apollo/README.md

# Apollo CLI

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Apollo CLI brings together your GraphQL clients and servers with tools for validating your schema, linting your operations for compatibility with your server, and generating static types for improved client-side type safety.

<!-- toc -->
* [Apollo CLI](#apollo-cli)
* [Usage](#usage)
* [Commands](#commands)
* [Configuration](#configuration)
* [Code Generation](#code-generation)
* [Contributing](#contributing)
<!-- tocstop -->

# Usage

**Disclaimer**: The following API documentation is only for the latest version released on NPM, and may not be accurate for previous or future versions.

<!-- usage -->
```sh-session
$ npm install -g apollo
$ apollo COMMAND
running command...
$ apollo (-v|--version|version)
apollo/2.31.2 linux-x64 node-v10.23.0
$ apollo --help [COMMAND]
USAGE
  $ apollo COMMAND
...
```
<!-- usagestop -->

# Commands

<!-- commands -->
* [`apollo client:check`](#apollo-clientcheck)
* [`apollo client:codegen [OUTPUT]`](#apollo-clientcodegen-output)
* [`apollo client:download-schema OUTPUT`](#apollo-clientdownload-schema-output)
* [`apollo client:extract OUTPUT`](#apollo-clientextract-output)
* [`apollo client:push`](#apollo-clientpush)
* [`apollo help [COMMAND]`](#apollo-help-command)
* [`apollo plugins`](#apollo-plugins)
* [`apollo plugins:install PLUGIN...`](#apollo-pluginsinstall-plugin)
* [`apollo plugins:link PLUGIN`](#apollo-pluginslink-plugin)
* [`apollo plugins:uninstall PLUGIN...`](#apollo-pluginsuninstall-plugin)
* [`apollo plugins:update`](#apollo-pluginsupdate)
* [`apollo service:check`](#apollo-servicecheck)
* [`apollo service:delete`](#apollo-servicedelete)
* [`apollo service:download OUTPUT`](#apollo-servicedownload-output)
* [`apollo service:list`](#apollo-servicelist)
* [`apollo service:push`](#apollo-servicepush)

## `apollo client:check`

Check a client project against a pushed service

```
USAGE
  $ apollo client:check

OPTIONS
  -c, --config=config                    Path to your Apollo config file

  -g, --graph=graph                      The ID for the graph in Apollo to operate client commands with. Overrides
                                         config file if set.

  -v, --variant=variant                  The variant of the graph in Apollo to associate this client to

  --clientName=clientName                Name of the client that the queries will be attached to

  --clientReferenceId=clientReferenceId  Reference id for the client which will match ids from client traces, will use
                                         clientName if not provided

  --clientVersion=clientVersion          The version of the client that the queries will be attached to

  --endpoint=endpoint                    The URL for the CLI use to introspect your service

  --excludes=excludes                    Glob of files to exclude for GraphQL operations. Caveat: this doesn't currently
                                         work in watch mode

  --header=header                        Additional header to send during introspection. May be used multiple times to
                                         add multiple headers. NOTE: The `--endpoint` flag is REQUIRED if using the
                                         `--header` flag.

  --includes=includes                    Glob of files to search for GraphQL operations. This should be used to find
                                         queries *and* any client schema extensions

  --key=key                              The API key to use for authentication to Apollo

  --queries=queries                      Deprecated in favor of the includes flag

  --tagName=tagName                      Name of the template literal tag used to identify template literals containing
                                         GraphQL queries in Javascript/Typescript code
```

_See code: [src/commands/client/check.ts](https://github.com/apollographql/apollo-tooling/blob/master/packages/apollo/src/commands/client/check.ts)_

