Class: Sequel::SQL::VirtualRow

Inherits:

BasicObject

Defined in:

lib/sequel/sql.rb

Overview

The purpose of the VirtualRow class is to allow the easy creation of SQL identifiers and functions without relying on methods defined on Symbol. This is useful if another library defines the methods defined by Sequel, if you are running on ruby 1.9, or if you are not using the core extensions.

An instance of this class is yielded to the block supplied to Dataset#filter, Dataset#order, and Dataset#select (and the other methods that accept a block and pass it to one of those methods). If the block doesn’t take an argument, the block is instance_evaled in the context of a new instance of this class.

VirtualRow uses method_missing to return either an Identifier, QualifiedIdentifier, Function, or WindowFunction, depending on how it is called.

If a block is not given, creates one of the following objects:

Function

Returned if any arguments are supplied, using the method name as the function name, and the arguments as the function arguments.

QualifiedIdentifier

Returned if the method name contains __, with the table being the part before __, and the column being the part after.

Identifier

Returned otherwise, using the method name.

If a block is given, it returns either a Function or WindowFunction, depending on the first argument to the method. Note that the block is currently not called by the code, though this may change in a future version. If the first argument is:

no arguments given

creates a Function with no arguments.

:*

creates a Function with a literal wildcard argument (*), mostly useful for COUNT.

:distinct

creates a Function that prepends DISTINCT to the rest of the arguments, mostly useful for aggregate functions.

:over

creates a WindowFunction. If a second argument is provided, it should be a hash of options which are passed to Window (with possible keys :window, :partition, :order, and :frame). The arguments to the function itself should be specified as :*=>true for a wildcard, or via the :args option.

Examples:

ds = DB[:t]
# Argument yielded to block
ds.filter{|r| r.name < 2} # SELECT * FROM t WHERE (name < 2)
# Block without argument (instance_eval)
ds.filter{name < 2} # SELECT * FROM t WHERE (name < 2)
# Qualified identifiers
ds.filter{table__column + 1 < 2} # SELECT * FROM t WHERE ((table.column + 1) < 2)
# Functions
ds.filter{is_active(1, 'arg2')} # SELECT * FROM t WHERE is_active(1, 'arg2')
ds.select{version{}} # SELECT version() FROM t
ds.select{count(:*){}} # SELECT count(*) FROM t
ds.select{count(:distinct, col1){}} # SELECT count(DISTINCT col1) FROM t
# Window Functions
ds.select{rank(:over){}} # SELECT rank() OVER () FROM t
ds.select{count(:over, :*=>true){}} # SELECT count(*) OVER () FROM t
ds.select{sum(:over, :args=>col1, :partition=>col2, :order=>col3){}} # SELECT sum(col1) OVER (PARTITION BY col2 ORDER BY col3) FROM t

For a more detailed explanation, see the Virtual Rows guide.

Constant Summary

WILDCARD =

LiteralString.new('*').freeze

QUESTION_MARK =

LiteralString.new('?').freeze

COMMA_SEPARATOR =

LiteralString.new(', ').freeze

DOUBLE_UNDERSCORE =

'__'.freeze

Constants inherited from BasicObject

BasicObject::KEEP_METHODS

Instance Method Summary

• #method_missing(m, *args, &block) ⇒ Object

  Return an Identifier, QualifiedIdentifier, Function, or WindowFunction, depending on arguments and whether a block is provided.

Methods inherited from BasicObject

const_missing, remove_methods!

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

#method_missing(m, *args, &block) ⇒ Object

Return an Identifier, QualifiedIdentifier, Function, or WindowFunction, depending on arguments and whether a block is provided. Does not currently call the block. See the class level documentation.

# File 'lib/sequel/sql.rb', line 1104

def method_missing(m, *args, &block)
  if block
    if args.empty?
      Function.new(m)
    else
      case arg = args.shift
      when :*
        Function.new(m, WILDCARD)
      when :distinct
        Function.new(m, PlaceholderLiteralString.new("DISTINCT #{args.map{QUESTION_MARK}.join(COMMA_SEPARATOR)}", args))
      when :over
        opts = args.shift || {}
        fun_args = ::Kernel.Array(opts[:*] ? WILDCARD : opts[:args])
        WindowFunction.new(Function.new(m, *fun_args), Window.new(opts))
      else
        raise Error, 'unsupported VirtualRow method argument used with block'
      end
    end
  elsif args.empty?
    table, column = m.to_s.split(DOUBLE_UNDERSCORE, 2)
    column ? QualifiedIdentifier.new(table, column) : Identifier.new(m)
  else
    Function.new(m, *args)
  end
end