Class: Sequel::SQL::VirtualRow

Inherits:: BasicObject

Includes:: OperatorBuilders

Defined in:: lib/sequel/sql.rb,
lib/sequel/extensions/virtual_row_method_block.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#where, 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_execed in the context of an instance of this class.

VirtualRow uses method_missing to return either an Identifier, QualifiedIdentifier, or Function 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 a Function. 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 Function with a window. If a second argument is provided, it should be a hash of options which are used to create the 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.where{|r| r.name < 2} # SELECT * FROM t WHERE (name < 2)

# Block without argument (instance_eval)
ds.where{name < 2} # SELECT * FROM t WHERE (name < 2)

# Qualified identifiers
ds.where{table__column + 1 < 2} # SELECT * FROM t WHERE ((table.column + 1) < 2)

# Functions
ds.where{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

# Math Operators
ds.select{|o| o.+(1, :a).as(:b)} # SELECT (1 + a) AS b FROM t
ds.select{|o| o.-(2, :a).as(:b)} # SELECT (2 - a) AS b FROM t
ds.select{|o| o.*(3, :a).as(:b)} # SELECT (3 * a) AS b FROM t
ds.select{|o| o./(4, :a).as(:b)} # SELECT (4 / a) AS b FROM t

# Boolean Operators
ds.where{|o| o.&({:a=>1}, :b)}    # SELECT * FROM t WHERE ((a = 1) AND b)
ds.where{|o| o.|({:a=>1}, :b)}    # SELECT * FROM t WHERE ((a = 1) OR b)
ds.where{|o| o.~({:a=>1})}        # SELECT * FROM t WHERE (a != 1)
ds.where{|o| o.~({:a=>1, :b=>2})} # SELECT * FROM t WHERE ((a != 1) OR (b != 2))

# Inequality Operators
ds.where{|o| o.>(1, :a)}  # SELECT * FROM t WHERE (1 > a)
ds.where{|o| o.<(2, :a)}  # SELECT * FROM t WHERE (2 < a)
ds.where{|o| o.>=(3, :a)} # SELECT * FROM t WHERE (3 >= a)
ds.where{|o| o.<=(4, :a)} # SELECT * FROM t WHERE (4 <= a)

# Literal Strings
ds.where{{a=>`some SQL`}} # SELECT * FROM t WHERE (a = some SQL)

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

Constant Summary collapse

QUESTION_MARK =

LiteralString.new('?').freeze

DOUBLE_UNDERSCORE =

'__'.freeze

Constants inherited from BasicObject

BasicObject::KEEP_METHODS

Instance Method Summary collapse

#`(s) ⇒ Object

Return a literal string created with the given string.
#initialize ⇒ VirtualRow constructor

A new instance of VirtualRow.

Methods included from OperatorBuilders

#**, #~

Methods inherited from BasicObject

const_missing, remove_methods!

Constructor Details

#initialize ⇒ `VirtualRow`

Returns a new instance of VirtualRow.



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# File 'lib/sequel/sql.rb', line 1932

def initialize
  freeze
end

Instance Method Details

#`(s) ⇒ `Object`

Return a literal string created with the given string.

# File 'lib/sequel/sql.rb', line 1937

def `(s)
  Sequel::Deprecation.deprecate("Using Sequel#VirtualRow#` to create a literal SQL fragment", "Use Sequel.lit instead")
  Sequel::LiteralString.new(s)
end