## `apollo client:codegen [OUTPUT]`

Generate static types for GraphQL queries. Can use the published schema in the Apollo registry or a downloaded schema.

```
USAGE
  $ apollo client:codegen [OUTPUT]

ARGUMENTS
  OUTPUT
      Directory to which generated files will be written.
      - For TypeScript/Flow generators, this specifies a directory relative to each source file by default.
      - For TypeScript/Flow generators with the "outputFlat" flag is set, and for the Swift generator, this specifies a 
      file or directory (absolute or relative to the current working directory) to which:
         - a file will be written for each query (if "output" is a directory)
         - all generated types will be written
      - For all other types, this defines a file (absolute or relative to the current working directory) to which all 
      generated types are written.

OPTIONS
  -c, --config=config                        Path to your Apollo config file

  -g, --graph=graph                          The ID for the graph in Apollo to operate client commands with. Overrides
                                             config file if set.

  -v, --variant=variant                      The variant of the graph in Apollo to associate this client to

  --[no-]addTypename                         [default: true] Automatically add __typename to your queries, can be unset
                                             with --no-addTypename

  --clientName=clientName                    Name of the client that the queries will be attached to

  --clientReferenceId=clientReferenceId      Reference id for the client which will match ids from client traces, will
                                             use clientName if not provided

  --clientVersion=clientVersion              The version of the client that the queries will be attached to

  --customScalarsPrefix=customScalarsPrefix  Include a prefix when using provided types for custom scalars

  --endpoint=endpoint                        The URL for the CLI use to introspect your service

  --excludes=excludes                        Glob of files to exclude for GraphQL operations. Caveat: this doesn't
                                             currently work in watch mode

  --globalTypesFile=globalTypesFile          By default, TypeScript will put a file named "globalTypes.ts" inside the
                                             "output" directory. Set "globalTypesFile" to specify a different path.
                                             Alternatively, set "tsFileExtension" to modify the extension of the file,
                                             for example "d.ts" will output "globalTypes.d.ts"

  --header=header                            Additional header to send during introspection. May be used multiple times
                                             to add multiple headers. NOTE: The `--endpoint` flag is REQUIRED if using
                                             the `--header` flag.

  --includes=includes                        Glob of files to search for GraphQL operations. This should be used to find
                                             queries *and* any client schema extensions

  --key=key                                  The API key to use for authentication to Apollo

  --localSchemaFile=localSchemaFile          Path to one or more local GraphQL schema file(s), as introspection result
                                             or SDL. Supports comma-separated list of paths (ex.
                                             `--localSchemaFile=schema.graphql,extensions.graphql`)

  --mergeInFieldsFromFragmentSpreads         Merge fragment fields onto its enclosing type

  --namespace=namespace                      The namespace to emit generated code into.

  --omitDeprecatedEnumCases                  Omit deprecated enum cases from generated code [Swift only]

  --only=only                                Parse all input files, but only output generated code for the specified
                                             file [Swift only]

  --operationIdsPath=operationIdsPath        Path to an operation id JSON map file. If specified, also stores the
                                             operation ids (hashes) as properties on operation types [currently
                                             Swift-only]

  --outputFlat                               By default, TypeScript/Flow will put each generated file in a directory
                                             next to its source file using the value of the "output" as the directory
                                             name. Set "outputFlat" to put all generated files in the directory relative
                                             to the current working directory defined by "output".

  --passthroughCustomScalars                 Use your own types for custom scalars

  --queries=queries                          Deprecated in favor of the includes flag

  --suppressSwiftMultilineStringLiterals     Prevents operations from being rendered as multiline strings [Swift only]

  --tagName=tagName                          Name of the template literal tag used to identify template literals
                                             containing GraphQL queries in Javascript/Typescript code

  --target=target                            (required) Type of code generator to use (swift | typescript | flow | scala
                                             | json | json-modern (exposes raw json types))

  --tsFileExtension=tsFileExtension          By default, TypeScript will output "ts" files. Set "tsFileExtension" to
                                             specify a different file extension, for example "d.ts"

  --useFlowExactObjects                      Use Flow exact objects for generated types [flow only]

  --useFlowReadOnlyTypes                     Use read only types for generated types [flow only]. **Deprecated in favor
                                             of `useReadOnlyTypes`.**

  --useReadOnlyTypes                         Use read only types for generated types [flow | typescript]

  --watch                                    Watch for file changes and reload codegen

ALIASES
  $ apollo codegen:generate
```

_See code: [src/commands/client/codegen.ts](https://github.com/apollographql/apollo-tooling/blob/master/packages/apollo/src/commands/client/codegen.ts)_

