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# frozen-string-literal: true
module Sequel
class Database
# ---------------------
# :section: 3 - Methods that create datasets
# These methods all return instances of this database's dataset class.
# ---------------------
# Returns a dataset for the database. If the first argument is a string,
# the method acts as an alias for Database#fetch, returning a dataset for
# arbitrary SQL, with or without placeholders:
#
# DB['SELECT * FROM items'].all
# DB['SELECT * FROM items WHERE name = ?', my_name].all
#
# Otherwise, acts as an alias for Database#from, setting the primary
# table for the dataset:
#
# DB[:items].sql #=> "SELECT * FROM items"
def [](*args)
args.first.is_a?(String) ? fetch(*args) : from(*args)
end
# Returns a blank dataset for this database.
#
# DB.dataset # SELECT *
# DB.dataset.from(:items) # SELECT * FROM items
def dataset
@dataset_class.new(self)
end
# Returns a dataset instance for the given SQL string:
#
# ds = DB.fetch('SELECT * FROM items')
#
# You can then call methods on the dataset to retrieve results:
#
# ds.all
# # SELECT * FROM items
# # => [{:column=>value, ...}, ...]
#
# If a block is given, it is passed to #each on the resulting dataset to
# iterate over the records returned by the query:
#
# DB.fetch('SELECT * FROM items'){|r| p r}
# # {:column=>value, ...}
# # ...
#
# +fetch+ can also perform parameterized queries for protection against SQL
# injection:
#
# ds = DB.fetch('SELECT * FROM items WHERE name = ?', "my name")
# ds.all
# # SELECT * FROM items WHERE name = 'my name'
#
# See caveats listed in Dataset#with_sql regarding datasets using custom
# SQL and the methods that can be called on them.
def fetch(sql, *args, &block)
ds = @default_dataset.with_sql(sql, *args)
ds.each(&block) if block
ds
end
# Returns a new dataset with the +from+ method invoked. If a block is given,
# it acts as a virtual row block
#
# DB.from(:items) # SELECT * FROM items
# DB.from{schema[:table]} # SELECT * FROM schema.table
def from(*args, &block)
if block
@default_dataset.from(*args, &block)
elsif args.length == 1 && (table = args[0]).is_a?(Symbol)
@default_dataset.send(:cached_dataset, :"_from_#{table}_ds"){@default_dataset.from(table)}
else
@default_dataset.from(*args)
end
end
# Returns a new dataset with the select method invoked.
#
# DB.select(1) # SELECT 1
# DB.select{server_version.function} # SELECT server_version()
# DB.select(:id).from(:items) # SELECT id FROM items
def select(*args, &block)
@default_dataset.select(*args, &block)
end
end
end
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