# GraphQL API This document outlines the styleguide for GitLab's [GraphQL API](../api/graphql/index.md). ## How GitLab implements GraphQL We use the [graphql-ruby gem](https://graphql-ruby.org/) written by [Robert Mosolgo](https://github.com/rmosolgo/). All GraphQL queries are directed to a single endpoint ([`app/controllers/graphql_controller.rb#execute`](https://gitlab.com/gitlab-org/gitlab/blob/master/app%2Fcontrollers%2Fgraphql_controller.rb)), which is exposed as an API endpoint at `/api/graphql`. ## Deep Dive In March 2019, Nick Thomas hosted a [Deep Dive](https://gitlab.com/gitlab-org/create-stage/issues/1) on GitLab's [GraphQL API](../api/graphql/index.md) to share his domain specific knowledge with anyone who may work in this part of the code base in the future. You can find the [recording on YouTube](https://www.youtube.com/watch?v=-9L_1MWrjkg), and the slides on [Google Slides](https://docs.google.com/presentation/d/1qOTxpkTdHIp1CRjuTvO-aXg0_rUtzE3ETfLUdnBB5uQ/edit) and in [PDF](https://gitlab.com/gitlab-org/create-stage/uploads/8e78ea7f326b2ef649e7d7d569c26d56/GraphQL_Deep_Dive__Create_.pdf). Everything covered in this deep dive was accurate as of GitLab 11.9, and while specific details may have changed since then, it should still serve as a good introduction. ## GraphiQL GraphiQL is an interactive GraphQL API explorer where you can play around with existing queries. You can access it in any GitLab environment on `https:///-/graphql-explorer`. For example, the one for [GitLab.com](https://gitlab.com/-/graphql-explorer). ## Authentication Authentication happens through the `GraphqlController`, right now this uses the same authentication as the Rails application. So the session can be shared. It is also possible to add a `private_token` to the querystring, or add a `HTTP_PRIVATE_TOKEN` header. ## Types We use a code-first schema, and we declare what type everything is in Ruby. For example, `app/graphql/types/issue_type.rb`: ```ruby graphql_name 'Issue' field :iid, GraphQL::ID_TYPE, null: true field :title, GraphQL::STRING_TYPE, null: true # we also have a method here that we've defined, that extends `field` markdown_field :title_html, null: true field :description, GraphQL::STRING_TYPE, null: true markdown_field :description_html, null: true ``` We give each type a name (in this case `Issue`). The `iid`, `title` and `description` are _scalar_ GraphQL types. `iid` is a `GraphQL::ID_TYPE`, a special string type that signifies a unique ID. `title` and `description` are regular `GraphQL::STRING_TYPE` types. When exposing a model through the GraphQL API, we do so by creating a new type in `app/graphql/types`. You can also declare custom GraphQL data types for scalar data types (e.g. `TimeType`). When exposing properties in a type, make sure to keep the logic inside the definition as minimal as possible. Instead, consider moving any logic into a presenter: ```ruby class Types::MergeRequestType < BaseObject present_using MergeRequestPresenter name 'MergeRequest' end ``` An existing presenter could be used, but it is also possible to create a new presenter specifically for GraphQL. The presenter is initialized using the object resolved by a field, and the context. ### Nullable fields GraphQL allows fields to be be "nullable" or "non-nullable". The former means that `null` may be returned instead of a value of the specified type. **In general**, you should prefer using nullable fields to non-nullable ones, for the following reasons: - It's common for data to switch from required to not-required, and back again - Even when there is no prospect of a field becoming optional, it may not be **available** at query time - For instance, the `content` of a blob may need to be looked up from Gitaly - If the `content` is nullable, we can return a **partial** response, instead of failing the whole query - Changing from a non-nullable field to a nullable field is difficult with a versionless schema Non-nullable fields should only be used when a field is required, very unlikely to become optional in the future, and very easy to calculate. An example would be `id` fields. Further reading: - [GraphQL Best Practices Guide](https://graphql.org/learn/best-practices/#nullability) - [Using nullability in GraphQL](https://blog.apollographql.com/using-nullability-in-graphql-2254f84c4ed7) ### Exposing Global IDs When exposing an `ID` field on a type, we will by default try to expose a global ID by calling `to_global_id` on the resource being rendered. To override this behaviour, you can implement an `id` method on the type for which you are exposing an ID. Please make sure that when exposing a `GraphQL::ID_TYPE` using a custom method