## `apollo client:download-schema OUTPUT`

Download a schema from Apollo or a GraphQL endpoint in JSON or SDL format

```
USAGE
  $ apollo client:download-schema OUTPUT

ARGUMENTS
  OUTPUT  [default: schema.json] Path to write the introspection result to. Can be `.graphql`, `.gql`, `.graphqls`, or
          `.json`

OPTIONS
  -c, --config=config                    Path to your Apollo config file

  -g, --graph=graph                      The ID for the graph in Apollo to operate client commands with. Overrides
                                         config file if set.

  -v, --variant=variant                  The variant of the graph in Apollo to associate this client to

  --clientName=clientName                Name of the client that the queries will be attached to

  --clientReferenceId=clientReferenceId  Reference id for the client which will match ids from client traces, will use
                                         clientName if not provided

  --clientVersion=clientVersion          The version of the client that the queries will be attached to

  --endpoint=endpoint                    The URL for the CLI use to introspect your service

  --excludes=excludes                    Glob of files to exclude for GraphQL operations. Caveat: this doesn't currently
                                         work in watch mode

  --header=header                        Additional header to send during introspection. May be used multiple times to
                                         add multiple headers. NOTE: The `--endpoint` flag is REQUIRED if using the
                                         `--header` flag.

  --includes=includes                    Glob of files to search for GraphQL operations. This should be used to find
                                         queries *and* any client schema extensions

  --key=key                              The API key to use for authentication to Apollo

  --queries=queries                      Deprecated in favor of the includes flag

  --tagName=tagName                      Name of the template literal tag used to identify template literals containing
                                         GraphQL queries in Javascript/Typescript code
```

_See code: [src/commands/client/download-schema.ts](https://github.com/apollographql/apollo-tooling/blob/master/packages/apollo/src/commands/client/download-schema.ts)_

## `apollo client:extract OUTPUT`

Extract queries from a client

```
USAGE
  $ apollo client:extract OUTPUT

ARGUMENTS
  OUTPUT  [default: manifest.json] Path to write the extracted queries to

OPTIONS
  -c, --config=config                    Path to your Apollo config file

  -g, --graph=graph                      The ID for the graph in Apollo to operate client commands with. Overrides
                                         config file if set.

  -v, --variant=variant                  The variant of the graph in Apollo to associate this client to

  --clientName=clientName                Name of the client that the queries will be attached to

  --clientReferenceId=clientReferenceId  Reference id for the client which will match ids from client traces, will use
                                         clientName if not provided

  --clientVersion=clientVersion          The version of the client that the queries will be attached to

  --endpoint=endpoint                    The URL for the CLI use to introspect your service

  --excludes=excludes                    Glob of files to exclude for GraphQL operations. Caveat: this doesn't currently
                                         work in watch mode

  --header=header                        Additional header to send during introspection. May be used multiple times to
                                         add multiple headers. NOTE: The `--endpoint` flag is REQUIRED if using the
                                         `--header` flag.

  --includes=includes                    Glob of files to search for GraphQL operations. This should be used to find
                                         queries *and* any client schema extensions

  --key=key                              The API key to use for authentication to Apollo

  --preserveStringAndNumericLiterals     Disable redaction of string and numerical literals.  Without this flag, these
                                         values will be replaced with empty strings (`''`) and zeroes (`0`)
                                         respectively.  This redaction is intended to avoid  inadvertently outputting
                                         potentially personally identifiable information (e.g. embedded passwords  or
                                         API keys) into operation manifests

  --queries=queries                      Deprecated in favor of the includes flag

  --tagName=tagName                      Name of the template literal tag used to identify template literals containing
                                         GraphQL queries in Javascript/Typescript code
```

_See code: [src/commands/client/extract.ts](https://github.com/apollographql/apollo-tooling/blob/master/packages/apollo/src/commands/client/extract.ts)_

## `apollo client:push`

Register operations with Apollo, adding them to the safelist

```
USAGE
  $ apollo client:push

OPTIONS
  -c, --config=config                    Path to your Apollo config file

  -g, --graph=graph                      The ID for the graph in Apollo to operate client commands with. Overrides
                                         config file if set.

  -v, --variant=variant                  The variant of the graph in Apollo to associate this client to

  --clientName=clientName                Name of the client that the queries will be attached to

  --clientReferenceId=clientReferenceId  Reference id for the client which will match ids from client traces, will use
                                         clientName if not provided

  --clientVersion=clientVersion          The version of the client that the queries will be attached to

  --endpoint=endpoint                    The URL for the CLI use to introspect your service

  --excludes=excludes                    Glob of files to exclude for GraphQL operations. Caveat: this doesn't currently
                                         work in watch mode

  --header=header                        Additional header to send during introspection. May be used multiple times to
                                         add multiple headers. NOTE: The `--endpoint` flag is REQUIRED if using the
                                         `--header` flag.

  --includes=includes                    Glob of files to search for GraphQL operations. This should be used to find
                                         queries *and* any client schema extensions

  --key=key                              The API key to use for authentication to Apollo

  --queries=queries                      Deprecated in favor of the includes flag

  --tagName=tagName                      Name of the template literal tag used to identify template literals containing
                                         GraphQL queries in Javascript/Typescript code
```

