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https://github.com/DmitryTsepelev/graphql-ruby-fragment_cache

graphql-ruby plugin for caching parts of the response
https://github.com/DmitryTsepelev/graphql-ruby-fragment_cache

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graphql-ruby plugin for caching parts of the response

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# GraphQL::FragmentCache ![CI](https://github.com/DmitryTsepelev/graphql-ruby-fragment_cache/actions/workflows/rspec.yml/badge.svg?branch=master) ![](https://ruby-gem-downloads-badge.herokuapp.com/graphql-fragment_cache?type=total)



`GraphQL::FragmentCache` powers up [graphql-ruby](https://graphql-ruby.org) with the ability to cache response _fragments_: you can mark any field as cached and it will never be resolved again (at least, while cache is valid). For instance, the following code caches `title` for each post:



```ruby

class PostType < BaseObject

  field :id, ID, null: false

  field :title, String, null: false, cache_fragment: true

end

```



You can support my open–source work [here](https://boosty.to/dmitry_tsepelev).



## Getting started



Add the gem to your Gemfile `gem 'graphql-fragment_cache'` and add the plugin to your schema class:



```ruby

class GraphqSchema < GraphQL::Schema

  use GraphQL::FragmentCache



  query QueryType

end

```



Include `GraphQL::FragmentCache::Object` to your base type class:



```ruby

class BaseType < GraphQL::Schema::Object

  include GraphQL::FragmentCache::Object

end

```



If you're using [resolvers](https://graphql-ruby.org/fields/resolvers.html) — include the module into the base resolver as well:



```ruby

class Resolvers::BaseResolver < GraphQL::Schema::Resolver

  include GraphQL::FragmentCache::ObjectHelpers

end

```



Now you can add `cache_fragment:` option to your fields to turn caching on:



```ruby

class PostType < BaseObject

  field :id, ID, null: false

  field :title, String, null: false, cache_fragment: true

end

```



Alternatively, you can use `cache_fragment` method inside resolver methods:



```ruby

class QueryType < BaseObject

  field :post, PostType, null: true do

    argument :id, ID, required: true

  end



  def post(id:)

    cache_fragment { Post.find(id) }

  end

end

```



## Cache key generation



Cache keys consist of the following parts: namespace, implicit key, and explicit key.



### Cache namespace



The namespace is prefixed to every cached key. The default namespace is `graphql`, which is configurable:



```ruby

GraphQL::FragmentCache.namespace = "graphql"

```



### Implicit cache key



Implicit part of a cache key contains the information about the schema and the current query. It includes:



- Hex gsdigest of the schema definition (to make sure cache is cleared when the schema changes).

- The current query fingerprint consisting of a _path_ to the field, arguments information and the selections set.



Let's take a look at the example:



```ruby

query = <<~GQL

  query {

    post(id: 1) {

      id

      title

      cachedAuthor {

        id

        name

      }

    }

  }

GQL



schema_cache_key = GraphqSchema.schema_cache_key



path_cache_key = "post(id:1)/cachedAuthor"

selections_cache_key = "[#{%w[id name].join(".")}]"



query_cache_key = Digest::SHA1.hexdigest("#{path_cache_key}#{selections_cache_key}")



cache_key = "#{schema_cache_key}/#{query_cache_key}/#{object_cache_key}"

```



You can override `schema_cache_key`, `query_cache_key`, `path_cache_key` or `object_cache_key` by passing parameters to the `cache_fragment` calls:



```ruby

class QueryType < BaseObject

  field :post, PostType, null: true do

    argument :id, ID, required: true

  end



  def post(id:)

    cache_fragment(query_cache_key: "post(#{id})") { Post.find(id) }

  end

end

```



Overriding `path_cache_key` might be helpful when you resolve the same object nested in multiple places (e.g., `Post` and `Comment` both have `author`), but want to make sure cache will be invalidated when selection set is different.



Same for the option:



```ruby

class PostType < BaseObject

  field :id, ID, null: false

  field :title, String, null: false, cache_fragment: {query_cache_key: "post_title"}

end

```



Overriding `object_cache_key` is helpful in the case where the value that is cached is different than the one used as a key, like a database query that is pre-processed before caching.



```ruby

class QueryType < BaseObject

  field :post, PostType, null: true do

    argument :id, ID, required: true

  end



  def post(id:)

    query = Post.where("updated_at < ?", Time.now - 1.day)

    cache_fragment(object_cache_key: query.cache_key) { query.some_process }

  end

end

```



### User-provided cache key (custom key)



In most cases you want your cache key to depend on the resolved object (say, `ActiveRecord` model). You can do that by passing an argument to the `#cache_fragment` method in a similar way to Rails views [`#cache` method](https://guides.rubyonrails.org/caching_with_rails.html#fragment-caching):



```ruby

def post(id:)

  post = Post.find(id)

  cache_fragment(post) { post }

end

```



You can pass arrays as well to build a compound cache key:



```ruby

def post(id:)

  post = Post.find(id)

  cache_fragment([post, current_account]) { post }

end

