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# frozen-string-literal: true
#
# The query extension adds a query method which allows
# a different way to construct queries instead of the usual
# method chaining:
#
# dataset = DB[:items].query do
# select :x, :y, :z
# where{(x > 1) & (y > 2)}
# reverse :z
# end
#
# You can load this extension into specific datasets:
#
# ds = DB[:table]
# ds = ds.extension(:query)
#
# Or you can load it into all of a database's datasets, which
# is probably the desired behavior if you are using this extension:
#
# DB.extension(:query)
#
# Related modules: Sequel::DatabaseQuery, Sequel::DatasetQuery,
# Sequel::Dataset::Query
#
module Sequel
module DatabaseQuery
def self.extended(db)
db.extend_datasets(DatasetQuery)
end
# Return a dataset modified by the query block
def query(&block)
dataset.query(&block)
end
end
module DatasetQuery
# Translates a query block into a dataset. Query blocks are an
# alternative to Sequel's usual method chaining, by using
# instance_exec with a proxy object:
#
# dataset = DB[:items].query do
# select :x, :y, :z
# where{(x > 1) & (y > 2)}
# reverse :z
# end
#
# Which is the same as:
#
# dataset = DB[:items].select(:x, :y, :z).where{(x > 1) & (y > 2)}.reverse(:z)
def query(&block)
query = Dataset::Query.new(self)
query.instance_exec(&block)
query.dataset
end
end
class Dataset
# Proxy object used by Dataset#query.
class Query < Sequel::BasicObject
# The current dataset in the query. This changes on each method call.
attr_reader :dataset
def initialize(dataset)
@dataset = dataset
end
# Replace the query's dataset with dataset returned by the method call.
def method_missing(method, *args, &block)
# Allow calling private methods, so things like raise works
@dataset = @dataset.send(method, *args, &block)
raise(Sequel::Error, "method #{method.inspect} did not return a dataset") unless @dataset.is_a?(Dataset)
self
end
# :nocov:
ruby2_keywords(:method_missing) if respond_to?(:ruby2_keywords, true)
# :nocov:
end
end
Dataset.register_extension(:query, DatasetQuery)
Database.register_extension(:query, DatabaseQuery)
end
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