Method: Sequel::SQL::Builders#expr

Defined in:
lib/sequel/sql.rb

#expr(arg = (no_arg=true), &block) ⇒ Object

Wraps the given object in an appropriate Sequel wrapper. If the given object is already a Sequel object, return it directly. For condition specifiers (hashes and arrays of two pairs), true, and false, return a boolean expressions. For numeric objects, return a numeric expression. For strings, return a string expression. For procs or when the method is passed a block, evaluate it as a virtual row and wrap it appropriately. In all other cases, use a generic wrapper.

This method allows you to construct SQL expressions that are difficult to construct via other methods. For example:

Sequel.expr(1) - :a # SQL: (1 - a)



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# File 'lib/sequel/sql.rb', line 442

def expr(arg=(no_arg=true), &block)
  if block_given?
    if no_arg
      return expr(block)
    else
      raise Error, 'cannot provide both an argument and a block to Sequel.expr'
    end
  elsif no_arg
    raise Error, 'must provide either an argument or a block to Sequel.expr'
  end

  case arg
  when Symbol
    t, c, a = Sequel.split_symbol(arg)

    arg = if t
      SQL::QualifiedIdentifier.new(t, c)
    else
      SQL::Identifier.new(c)
    end

    if a
      arg = SQL::AliasedExpression.new(arg, a)
    end

    arg
  when SQL::Expression, LiteralString, SQL::Blob
    arg
  when Hash
    SQL::BooleanExpression.from_value_pairs(arg, :AND)
  when Array
    if condition_specifier?(arg)
      SQL::BooleanExpression.from_value_pairs(arg, :AND)
    else
      SQL::Wrapper.new(arg)
    end
  when Numeric
    SQL::NumericExpression.new(:NOOP, arg)
  when String
    SQL::StringExpression.new(:NOOP, arg)
  when TrueClass, FalseClass
    SQL::BooleanExpression.new(:NOOP, arg)
  when Proc
    expr(virtual_row(&arg))
  else
    SQL::Wrapper.new(arg)
  end
end