mastodon/app/models/concerns/status_safe_reblog_insert.rb

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# frozen_string_literal: true
module StatusSafeReblogInsert
extend ActiveSupport::Concern
class_methods do
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# This patch overwrites the built-in ActiveRecord `_insert_record` method to
# ensure that no reblogs of discarded statuses are created, as this cannot be
# enforced through DB constraints the same way as reblogs of deleted statuses
#
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# We redefine the internal method responsible for issuing the `INSERT`
# statement and replace the `INSERT INTO ... VALUES ...` query with an `INSERT
# INTO ... SELECT ...` query with a `WHERE deleted_at IS NULL` clause on the
# reblogged status to ensure consistency at the database level.
#
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# The code is kept similar to ActiveRecord::Persistence code and calls it
# directly when we are not handling a reblog.
def _insert_record(values)
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return super unless values.is_a?(Hash) && values['reblog_of_id']&.value.present?
primary_key = self.primary_key
primary_key_value = nil
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if prefetch_primary_key? && primary_key
values[primary_key] ||= begin
primary_key_value = next_sequence_value
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_default_attributes[primary_key].with_cast_value(primary_key_value)
end
end
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# The following line departs from stock ActiveRecord
# Original code was:
# im.insert(values.transform_keys { |name| arel_table[name] })
# Instead, we use a custom builder when a reblog is happening:
im = _compile_reblog_insert(values)
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connection.insert(im, "#{self} Create", primary_key || false, primary_key_value).tap do |result|
# Since we are using SELECT instead of VALUES, a non-error `nil` return is possible.
# For our purposes, it's equivalent to a foreign key constraint violation
raise ActiveRecord::InvalidForeignKey, "(reblog_of_id)=(#{values['reblog_of_id'].value}) is not present in table \"statuses\"" if result.nil?
end
end
def _compile_reblog_insert(values)
# This is somewhat equivalent to the following code of ActiveRecord::Persistence:
# `arel_table.compile_insert(_substitute_values(values))`
# The main difference is that we use a `SELECT` instead of a `VALUES` clause,
# which means we have to build the `SELECT` clause ourselves and do a bit more
# manual work.
# Instead of using Arel::InsertManager#values, we are going to use Arel::InsertManager#select
im = Arel::InsertManager.new
im.into(arel_table)
binds = []
reblog_bind = nil
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values.each do |name, attribute|
attr = arel_table[name]
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bind = predicate_builder.build_bind_attribute(attr.name, attribute.value)
im.columns << attr
binds << bind
reblog_bind = bind if name == 'reblog_of_id'
end
im.select(arel_table.where(arel_table[:id].eq(reblog_bind)).where(arel_table[:deleted_at].eq(nil)).project(*binds))
im
end
end
end