile successfully.
• schemas/ contains the actual GraphQL schema definition files. These are the files you should edit.
  • schemas/bridging/ contains files which are automatically loaded in buildSchema. The filenames are dot-separated, and if all of the filename components are present in the module IDs passed then the schema is injected. For a list of available module IDs, see schema-manifest.js.
• build/, json-schema.json and the other *.js files are excluded from version control. They are generated from the schema definition files, using helper code in lib/scripts/.

Code structure

The "bridging" schema files in schemas/bridging/ create non-obvious behaviour within the top-level schema modules in schemas/. On first glance, some fields (eg. EconomicEvent.realizationOf) may appear to be missing from the record type definitions. However, this field's presence in the observation.agreement "bridging" schema means that it will automatically be added to the output schema if both observation and agreement are included. So— always check these files for a property before consider it missing as it may be part of a cross-module relationship or index.

The buildSchema helper defined in the module root manages all the logic for managing "bridging" schemas internally.

Publishing to NPM

• You will need to be given access to the VF NPM org in order to update the module on the registry. You can request access in https://gitter.im/valueflows/welcome
• Bump the version in lib/package.json & commit to the repository
• Update CHANGELOG.md with the new version ID and list of changes, and commit
• Run npm run publish from this directory
• Tag the current release in git and push the tag to origin

License

Released under an Apache 2.0 license.