_See code: [src/commands/client/push.ts](https://github.com/apollographql/apollo-tooling/blob/master/packages/apollo/src/commands/client/push.ts)_

## `apollo help [COMMAND]`

display help for apollo

```
USAGE
  $ apollo help [COMMAND]

ARGUMENTS
  COMMAND  command to show help for

OPTIONS
  --all  see all commands in CLI
```

_See code: [@oclif/plugin-help](https://github.com/oclif/plugin-help/blob/v2.2.3/src/commands/help.ts)_

## `apollo plugins`

list installed plugins

```
USAGE
  $ apollo plugins

OPTIONS
  --core  show core plugins

EXAMPLE
  $ apollo plugins
```

_See code: [@oclif/plugin-plugins](https://github.com/oclif/plugin-plugins/blob/v1.9.1/src/commands/plugins/index.ts)_

## `apollo plugins:install PLUGIN...`

installs a plugin into the CLI

```
USAGE
  $ apollo plugins:install PLUGIN...

ARGUMENTS
  PLUGIN  plugin to install

OPTIONS
  -f, --force    yarn install with force flag
  -h, --help     show CLI help
  -v, --verbose

DESCRIPTION
  Can be installed from npm or a git url.

  Installation of a user-installed plugin will override a core plugin.

  e.g. If you have a core plugin that has a 'hello' command, installing a user-installed plugin with a 'hello' command 
  will override the core plugin implementation. This is useful if a user needs to update core plugin functionality in 
  the CLI without the need to patch and update the whole CLI.

ALIASES
  $ apollo plugins:add

EXAMPLES
  $ apollo plugins:install myplugin 
  $ apollo plugins:install https://github.com/someuser/someplugin
  $ apollo plugins:install someuser/someplugin
```

_See code: [@oclif/plugin-plugins](https://github.com/oclif/plugin-plugins/blob/v1.9.1/src/commands/plugins/install.ts)_

## `apollo plugins:link PLUGIN`

links a plugin into the CLI for development

```
USAGE
  $ apollo plugins:link PLUGIN

ARGUMENTS
  PATH  [default: .] path to plugin

OPTIONS
  -h, --help     show CLI help
  -v, --verbose

DESCRIPTION
  Installation of a linked plugin will override a user-installed or core plugin.

  e.g. If you have a user-installed or core plugin that has a 'hello' command, installing a linked plugin with a 'hello' 
  command will override the user-installed or core plugin implementation. This is useful for development work.

EXAMPLE
  $ apollo plugins:link myplugin
```

_See code: [@oclif/plugin-plugins](https://github.com/oclif/plugin-plugins/blob/v1.9.1/src/commands/plugins/link.ts)_

## `apollo plugins:uninstall PLUGIN...`

removes a plugin from the CLI

```
USAGE
  $ apollo plugins:uninstall PLUGIN...

ARGUMENTS
  PLUGIN  plugin to uninstall

OPTIONS
  -h, --help     show CLI help
  -v, --verbose

ALIASES
  $ apollo plugins:unlink
  $ apollo plugins:remove
```

_See code: [@oclif/plugin-plugins](https://github.com/oclif/plugin-plugins/blob/v1.9.1/src/commands/plugins/uninstall.ts)_

## `apollo plugins:update`

update installed plugins

```
USAGE
  $ apollo plugins:update

OPTIONS
  -h, --help     show CLI help
  -v, --verbose
```

_See code: [@oclif/plugin-plugins](https://github.com/oclif/plugin-plugins/blob/v1.9.1/src/commands/plugins/update.ts)_

