144 lines
4.4 KiB
Ruby
144 lines
4.4 KiB
Ruby
# frozen_string_literal: true
|
|
|
|
# Concern that will eliminate N+1 queries for size-constrained
|
|
# collections of items.
|
|
#
|
|
# **note**: The resolver will never load more items than
|
|
# `@field.max_page_size` if defined, falling back to
|
|
# `context.schema.default_max_page_size`.
|
|
#
|
|
# provided that:
|
|
#
|
|
# - the query can be uniquely determined by the object and the arguments
|
|
# - the model class includes FromUnion
|
|
# - the model class defines a scalar primary key
|
|
#
|
|
# This comes at the cost of returning arrays, not relations, so we don't get
|
|
# any keyset pagination goodness. Consequently, this is only suitable for small-ish
|
|
# result sets, as the full result set will be loaded into memory.
|
|
#
|
|
# To enforce this, the resolver limits the size of result sets to
|
|
# `@field.max_page_size || context.schema.default_max_page_size`.
|
|
#
|
|
# **important**: If the cardinality of your collection is likely to be greater than 100,
|
|
# then you will want to pass `max_page_size:` as part of the field definition
|
|
# or (ideally) as part of the resolver `field_options`.
|
|
#
|
|
# How to implement:
|
|
# --------------------
|
|
#
|
|
# Each including class operates on two generic parameters, A and R:
|
|
# - A is any Object that can be used as a Hash key. Instances of A
|
|
# are returned by `query_input` and then passed to `query_for`.
|
|
# - R is any subclass of ApplicationRecord that includes FromUnion.
|
|
# R must have a single scalar primary_key
|
|
#
|
|
# Classes must implement:
|
|
# - #model_class -> Class[R]. (Must respond to :primary_key, and :from_union)
|
|
# - #query_input(**kwargs) -> A (Must be hashable)
|
|
# - #query_for(A) -> ActiveRecord::Relation[R]
|
|
#
|
|
# Note the relationship between query_input and query_for, one of which
|
|
# consumes the input of the other
|
|
# (i.e. `resolve(**args).sync == query_for(query_input(**args)).to_a`).
|
|
#
|
|
# Classes may implement:
|
|
# - max_union_size Integer (the maximum number of queries to run in any one union)
|
|
# - preload -> Preloads|NilClass (a set of preloads to apply to each query)
|
|
# - #item_found(A, R) (return value is ignored)
|
|
# - allowed?(R) -> Boolean (if this method returns false, the value is not resolved)
|
|
module CachingArrayResolver
|
|
MAX_UNION_SIZE = 50
|
|
|
|
def resolve(**args)
|
|
key = query_input(**args)
|
|
|
|
BatchLoader::GraphQL.for(key).batch(**batch) do |keys, loader|
|
|
if keys.size == 1
|
|
# We can avoid the union entirely.
|
|
k = keys.first
|
|
limit(query_for(k)).each { |item| found(loader, k, item) }
|
|
else
|
|
queries = keys.map { |key| query_for(key) }
|
|
|
|
queries.in_groups_of(max_union_size, false).each do |group|
|
|
by_id = model_class
|
|
.select(all_fields, :union_member_idx)
|
|
.from_union(tag(group), remove_duplicates: false)
|
|
.preload(preload) # rubocop: disable CodeReuse/ActiveRecord
|
|
.group_by { |r| r[primary_key] }
|
|
|
|
by_id.values.each do |item_group|
|
|
item = item_group.first
|
|
item_group.map(&:union_member_idx).each do |i|
|
|
found(loader, keys[i], item)
|
|
end
|
|
end
|
|
end
|
|
end
|
|
end
|
|
end
|
|
|
|
# Override to apply filters on a per-item basis
|
|
def allowed?(item)
|
|
true
|
|
end
|
|
|
|
# Override to specify preloads for each query
|
|
def preload
|
|
nil
|
|
end
|
|
|
|
# Override this to intercept the items once they are found
|
|
def item_found(query_input, item)
|
|
end
|
|
|
|
def max_union_size
|
|
MAX_UNION_SIZE
|
|
end
|
|
|
|
private
|
|
|
|
def primary_key
|
|
@primary_key ||= (model_class.primary_key || raise("No primary key for #{model_class}"))
|
|
end
|
|
|
|
def batch
|
|
{ key: self.class, default_value: [] }
|
|
end
|
|
|
|
def found(loader, key, value)
|
|
return unless allowed?(value)
|
|
|
|
loader.call(key) do |vs|
|
|
item_found(key, value)
|
|
vs << value
|
|
end
|
|
end
|
|
|
|
# Tag each row returned from each query with a the index of which query in
|
|
# the union it comes from. This lets us map the results back to the cache key.
|
|
def tag(queries)
|
|
queries.each_with_index.map do |q, i|
|
|
limit(q.select(all_fields, member_idx(i)))
|
|
end
|
|
end
|
|
|
|
def limit(query)
|
|
query.limit(query_limit) # rubocop: disable CodeReuse/ActiveRecord
|
|
end
|
|
|
|
def all_fields
|
|
model_class.arel_table[Arel.star]
|
|
end
|
|
|
|
# rubocop: disable Graphql/Descriptions (false positive!)
|
|
def query_limit
|
|
field&.max_page_size.presence || context.schema.default_max_page_size
|
|
end
|
|
# rubocop: enable Graphql/Descriptions
|
|
|
|
def member_idx(idx)
|
|
::Arel::Nodes::SqlLiteral.new(idx.to_s).as('union_member_idx')
|
|
end
|
|
end
|