```



You can omit the block if its return value is the same as the cached object:



```ruby

# the following line

cache_fragment(post)

# is the same as

cache_fragment(post) { post }

```



Using literals: Even when using a same string for all queries, the cache changes per argument and per selection set (because of the query_key).



```ruby

def post(id:)

  cache_fragment("find_post") { Post.find(id) }

end

```



Combining with options:



```ruby

def post(id:)

  cache_fragment("find_post", expires_in: 5.minutes) { Post.find(id) }

end

```



Dynamic cache key:



```ruby

def post(id:)

  last_updated_at = Post.select(:updated_at).find_by(id: id)&.updated_at

  cache_fragment(last_updated_at, expires_in: 5.minutes) { Post.find(id) }

end

```



Note the usage of `.select(:updated_at)` at the cache key field to make this verifying query as fastest and light as possible.



You can also add touch options for the belongs_to association e.g author's `belongs_to: :post` to have a `touch: true`.

So that it invalidates the Post when the author is updated.



When using `cache_fragment:` option, it's only possible to use the resolved value as a cache key by setting:



```ruby

field :post, PostType, null: true, cache_fragment: {cache_key: :object} do

  argument :id, ID, required: true

end



# this is equal to

def post(id:)

  cache_fragment(Post.find(id))

end

```



Also, you can pass `:value` to the `cache_key:` argument to use the returned value to build a key:



```ruby

field :post, PostType, null: true, cache_fragment: {cache_key: :value} do

  argument :id, ID, required: true

end



# this is equal to

def post(id:)

  post = Post.find(id)

  cache_fragment(post) { post }

end

```



If you need more control, you can set `cache_key:` to any custom code:



```ruby

field :posts,

  Types::Objects::PostType.connection_type,

  cache_fragment: {cache_key: -> { object.posts.maximum(:created_at) }}

```



The way cache key part is generated for the passed argument is the following:



- Use `object_cache_key: "some_cache_key"` if passed to `cache_fragment`

- Use `#graphql_cache_key` if implemented.

- Use `#cache_key` (or `#cache_key_with_version` for modern Rails) if implemented.

- Use `self.to_s` for _primitive_ types (strings, symbols, numbers, booleans).

- Raise `ArgumentError` if none of the above.



### Context cache key



By default, we do not take context into account when calculating cache keys. That's because caching is more efficient when it's _context-free_.



However, if you want some fields to be cached per context, you can do that either by passing context objects directly to the `#cache_fragment` method (see above) or by adding a `context_key` option to `cache_fragment:`.



For instance, imagine a query that allows the current user's social profiles:



```gql

query {

  socialProfiles {

    provider

    id

  }

}

```



You can cache the result using the context (`context[:user]`) as a cache key:



```ruby

class QueryType < BaseObject

  field :social_profiles, [SocialProfileType], null: false, cache_fragment: {context_key: :user}



  def social_profiles

    context[:user].social_profiles

  end

end

```



This is equal to using `#cache_fragment` the following way:



```ruby

class QueryType < BaseObject

  field :social_profiles, [SocialProfileType], null: false



  def social_profiles

    cache_fragment(context[:user]) { context[:user].social_profiles }

  end

end

```



## Conditional caching



Use the `if:` (or `unless:`) option:



```ruby

def post(id:)

  cache_fragment(if: current_user.nil?) { Post.find(id) }

end



# or



field :post, PostType, cache_fragment: {if: -> { current_user.nil? }} do

  argument :id, ID, required: true

end



# or



field :post, PostType, cache_fragment: {if: :current_user?} do

  argument :id, ID, required: true

end

```



## Default options



You can configure default options that will be passed to all `cache_fragment`

calls and `cache_fragment:` configurations. For example:



```ruby

GraphQL::FragmentCache.configure do |config|

  config.default_options = {

    expires_in: 1.hour, # Expire cache keys after 1 hour

    schema_cache_key: nil # Do not clear the cache on each schema change

  }

end

```



## Renewing the cache



You can force the cache to renew during query execution by adding

`renew_cache: true` to the query context:



```ruby

MyAppSchema.execute("query { posts { title } }", context: {renew_cache: true})

```



This will treat any cached value as missing even if it's present, and store

fresh new computed values in the cache. This can be useful for cache warmers.



## Cache storage and options



It's up to your to decide which caching engine to use, all you need is to configure the cache store:



```ruby

GraphQL::FragmentCache.configure do |config|

  config.cache_store = MyCacheStore.new

end

```



Or, in Rails:



```ruby

# config/application.rb (or config/environments/.rb)

Rails.application.configure do |config|

  # arguments and options are the same as for `config.cache_store`

  config.graphql_fragment_cache.store = :redis_cache_store

end

```



⚠️ Cache store must implement `#read(key)`, `#exist?(key)` and `#write_multi(hash, **options)` or `#write(key, value, **options)` methods.