## `apollo service:check`

Check a service against known operation workloads to find breaking changes

```
USAGE
  $ apollo service:check

OPTIONS
  -c, --config=config                                            Path to your Apollo config file

  -g, --graph=graph                                              The ID of the graph in Apollo to check your proposed
                                                                 schema changes against. Overrides config file if set.

  -v, --variant=variant                                          The variant to check the proposed schema against

  --author=author                                                The author to associate with this proposed schema

  --branch=branch                                                The branch name to associate with this check

  --commitId=commitId                                            The SHA-1 hash of the commit to associate with this
                                                                 check

  --endpoint=endpoint                                            The URL for the CLI use to introspect your service

  --header=header                                                Additional header to send during introspection. May be
                                                                 used multiple times to add multiple headers. NOTE: The
                                                                 `--endpoint` flag is REQUIRED if using the `--header`
                                                                 flag.

  --ignoreFailures                                               Exit with status 0 when the check completes, even if
                                                                 errors are found

  --json                                                         Output result in json, which can then be parsed by CLI
                                                                 tools such as jq.

  --key=key                                                      The API key to use for authentication to Apollo

  --localSchemaFile=localSchemaFile                              Path to one or more local GraphQL schema file(s), as
                                                                 introspection result or SDL. Supports comma-separated
                                                                 list of paths (ex.
                                                                 `--localSchemaFile=schema.graphql,extensions.graphql`)

  --markdown                                                     Output result in markdown.

  --queryCountThreshold=queryCountThreshold                      Minimum number of requests within the requested time
                                                                 window for a query to be considered.

  --queryCountThresholdPercentage=queryCountThresholdPercentage  Number of requests within the requested time window for
                                                                 a query to be considered, relative to total request
                                                                 count. Expected values are between 0 and 0.05 (minimum
                                                                 5% of total request volume)

  --serviceName=serviceName                                      Provides the name of the implementing service for a
                                                                 federated graph. This flag will indicate that the
                                                                 schema is a partial schema from a federated service

  --validationPeriod=validationPeriod                            The size of the time window with which to validate the
                                                                 schema against. You may provide a number (in seconds),
                                                                 or an ISO8601 format duration for more granularity
                                                                 (see: https://en.wikipedia.org/wiki/ISO_8601#Durations)

ALIASES
  $ apollo schema:check
```

_See code: [src/commands/service/check.ts](https://github.com/apollographql/apollo-tooling/blob/master/packages/apollo/src/commands/service/check.ts)_

## `apollo service:delete`

Delete a federated service from Apollo and recompose remaining services

```
USAGE
  $ apollo service:delete

OPTIONS
  -c, --config=config        Path to your Apollo config file

  -g, --graph=graph          The ID of the graph in Apollo for which to delete an implementing service. Overrides config
                             file if set.

  -v, --variant=variant      The variant to delete the implementing service from

  -y, --yes                  Bypass confirmation when deleting a service

  --endpoint=endpoint        The URL for the CLI use to introspect your service

  --header=header            Additional header to send during introspection. May be used multiple times to add multiple
                             headers. NOTE: The `--endpoint` flag is REQUIRED if using the `--header` flag.

  --key=key                  The API key to use for authentication to Apollo

  --serviceName=serviceName  (required) Provides the name of the implementing service for a federated graph
```

_See code: [src/commands/service/delete.ts](https://github.com/apollographql/apollo-tooling/blob/master/packages/apollo/src/commands/service/delete.ts)_

## `apollo service:download OUTPUT`

Download the schema from your GraphQL endpoint.

```
USAGE
  $ apollo service:download OUTPUT

ARGUMENTS
  OUTPUT  [default: schema.json] Path to write the introspection result to. Supports .json output only.

OPTIONS
  -c, --config=config      Path to your Apollo config file

  -g, --graph=graph        The ID of the graph in the Apollo registry for which to download the schema for. Overrides
                           config file if provided.

  -k, --skipSSLValidation  Allow connections to an SSL site without certs

  -v, --variant=variant    The variant to download the schema of

  --endpoint=endpoint      The URL for the CLI use to introspect your service

  --header=header          Additional header to send during introspection. May be used multiple times to add multiple
                           headers. NOTE: The `--endpoint` flag is REQUIRED if using the `--header` flag.

  --key=key                The API key to use for authentication to Apollo

ALIASES
  $ apollo schema:download
```

_See code: [src/commands/service/download.ts](https://github.com/apollographql/apollo-tooling/blob/master/packages/apollo/src/commands/service/download.ts)_