that it is globally unique. The records that are exposing a `full_path` as an `ID_TYPE` are one of these exceptions. Since the full path is a unique identifier for a `Project` or `Namespace`. ### Connection Types GraphQL uses [cursor based pagination](https://graphql.org/learn/pagination/#pagination-and-edges) to expose collections of items. This provides the clients with a lot of flexibility while also allowing the backend to use different pagination models. To expose a collection of resources we can use a connection type. This wraps the array with default pagination fields. For example a query for project-pipelines could look like this: ```graphql query($project_path: ID!) { project(fullPath: $project_path) { pipelines(first: 2) { pageInfo { hasNextPage hasPreviousPage } edges { cursor node { id status } } } } } ``` This would return the first 2 pipelines of a project and related pagination info., ordered by descending ID. The returned data would look like this: ```json { "data": { "project": { "pipelines": { "pageInfo": { "hasNextPage": true, "hasPreviousPage": false }, "edges": [ { "cursor": "Nzc=", "node": { "id": "gid://gitlab/Pipeline/77", "status": "FAILED" } }, { "cursor": "Njc=", "node": { "id": "gid://gitlab/Pipeline/67", "status": "FAILED" } } ] } } } } ``` To get the next page, the cursor of the last known element could be passed: ```graphql query($project_path: ID!) { project(fullPath: $project_path) { pipelines(first: 2, after: "Njc=") { pageInfo { hasNextPage hasPreviousPage } edges { cursor node { id status } } } } } ``` To ensure that we get consistent ordering, we will append an ordering on the primary key, in descending order. This is usually `id`, so basically we will add `order(id: :desc)` to the end of the relation. A primary key _must_ be available on the underlying table. ### Exposing permissions for a type To expose permissions the current user has on a resource, you can call the `expose_permissions` passing in a separate type representing the permissions for the resource. For example: ```ruby module Types class MergeRequestType < BaseObject expose_permissions Types::MergeRequestPermissionsType end end ``` The permission type inherits from `BasePermissionType` which includes some helper methods, that allow exposing permissions as non-nullable booleans: ```ruby class MergeRequestPermissionsType < BasePermissionType present_using MergeRequestPresenter graphql_name 'MergeRequestPermissions' abilities :admin_merge_request, :update_merge_request, :create_note ability_field :resolve_note, description: 'Indicates the user can resolve discussions on the merge request' permission_field :push_to_source_branch, method: :can_push_to_source_branch? end ``` - **`permission_field`**: Will act the same as `graphql-ruby`'s `field` method but setting a default description and type and making them non-nullable. These options can still be overridden by adding them as arguments. - **`ability_field`**: Expose an ability defined in our policies. This behaves the same way as `permission_field` and the same arguments can be overridden. - **`abilities`**: Allows exposing several abilities defined in our policies at once. The fields for these will all have be non-nullable booleans with a default description. ## Feature flags Developers can add [feature flags](../development/feature_flags/index.md) to GraphQL fields in the following ways: - Add the `feature_flag` property to a field. This will allow the field to be _hidden_ from the GraphQL schema when the flag is disabled. - Toggle the return value when resolving the field. You can refer to these guidelines to decide which approach to use: - If your field is experimental, and its name or type is subject to change, use the `feature_flag` property. - If your field is stable and its definition will not change, even after the flag is removed, toggle the return value of the field instead. Note that [all fields should be nullable](#nullable-fields) anyway. ### `feature_flag` property The `feature_flag` property allows you to toggle the field's [visibility](https://graphql-ruby.org/authorization/visibility.html) within the GraphQL schema. This will remove the field from the schema when the flag is disabled. A description is [appended](https://gitlab.com/gitlab-org/gitlab/-/blob/497b556/app/graphql/types/base_field.rb#L44-53) to the field indicating that it is behind a feature flag. CAUTION: **Caution:** If a client queries for the field when the feature flag is disabled, the query will fail. Consider this when toggling the visibility of the feature on or off on production. The `feature_flag` property does not allow the use of [feature gates based on