class Cascading::ExprStub

Attributes

expression[RW]

input_expression[RW]

types[RW]

Public Instance Methods

compile() click to toggle source

Scan, parse, and compile expression, then return this ExprStub upon success. Throws an CascadingException upon failure.

# File lib/cascading/expr_stub.rb, line 61
def compile
  evaluator
  self
end

eval(actual_args) click to toggle source

Evaluates this ExprStub given a hash mapping argument names to argument values. Names may be strings or symbols. Throws an CascadingException upon failure.

# File lib/cascading/expr_stub.rb, line 69
def eval(actual_args)
  actual_args = actual_args.inject({}) do |string_keys, (arg, value)|
    string_keys[arg.to_s] = specific_to_java(value, @types[arg.to_s])
    string_keys
  end
  args, values = split_hash(actual_args)
  unused = validate_fields(args)
  return self.eval(actual_args.reject{ |arg, value| unused.include?(arg) }) unless unused.empty?
  evaluate(values)
end

names_and_types() click to toggle source

Extract Java names and types from @types hash. Cascading constructors often require two separate Java Arrays in this fashion.

# File lib/cascading/expr_stub.rb, line 26
def names_and_types
  names, types = split_hash(@types)
  [names.to_java(java.lang.String), types.to_java(java.lang.Class)]
end

to_s() click to toggle source

Prints the original input expression.

# File lib/cascading/expr_stub.rb, line 32
def to_s
  @input_expression
end

validate(actual_args = {}) click to toggle source

Evaluates this ExprStub with default values for each actual argument. Values may be overridden with the optional actual_args argument, which accepts a hash like #eval. Throws an CascadingException upon failure.

# File lib/cascading/expr_stub.rb, line 84
def validate(actual_args = {})
  self.eval(test_values.merge(actual_args))
end

validate_fields(fields) click to toggle source

Throws an exception if any arguments required by this ExprStub are missing from fields. Returns those fields which are unused. Throws an ExprArgException upon failure.

# File lib/cascading/expr_stub.rb, line 98
def validate_fields(fields)
  names = @types.keys.sort
  missing = names - fields
  raise ExprArgException.new("Expression '#{@expression}' is missing these fields: #{missing.inspect}\nRequires: #{names.inspect}, found: #{fields.inspect}") unless missing.empty?
  fields - names
end

validate_scope(scope) click to toggle source

Given a scope, validates that the fields required by this ExprStub are available in the values fields of the scope. Returns those values fields which are unused in the expression.

# File lib/cascading/expr_stub.rb, line 91
def validate_scope(scope)
  validate_fields(scope.values_fields.to_a)
end

Public Class Methods

expr(expression, options = {}) click to toggle source

Convenience constructor for an ExprStub that optionally performs validation. Takes a string to use as a Janino expression and an optional options hash.

The named options are:

validate: A boolean indicating whether expression validation using default actual argument values should be performed. Defaults to true.
validate_with: A hash mapping field names (or symbols) to the value that should be used for validation. Strings default to nil, so if you have previously filtered nulls you might use a marker value like ‘nulls_filtered’. Defaults to {}.

Example:

insert 'x_eq_y' => expr('x:string.equals(y:string)', :validate_with => { :x => 'nulls_filtered' })

# File lib/cascading/expr_stub.rb, line 51
def self.expr(expression, options = {})
  options = { :validate => true, :validate_with => {} }.merge(options)
  expr_stub = expression.kind_of?(ExprStub) ? expression : ExprStub.new(expression).compile
  expr_stub.validate(options[:validate_with]) if options[:validate]
  puts "Expression validation is disabled for '#{expression}'" unless options[:validate]
  expr_stub
end

new(expression) click to toggle source

ExprStub requires a Janino expression decorated with field types. For example:

expr('"Found: " + (x:int + y:int) + " " + z:string')

Type names are defined in Cascading::JAVA_TYPE_MAP.

# File lib/cascading/expr_stub.rb, line 9
def initialize(expression)
  @input_expression = expression
  @expression = expression.dup
  @types = {}

  # Simple regexp based parser for types
  JAVA_TYPE_MAP.each do |sym, klass|
    @expression.gsub!(/[A-Za-z0-9_]+:#{sym.to_s}/) do |match|
      name = match.split(/:/).first.gsub(/\s+/, "")
      @types[name] = klass
      match.gsub(/:#{sym.to_s}/, "")
    end
  end
end