## `apollo service:list`

List the services in a graph

```
USAGE
  $ apollo service:list

OPTIONS
  -c, --config=config    Path to your Apollo config file

  -g, --graph=graph      The ID of the graph in the Apollo registry for which to list implementing services. Overrides
                         config file if set.

  -v, --variant=variant  The variant to list implementing services for

  --endpoint=endpoint    The URL for the CLI use to introspect your service

  --header=header        Additional header to send during introspection. May be used multiple times to add multiple
                         headers. NOTE: The `--endpoint` flag is REQUIRED if using the `--header` flag.

  --key=key              The API key to use for authentication to Apollo
```

_See code: [src/commands/service/list.ts](https://github.com/apollographql/apollo-tooling/blob/master/packages/apollo/src/commands/service/list.ts)_

## `apollo service:push`

Push a service definition to Apollo

```
USAGE
  $ apollo service:push

OPTIONS
  -c, --config=config                Path to your Apollo config file

  -g, --graph=graph                  The ID of the graph in Apollo to publish your service to. Overrides config file if
                                     set.

  -v, --variant=variant              The variant to publish your service to in Apollo

  --author=author                    The author to associate with this publication

  --branch=branch                    The branch name to associate with this publication

  --commitId=commitId                The SHA-1 hash of the commit to associate with this publication

  --endpoint=endpoint                The URL for the CLI use to introspect your service

  --header=header                    Additional header to send during introspection. May be used multiple times to add
                                     multiple headers. NOTE: The `--endpoint` flag is REQUIRED if using the `--header`
                                     flag.

  --key=key                          The API key to use for authentication to Apollo

  --localSchemaFile=localSchemaFile  Path to one or more local GraphQL schema file(s), as introspection result or SDL.
                                     Supports comma-separated list of paths (ex.
                                     `--localSchemaFile=schema.graphql,extensions.graphql`)

  --serviceName=serviceName          Provides the name of the implementing service for a federated graph

  --serviceRevision=serviceRevision  Provides a unique revision identifier for a change to an implementing service on a
                                     federated service push. The default of this is a git sha

  --serviceURL=serviceURL            Provides the url to the location of the implementing service for a federated graph

ALIASES
  $ apollo schema:publish
```

_See code: [src/commands/service/push.ts](https://github.com/apollographql/apollo-tooling/blob/master/packages/apollo/src/commands/service/push.ts)_
<!-- commandsstop -->

# Configuration

The Apollo CLI and VS Code extension can be configured with an Apollo config file. Apollo configuration is stored as a plain object in an `apollo.config.js` file which exports the configuration. For more information about configuring an Apollo project, see: https://www.apollographql.com/docs/devtools/apollo-config/.

> Note: the use of the `apollo` key in the project's package.json file for configuration is deprecated, and will no longer be supported in Apollo v3

You'll need to set up your Apollo configuration for all the features of the Apollo CLI and VS Code extension to work correctly. For full details on how to do that, [visit our docs](https://www.apollographql.com/docs/devtools/apollo-config/). A basic configuration (`apollo.config.js` style) looks something like this:

```js
module.exports = {
  client: {
    name: "My Client Project",
    service: "my-service-name"
  }
};
```

# Code Generation

## Accompanying Libraries

See [Apollo iOS](https://github.com/apollographql/apollo-ios) for details on the mapping from GraphQL results to Swift types, as well as runtime support for executing queries and mutations. For Scala, see [React Apollo Scala.js](https://github.com/apollographql/react-apollo-scalajs) for details on how to use generated Scala code in a Scala.js app with Apollo Client.

## `gql` template support

If the source file for generation is a JavaScript or TypeScript file, the codegen will try to extrapolate the queries inside the [gql tag](https://github.com/apollographql/graphql-tag) templates.

The tag name is configurable using the CLI `--tagName` option.

## Typescript and Flow

When using the codegen command with Typescript or Flow, make sure to add the `__typename` introspection field to every selection set within your graphql operations.

If you're using a client like `apollo-client` that does this automatically for your GraphQL operations, pass in the `--addTypename` option to `apollo codegen:generate` to make sure the generated Typescript and Flow types have the `__typename` field as well. This is required to ensure proper type generation support for `GraphQLUnionType` and `GraphQLInterfaceType` fields.

## Why is the \_\_typename field required?

Using the type information from the GraphQL schema, we can infer the possible types for fields. However, in the case of a `GraphQLUnionType` or `GraphQLInterfaceType`, there are multiple types that are possible for that field. This is best modeled using a disjoint union with the `__typename`
as the discriminant.