actors](../development/feature_flags/development.md). This means that the feature flag cannot be toggled only for particular projects, groups, or users, but instead can only be toggled globally for everyone. Example: ```ruby field :test_field, type: GraphQL::STRING_TYPE, null: true, description: 'Some test field', feature_flag: :my_feature_flag ``` ### Toggle the value of a field This method of using feature flags for fields is to toggle the return value of the field. This can be done in the resolver, in the type, or even in a model method, depending on your preference and situation. When applying a feature flag to toggle the value of a field, the `description` of the field must: - State that the value of the field can be toggled by a feature flag. - Name the feature flag. - State what the field will return when the feature flag is disabled (or enabled, if more appropriate). Example: ```ruby field :foo, GraphQL::STRING_TYPE, null: true, description: 'Some test field. Will always return `null`' \ 'if `my_feature_flag` feature flag is disabled' def foo object.foo unless Feature.enabled?(:my_feature_flag, object) end ``` ## Deprecating fields GitLab's GraphQL API is versionless, which means we maintain backwards compatibility with older versions of the API with every change. Rather than removing a field, we need to _deprecate_ the field instead. In future, GitLab [may remove deprecated fields](https://gitlab.com/gitlab-org/gitlab/issues/32292). Fields are deprecated using the `deprecated` property. The value of the property is a `Hash` of: - `reason` - Reason for the deprecation. - `milestone` - Milestone that the field was deprecated. Example: ```ruby field :token, GraphQL::STRING_TYPE, null: true, deprecated: { reason: 'Login via token has been removed', milestone: '10.0' }, description: 'Token for login' ``` The original `description:` of the field should be maintained, and should _not_ be updated to mention the deprecation. ### Deprecation reason styleguide Where the reason for deprecation is due to the field being replaced with another field, the `reason` must be: ```plaintext Use `otherFieldName` ``` Example: ```ruby field :designs, ::Types::DesignManagement::DesignCollectionType, null: true, deprecated: { reason: 'Use `designCollection`', milestone: '10.0' }, description: 'The designs associated with this issue', ``` If the field is not being replaced by another field, a descriptive deprecation `reason` should be given. ## Enums GitLab GraphQL enums are defined in `app/graphql/types`. When defining new enums, the following rules apply: - Values must be uppercase. - Class names must end with the string `Enum`. - The `graphql_name` must not contain the string `Enum`. For example: ```ruby module Types class TrafficLightStateEnum < BaseEnum graphql_name 'TrafficLightState' description 'State of a traffic light' value 'RED', description: 'Drivers must stop' value 'YELLOW', description: 'Drivers must stop when it is safe to' value 'GREEN', description: 'Drivers can start or keep driving' end end ``` If the enum will be used for a class property in Ruby that is not an uppercase string, you can provide a `value:` option that will adapt the uppercase value. In the following example: - GraphQL inputs of `OPENED` will be converted to `'opened'`. - Ruby values of `'opened'` will be converted to `"OPENED"` in GraphQL responses. ```ruby module Types class EpicStateEnum < BaseEnum graphql_name 'EpicState' description 'State of a GitLab epic' value 'OPENED', value: 'opened', description: 'An open Epic' value 'CLOSED', value: 'closed', description: 'An closed Epic' end end ``` ## Descriptions All fields and arguments [must have descriptions](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/16438). A description of a field or argument is given using the `description:` keyword. For example: ```ruby field :id, GraphQL::ID_TYPE, description: 'ID of the resource' ``` Descriptions of fields and arguments are viewable to users through: - The [GraphiQL explorer](#graphiql). - The [static GraphQL API reference](../api/graphql/#reference). ### Description styleguide To ensure consistency, the following should be followed whenever adding or updating descriptions: - Mention the name of the resource in the description. Example: `'Labels of the issue'` (issue being the resource). - Use `"{x} of the {y}"` where possible. Example: `'Title of the issue'`. Do not start descriptions with `The`. - Descriptions of `GraphQL::BOOLEAN_TYPE` fields should answer the question: "What does this field do?". Example: `'Indicates project has a Git repository'`. - Always include the word `"timestamp"` when describing an argument or field of type `Types::TimeType`. This lets the reader know that the format of the property will be `Time`, rather than just `Date`. - No `.