Class | Sequel::SQL::VirtualRow |
In: |
lib/sequel/extensions/virtual_row_method_block.rb
lib/sequel/sql.rb |
Parent: | BasicObject |
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.