Class: GraphQL::Dataloader::Source

Inherits:
Object
  • Object
show all
Defined in:
lib/graphql/dataloader/source.rb

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#dataloader ⇒ Object (readonly)

Returns the value of attribute dataloader.



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# File 'lib/graphql/dataloader/source.rb', line 18

def dataloader
  @dataloader
end

#pending ⇒ Object (readonly)

Returns the value of attribute pending.



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# File 'lib/graphql/dataloader/source.rb', line 164

def pending
  @pending
end

Class Method Details

.batch_key_for(*batch_args, **batch_kwargs) ⇒ Object

These arguments are given to dataloader.with(source_class, ...). The object returned from this method is used to de-duplicate batch loads under the hood by using it as a Hash key.

By default, the arguments are all put in an Array. To customize how this source’s batches are merged, override this method to return something else.

For example, if you pass ActiveRecord::Relations to .with(...), you could override this method to call .to_sql on them, thus merging .load(...) calls when they apply to equivalent relations.

Parameters:

  • batch_args (Array<Object>)
  • batch_kwargs (Hash)

Returns:

  • (Object) 


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# File 'lib/graphql/dataloader/source.rb', line 160

def self.batch_key_for(*batch_args, **batch_kwargs)
  [*batch_args, **batch_kwargs]
end

Instance Method Details

#fetch(keys) ⇒ Array<Object>

Subclasses must implement this method to return a value for each of keys

Parameters:

Returns:

  • (Array<Object>) —

    A loaded value for each of keys. The array must match one-for-one to the list of keys.



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# File 'lib/graphql/dataloader/source.rb', line 86

def fetch(keys)
  # somehow retrieve these from the backend
  raise "Implement `#{self.class}#fetch(#{keys.inspect}) to return a record for each of the keys"
end

#load(value) ⇒ Object

Returns The result from #fetch for key. If key hasn’t been loaded yet, the Fiber will yield until it’s loaded.

Parameters:

  • value (Object) —

    A loading value which will be passed to #fetch if it isn’t already in the internal cache.

Returns:

  • (Object) —

    The result from #fetch for key. If key hasn’t been loaded yet, the Fiber will yield until it’s loaded.



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# File 'lib/graphql/dataloader/source.rb', line 51

def load(value)
  result_key = result_key_for(value)
  if @results.key?(result_key)
    result_for(result_key)
  else
    @pending[result_key] ||= value
    sync([result_key])
    result_for(result_key)
  end
end

#load_all(values) ⇒ Object

Returns The result from #fetch for keys. If keys haven’t been loaded yet, the Fiber will yield until they’re loaded.

Parameters:

  • values (Array<Object>) —

    Loading keys which will be passed to #fetch (or read from the internal cache).

Returns:

  • (Object) —

    The result from #fetch for keys. If keys haven’t been loaded yet, the Fiber will yield until they’re loaded.



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# File 'lib/graphql/dataloader/source.rb', line 64

def load_all(values)
  result_keys = []
  pending_keys = []
  values.each { |v|
    k = result_key_for(v)
    result_keys << k
    if !@results.key?(k)
      @pending[k] ||= v
      pending_keys << k
    end
  }

  if pending_keys.any?
    sync(pending_keys)
  end

  result_keys.map { |k| result_for(k) }
end

#merge(new_results) ⇒ void

This method returns an undefined value.

Add these key-value pairs to this source’s cache (future loads will use these merged values).

Parameters:

  • new_results (Hash<Object => Object>) —

    key-value pairs to cache in this source



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# File 'lib/graphql/dataloader/source.rb', line 116

def merge(new_results)
  new_results.each do |new_k, new_v|
    key = result_key_for(new_k)
    @results[key] = new_v
  end
  nil
end

#pending? ⇒ Boolean

Returns True if this source has any pending requests for data.

Returns:

  • (Boolean) —

    True if this source has any pending requests for data.



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# File 'lib/graphql/dataloader/source.rb', line 108

def pending?
  !@pending.empty?
end

#request(value) ⇒ Dataloader::Request

Returns a pending request for a value from key. Call .load on that object to wait for the result.

Returns:

  • (Dataloader::Request) —

    a pending request for a value from key. Call .load on that object to wait for the result.



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# File 'lib/graphql/dataloader/source.rb', line 21

def request(value)
  res_key = result_key_for(value)
  if !@results.key?(res_key)
    @pending[res_key] ||= value
  end
  Dataloader::Request.new(self, value)
end

#request_all(values) ⇒ Dataloader::Request

Returns a pending request for a values from keys. Call .load on that object to wait for the results.

Returns:

  • (Dataloader::Request) —

    a pending request for a values from keys. Call .load on that object to wait for the results.



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# File 'lib/graphql/dataloader/source.rb', line 39

def request_all(values)
  values.each do |v|
    res_key = result_key_for(v)
    if !@results.key?(res_key)
      @pending[res_key] ||= v
    end
  end
  Dataloader::RequestAll.new(self, values)
end

#result_key_for(value) ⇒ Object

Implement this method to return a stable identifier if different key objects should load the same data value.

Parameters:

  • value (Object) —

    A value passed to .request or .load, for which a value will be loaded

Returns:

  • (Object) —

    The key for tracking this pending data



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# File 'lib/graphql/dataloader/source.rb', line 34

def result_key_for(value)
  value
end

#run_pending_keys ⇒ void

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

This method returns an undefined value.

Called by GraphQL::Dataloader to resolve and pending requests to this source.



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# File 'lib/graphql/dataloader/source.rb', line 127

def run_pending_keys
  if !@fetching.empty?
    @fetching.each_key { |k| @pending.delete(k) }
  end
  return if @pending.empty?
  fetch_h = @pending
  @pending = {}
  @fetching.merge!(fetch_h)
  results = fetch(fetch_h.values)
  fetch_h.each_with_index do |(key, _value), idx|
    @results[key] = results[idx]
  end
  nil
rescue StandardError => error
  fetch_h.each_key { |key| @results[key] = error }
ensure
  fetch_h && fetch_h.each_key { |k| @fetching.delete(k) }
end

#setup(dataloader) ⇒ Object

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Called by GraphQL::Dataloader to prepare the GraphQL::Dataloader::Source’s internal state



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# File 'lib/graphql/dataloader/source.rb', line 8

def setup(dataloader)
  # These keys have been requested but haven't been fetched yet
  @pending = {}
  # These keys have been passed to `fetch` but haven't been finished yet
  @fetching = {}
  # { key => result }
  @results = {}
  @dataloader = dataloader
end

#sync(pending_result_keys) ⇒ void

This method returns an undefined value.

Wait for a batch, if there’s anything to batch. Then run the batch and update the cache.



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# File 'lib/graphql/dataloader/source.rb', line 94

def sync(pending_result_keys)
  @dataloader.yield
  iterations = 0
  while pending_result_keys.any? { |key| !@results.key?(key) }
    iterations += 1
    if iterations > 1000
      raise "#{self.class}#sync tried 1000 times to load pending keys (#{pending_result_keys}), but they still weren't loaded. There is likely a circular dependency."
    end
    @dataloader.yield
  end
  nil
end