` at end of strings. Example: ```ruby field :id, GraphQL::ID_TYPE, description: 'ID of the Issue' field :confidential, GraphQL::BOOLEAN_TYPE, description: 'Indicates the issue is confidential' field :closed_at, Types::TimeType, description: 'Timestamp of when the issue was closed' ``` ## Authorization Authorizations can be applied to both types and fields using the same abilities as in the Rails app. If the: - Currently authenticated user fails the authorization, the authorized resource will be returned as `null`. - Resource is part of a collection, the collection will be filtered to exclude the objects that the user's authorization checks failed against. Also see [authorizing resources in a mutation](#authorizing-resources). TIP: **Tip:** Try to load only what the currently authenticated user is allowed to view with our existing finders first, without relying on authorization to filter the records. This minimizes database queries and unnecessary authorization checks of the loaded records. ### Type authorization Authorize a type by passing an ability to the `authorize` method. All fields with the same type will be authorized by checking that the currently authenticated user has the required ability. For example, the following authorization ensures that the currently authenticated user can only see projects that they have the `read_project` ability for (so long as the project is returned in a field that uses `Types::ProjectType`): ```ruby module Types class ProjectType < BaseObject authorize :read_project end end ``` You can also authorize against multiple abilities, in which case all of the ability checks must pass. For example, the following authorization ensures that the currently authenticated user must have `read_project` and `another_ability` abilities to see a project: ```ruby module Types class ProjectType < BaseObject authorize [:read_project, :another_ability] end end ``` ### Field authorization Fields can be authorized with the `authorize` option. For example, the following authorization ensures that the currently authenticated user must have the `owner_access` ability to see the project: ```ruby module Types class MyType < BaseObject field :project, Types::ProjectType, null: true, resolver: Resolvers::ProjectResolver, authorize: :owner_access end end ``` Fields can also be authorized against multiple abilities, in which case all of ability checks must pass. **Note:** This requires explicitly passing a block to `field`: ```ruby module Types class MyType < BaseObject field :project, Types::ProjectType, null: true, resolver: Resolvers::ProjectResolver do authorize [:owner_access, :another_ability] end end end ``` NOTE: **Note:** If the field's type already [has a particular authorization](#type-authorization) then there is no need to add that same authorization to the field. ### Type and Field authorizations together Authorizations are cumulative, so where authorizations are defined on a field, and also on the field's type, then the currently authenticated user would need to pass all ability checks. In the following simplified example the currently authenticated user would need both `first_permission` and `second_permission` abilities in order to see the author of the issue. ```ruby class UserType authorize :first_permission end ``` ```ruby class IssueType field :author, UserType, authorize: :second_permission end ``` ## Resolvers We define how the application serves the response using _resolvers_ stored in the `app/graphql/resolvers` directory. The resolver provides the actual implementation logic for retrieving the objects in question. To find objects to display in a field, we can add resolvers to `app/graphql/resolvers`. Arguments can be defined within the resolver, those arguments will be made available to the fields using the resolver. When exposing a model that had an internal ID (`iid`), prefer using that in combination with the namespace path as arguments in a resolver over a database ID. Otherwise use a [globally unique ID](#exposing-global-ids). We already have a `FullPathLoader` that can be included in other resolvers to quickly find Projects and Namespaces which will have a lot of dependant objects. To limit the amount of queries performed, we can use `BatchLoader`. ## Mutations Mutations are used to change any stored values, or to trigger actions. In the same way a GET-request should not modify data, we cannot modify data in a regular GraphQL-query. We can however in a mutation. To find objects for a mutation, arguments need to be specified. As with [resolvers](#resolvers), prefer using internal ID or, if needed, a global ID rather than the database ID. ### Fields In the most common situations, a mutation would return 2 fields: - The resource being modified - A list of errors explaining why the action could not be performed. If the mutation succeeded, this list would be empty. By inheriting any new mutations from `Mutations::BaseMutation` the `errors` field is automatically added. A `clientMutationId` field is also added, this can be used by the client to identify the result of a single mutation when multiple are performed within a single request. ### Building Mutations Mutations live in `app/graphql/mutations` ideally grouped per resources they are mutating, similar to our services. They should inherit `Mutations::BaseMutation`. The fields defined on the mutation will be returned as the result of the mutation. Always provide a consistent GraphQL-name to the mutation, this name is used to generate the input types and the field the mutation is mounted on. The name should look like ``, for example the `Mutations::MergeRequests::SetWip` mutation has GraphQL name `MergeRequestSetWip`. Arguments required by the mutation can be defined as arguments required for a field. These will be wrapped up in an input type for the mutation. For example, the `Mutations::MergeRequests::SetWip` with GraphQL-name `MergeRequestSetWip` defines these arguments: ```ruby argument :project_path, GraphQL::ID_TYPE, required: true, description: "The project the merge request to mutate is in" argument :iid, GraphQL::STRING_TYPE, required: true, description: "The iid of the merge request to mutate" argument :wip, GraphQL::BOOLEAN_TYPE, required: false, description: <<~DESC Whether or not to set the merge request as a WIP. If not passed, the value will be toggled. DESC ``` This would automatically generate an input type called `MergeRequestSetWipInput` with the 3 arguments we specified and the `clientMutationId`. These arguments are then passed to the `resolve` method of a mutation as keyword arguments. From here, we can call the service that will modify the resource. The `resolve` method should then return a hash with the same field names as defined on the mutation and an `errors` array. For example, the `Mutations::MergeRequests::SetWip` defines a `merge_request` field: ```ruby field :merge_request, Types::MergeRequestType, null: true, description: "The merge request after mutation" ``` This means that the hash returned from `resolve` in this mutation should look like this: ```ruby { # The merge request modified, this will be wrapped in the type # defined on the field merge_request: merge_request, # An array if strings if the mutation failed after authorization errors: merge_request.errors.full_messages } ``` To make the mutation available it should be defined on the mutation type that lives in `graphql/types/mutation_types`. The `mount_mutation` helper method will define a field based on the GraphQL-name of the mutation: ```ruby module Types class MutationType < BaseObject include Gitlab::Graphql::MountMutation graphql_name "Mutation" mount_mutation Mutations::MergeRequests::SetWip end end ``` Will generate a field called `mergeRequestSetWip` that `Mutations::MergeRequests::SetWip` to be resolved. ### Authorizing resources To authorize resources inside a mutation, we first provide the required abilities on the mutation like this: ```ruby module Mutations module MergeRequests class SetWip < Base graphql_name 'MergeRequestSetWip' authorize :update_merge_request end end end ``` We can then call `authorize!` in the `resolve` method, passing in the resource we want to validate the abilities for. Alternatively, we can add a `find_object` method that will load the object on the mutation. This would allow you to use the `authorized_find!` helper method. When a user is not allowed to perform the action, or an object is not found, we should raise a `Gitlab::Graphql::Errors::ResourceNotAvailable` error. Which will be correctly rendered to the clients. ## Validating arguments For validations of single arguments, use the [`prepare` option](https://github.com/rmosolgo/graphql-ruby/blob/master/guides/fields/arguments.md) as normal. Sometimes a mutation or resolver may accept a number of optional arguments, but still want to validate that at least one of the optional arguments were given. In this situation, consider using the `#ready?` method within your mutation or resolver to provide the validation. The `#ready?` method will be called before any work is done within the `#resolve` method. Example: ```ruby def ready?(**args) if args.values_at(:body, :position).compact.blank? raise Gitlab::Graphql::Errors::ArgumentError, 'body or position arguments are required' end # Always remember to call `#super` super(args) end ``` In the future this may be able to be done using `InputUnions` if [this RFC](https://github.com/graphql/graphql-spec/blob/master/rfcs/InputUnion.md) is merged. ## GitLab's custom scalars ### `Types::TimeType` [`Types::TimeType`](https://gitlab.com/gitlab-org/gitlab/blob/master/app%2Fgraphql%2Ftypes%2Ftime_type.rb) must be used as the type for all fields and arguments that deal with Ruby `Time` and `DateTime` objects. The type is [a custom scalar](https://github.com/rmosolgo/graphql-ruby/blob/master/guides/type_definitions/scalars.md#custom-scalars) that: - Converts Ruby's `Time` and `DateTime` objects into standardized ISO-8601 formatted strings, when used as the type for our GraphQL fields. - Converts ISO-8601 formatted time strings into Ruby `Time` objects, when used as the type for our GraphQL arguments. This allows our GraphQL API to have a standardized way that it presents time and handles time inputs. Example: ```ruby field :created_at, Types::TimeType, null: true, description: 'Timestamp of when the issue was created' ``` ## Testing _full stack_ tests for a graphql query or mutation live in `spec/requests/api/graphql`. When adding a query, the `a working graphql query` shared example can be used to test if the query renders valid results. Using the `GraphqlHelpers#all_graphql_fields_for`-helper, a query including all available fields can be constructed. This makes it easy to add a test rendering all possible fields for a query. To test GraphQL mutation requests, `GraphqlHelpers` provides 2 helpers: `graphql_mutation` which takes the name of the mutation, and a hash with the input for the mutation. This will return a struct with a mutation query, and prepared variables. This struct can then be passed to the `post_graphql_mutation` helper, that will post the request with the correct parameters, like a GraphQL client would do. To access the response of a mutation, the `graphql_mutation_response` helper is available. Using these helpers, we can build specs like this: ```ruby let(:mutation) do graphql_mutation( :merge_request_set_wip, project_path: 'gitlab-org/gitlab-foss', iid: '1', wip: true ) end it 'returns a successful response' do post_graphql_mutation(mutation, current_user: user) expect(response).to have_gitlab_http_status(:success) expect(graphql_mutation_response(:merge_request_set_wip)['errors']).to be_empty end ``` ## Notes about Query flow and GraphQL infrastructure GitLab's GraphQL infrastructure can be found in `lib/gitlab/graphql`. [Instrumentation](https://graphql-ruby.org/queries/instrumentation.html) is functionality that wraps around a query being executed. It is implemented as a module that uses the `Instrumentation` class. Example: `Present` ```ruby module Gitlab module Graphql module Present #... some code above... def self.use(schema_definition) schema_definition.instrument(:field, ::Gitlab::Graphql::Present::Instrumentation.new) end end end end ``` A [Query Analyzer](https://graphql-ruby.org/queries/ast_analysis.html#analyzer-api) contains a series of callbacks to validate queries before they are executed. Each field can pass through the analyzer, and the final value is also available to you. [Multiplex queries](https://graphql-ruby.org/queries/multiplex.html) enable multiple queries to be sent in a single request. This reduces the number of requests sent to the server. (there are custom Multiplex Query Analyzers and Multiplex Instrumentation provided by graphql-ruby). ### Query limits Queries and mutations are limited by depth, complexity, and recursion to protect server resources from overly ambitious or malicious queries. These values can be set as defaults and overridden in specific queries as needed. The complexity values can be set per object as well, and the final query complexity is evaluated based on how many objects are being returned. This is useful for objects that are expensive (e.g. requiring Gitaly calls). For example, a conditional complexity method in a resolver: ```ruby def self.resolver_complexity(args, child_complexity:) complexity = super complexity += 2 if args[:labelName] complexity end ``` More about complexity: [graphql-ruby docs](https://graphql-ruby.org/queries/complexity_and_depth.html) ## Documentation and Schema Our schema is located at `app/graphql/gitlab_schema.rb`. See the [schema reference](../api/graphql/reference/index.md) for details. This generated GraphQL documentation needs to be updated when the schema changes. For information on generating GraphQL documentation and schema files, see [updating the schema documentation](rake_tasks.md#update-graphql-documentation-and-schema-definitions).