The gem provides only in-memory store out-of-the-box (`GraphQL::FragmentCache::MemoryStore`). It's used by default.



You can pass store-specific options to `#cache_fragment` or `cache_fragment:`. For example, to set expiration (assuming the store's `#write` method supports `expires_in` option):



```ruby

class PostType < BaseObject

  field :id, ID, null: false

  field :title, String, null: false, cache_fragment: {expires_in: 5.minutes}

end



class QueryType < BaseObject

  field :post, PostType, null: true do

    argument :id, ID, required: true

  end



  def post(id:)

    cache_fragment(expires_in: 5.minutes) { Post.find(id) }

  end

end

```



## How to use `#cache_fragment` in extensions (and other places where context is not available)



If you want to call `#cache_fragment` from places other that fields or resolvers, you'll need to pass `context` explicitly and turn on `raw_value` support. For instance, let's take a look at this extension:



```ruby

class Types::QueryType < Types::BaseObject

  class CurrentMomentExtension < GraphQL::Schema::FieldExtension

    # turning on cache_fragment support

    include GraphQL::FragmentCache::ObjectHelpers



    def resolve(object:, arguments:, context:)

      # context is passed explicitly

      cache_fragment(context: context) do

        result = yield(object, arguments)

        "#{result} (at #{Time.now})"

      end

    end

  end



  field :event, String, null: false, extensions: [CurrentMomentExtension]



  def event

    "something happened"

  end

end

```



With this approach you can use `#cache_fragment` in any place you have an access to the `context`. When context is not available, the error `cannot find context, please pass it explicitly` will be thrown.



## In–memory fragments



If you have a fragment that accessed from multiple times (e.g., if you have a list of items that belong to the same owner, and owner is cached), you can avoid multiple cache reads by using `:keep_in_context` option:



```ruby

class QueryType < BaseObject

  field :post, PostType, null: true do

    argument :id, ID, required: true

  end



  def post(id:)

    cache_fragment(keep_in_context: true, expires_in: 5.minutes) { Post.find(id) }

  end

end

```



This can reduce a number of cache calls but _increase_ memory usage, because the value returned from cache will be kept in the GraphQL context until the query is fully resolved.



## Execution errors and caching



Sometimes errors happen during query resolving and it might make sense to skip caching for such queries (for instance, imagine a situation when client has no access to the requested field and the backend returns `{ data: {}, errors: ["you need a permission to fetch orders"] }`). This is how this behavior can be turned on (_it's off by default!_):



```ruby

GraphQL::FragmentCache.skip_cache_when_query_has_errors = true

```



As a result, caching will be skipped when `errors` array is not empty.



## Disabling the cache



Cache processing can be disabled if needed. For example:



```ruby

GraphQL::FragmentCache.enabled = false if Rails.env.test?

```



## Limitations



1. `Schema#execute`, [graphql-batch](https://github.com/Shopify/graphql-batch) and _graphql-ruby-fragment_cache_ do not [play well](https://github.com/DmitryTsepelev/graphql-ruby-fragment_cache/issues/45) together. The problem appears when `cache_fragment` is _inside_ the `.then` block:



```ruby

def cached_author_inside_batch

  AuthorLoader.load(object).then do |author|

    cache_fragment(author, context: context)

  end

end

```



The problem is that context is not [properly populated](https://github.com/rmosolgo/graphql-ruby/issues/3397) inside the block (the gem uses `:current_path` to build the cache key). There are two possible workarounds: use [dataloaders](https://graphql-ruby.org/dataloader/overview.html) or manage `:current_path` manually:



```ruby

def cached_author_inside_batch

  outer_path = context.namespace(:interpreter)[:current_path]



  AuthorLoader.load(object).then do |author|

    context.namespace(:interpreter)[:current_path] = outer_path

    cache_fragment(author, context: context)

  end

end

```



2. Caching does not work for Union types, because of the `Lookahead` implementation: it requires the exact type to be passed to the `selection` method (you can find the [discussion](https://github.com/rmosolgo/graphql-ruby/pull/3007) here). This method is used for cache key building, and I haven't found a workaround yet ([PR in progress](https://github.com/DmitryTsepelev/graphql-ruby-fragment_cache/pull/30)). If you get `Failed to look ahead the field` error — please pass `path_cache_key` explicitly:



```ruby

field :cached_avatar_url, String, null: false



def cached_avatar_url

  cache_fragment(query_cache_key: "post_avatar_url(#{object.id})") { object.avatar_url }

end

```



## Credits



Based on the original [gist](https://gist.github.com/palkan/faad9f6ff1db16fcdb1c071ec50e4190) by [@palkan](https://github.com/palkan) and [@ssnickolay](https://github.com/ssnickolay).



Initially sponsored by [Evil Martians](http://evilmartians.com).



## Contributing



Bug reports and pull requests are welcome on GitHub at [https://github.com/DmitryTsepelev/graphql-ruby-fragment_cache](https://github.com/DmitryTsepelev/graphql-ruby-fragment_cache).



## License



The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT).