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, in a way that leads to more compact code.

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, Function depending on how it is called.

Function

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

Identifier

Returned otherwise, using the method name.

If splitting symbols has been enabled (not the default), then method calls without arguments will return QualifiedIdentifier instances if the method call includes a double underscore.

Examples:

ds = DB[:t]

# Argument yielded to block
ds.where{|r| r.name < 2} # SELECT * FROM t WHERE (name < 2)

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

# Functions
ds.where{is_active(1, 'arg2')} # SELECT * FROM t WHERE is_active(1, 'arg2')
ds.select{version.function} # SELECT version() FROM t
ds.select{count.function.*} # SELECT count(*) FROM t
ds.select{count(col1).distinct} # SELECT count(DISTINCT col1) 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)

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

Instance Method Summary collapse

Methods included from OperatorBuilders

#**, #~

Methods inherited from BasicObject

const_missing

Constructor Details

#initialize ⇒ VirtualRow

Returns a new instance of VirtualRow.



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# File 'lib/sequel/sql.rb', line 1913

def initialize
  freeze
end