For example, given a schema:

```graphql
...

interface Character {
  name: String!
}

type Human implements Character {
  homePlanet: String
}

type Droid implements Character {
  primaryFunction: String
}

...
```

Whenever a field of type `Character` is encountered, it could be either a Human or Droid. Human and Droid objects
will have a different set of fields. Within your application code, when interacting with a `Character` you'll want to make sure to handle both of these cases.

Given this query:

```graphql
query Characters {
  characters(episode: NEW_HOPE) {
    name

    ... on Human {
      homePlanet
    }

    ... on Droid {
      primaryFunction
    }
  }
}
```

Apollo Codegen will generate a union type for Character.

```javascript
export type CharactersQuery = {
  characters: Array<
    | {
        __typename: "Human",
        name: string,
        homePlanet: ?string
      }
    | {
        __typename: "Droid",
        name: string,
        primaryFunction: ?string
      }
  >
};
```

This type can then be used as follows to ensure that all possible types are handled:

```javascript
function CharacterFigures({ characters }: CharactersQuery) {
  return characters.map(character => {
    switch (character.__typename) {
      case "Human":
        return (
          <HumanFigure
            homePlanet={character.homePlanet}
            name={character.name}
          />
        );
      case "Droid":
        return (
          <DroidFigure
            primaryFunction={character.primaryFunction}
            name={character.name}
          />
        );
    }
  });
}
```

# Contributing

[![Build Status](https://circleci.com/gh/apollographql/apollo-tooling.svg?style=svg)](https://circleci.com/gh/apollographql/apollo-tooling)

This repo is composed of multiple packages managed by Lerna. The `apollo-cli` contains the core CLI commands. The `apollo-codegen-core` package contains all the compiler APIs needed to implement code generation support for new languages. The other `apollo-codegen-*` packages implement code generation support for individual languages.

Running tests locally:

```
npm install
npm test
```

You can also run `npm` commands within package folders after you have bootstrapped the repository (part of `npm install`).

> Note: if you have issues, try `npm run clean && npm i` to get a fresh install of the packages. Occasionally problems arise when removed dependencies stay around

## Nock tests

To display the debugging messages for nock, run the following command:

```bash
DEBUG=nock.* npm test
```

It can also be helpful to print standard out during testing. To enable logging, add the following configuration to the `stdout` function call during test creation:

```
.stdout({ print: true })
```

## Active Development / Debugging

To simplify the development process, you may want to step through and debug commands whose behavior you're modifying. To do this, run the executable with node in debug mode like so, where `<command>` is a valid CLI command like `client:check` or `service:push`:

```
node --inspect-brk=9002 packages/apollo/bin/run <command>
```

If you're using VS Code, you can run the included "Attach to CLI Debugger" launch task and debug right from VS Code! Otherwise, you may use the Chrome inspector or [other Node debugger](https://nodejs.org/en/docs/guides/debugging-getting-started/) of your choice.

## Regenerating Mocked Network Data

Some integration tests rely on mocked server data (service:check for example). Mock data is generated by making real network requests and recording those requests with [`nock`'s recording feature](https://github.com/nock/nock#recording). Stop mocking network calls and add `nock.recorder.rec()` before network calls are made. For `service:check`, change `apiKey` to a real Apollo API key. Then run the tests and nock will output code to mock requests to the console. You can (and probably should) pare down the request to be less brittle (by only checking for an operation name, for example). See [`src/commands/service/__tests__/check.test.ts`](./packages/apollo/src/commands/service/__tests__/check.test.ts) for an example of how a mocked network request will look.


## Publishing

1. Make sure the `CHANGELOG.md` is updated with all changes committed since the last release. Make sure the versions for each package to update are correct, and there's a blank `Upcoming` section for future work.
2. Run `npm run release:version-bump -- <bumpish>`
   - Can use major, minor, patch, prepatch, etc for the bump type. If not used, the command will prompt and ask for the bump type.
   - This command updates git tags locally and on GitHub
3. Run npm run release:start-ci-publish locally
   - Pushes a `publish/XXXXXXXXXX` tag to GitHub to trigger circle CI build
4. Circle will notify the appropriate Apollo team slack channel when ready to release
   - Slack channel member will confirm through the Apollo Deploy Bot
   - Circle will release to all channels (npm, cli binary to s3, vscode marketplace)
   - Another slack bot notification will confirm success of release.

## Maintainers

- [@JakeDawkins](https://github.com/jakedawkins) (Apollo)