Default values on initialization

README.md

@@ -49,10 +49,10 @@ list = Kredis.list "mylist"
 list << "hello world!"               # => RPUSH mylist "hello world!"
 [ "hello world!" ] == list.elements  # => LRANGE mylist 0, -1
 
-integer_list = Kredis.list "myintegerlist", typed: :integer
-integer_list.append([ 1, 2, 3 ])        # => RPUSH myintegerlist "1" "2" "3"
-integer_list << 4                       # => RPUSH myintegerlist "4"
-[ 1, 2, 3, 4 ] == integer_list.elements # => LRANGE myintegerlist 0 -1
+integer_list = Kredis.list "myintegerlist", typed: :integer, default: [ 1, 2, 3 ] # => EXISTS? myintegerlist, RPUSH myintegerlist "1" "2" "3"
+integer_list.append([ 4, 5, 6 ])                                                  # => RPUSH myintegerlist "4" "5" "6"
+integer_list << 7                                                                 # => RPUSH myintegerlist "7"
+[ 1, 2, 3, 4, 5, 6, 7 ] == integer_list.elements                                  # => LRANGE myintegerlist 0 -1
 
 unique_list = Kredis.unique_list "myuniquelist"
 unique_list.append(%w[ 2 3 4 ])                # => LREM myuniquelist 0, "2" + LREM myuniquelist 0, "3" + LREM myuniquelist 0, "4"  + RPUSH myuniquelist "2", "3", "4"
@@ -163,15 +163,7 @@ sleep 0.6.seconds
 false == flag.marked?           #=> EXISTS myflag
 ```
 
-And using structures on a different than the default `shared` redis instance, relying on `config/redis/secondary.yml`:
-
-```ruby
-one_string = Kredis.string "mystring"
-two_string = Kredis.string "mystring", config: :secondary
-
-one_string.value = "just on shared"
-two_string.value != one_string.value
-```
+### Models
 
 You can use all these structures in models:
 
@@ -197,6 +189,29 @@ person.morning.value = "blue"                        # => SET people:5:morning
 true == person.morning.blue?                         # => GET people:5:morning
 ```
 
+### Default values
+
+You can set a default value for all types. For example:
+
+```ruby
+list = Kredis.list "favorite_colors", default: [ "red", "green", "blue" ]
+
+# or, in a model
+class Person < ApplicationRecord
+  kredis_string :name, default: "Unknown"
+  kredis_list :favorite_colors, default: [ "red", "green", "blue" ]
+end
+```
+
+There's a performance overhead to consider though. When you first read or write an attribute in a model, Kredis will
+check if the underlying Redis key exists, while watching for concurrent changes, and if it does not,
+write the specified default value.
+
+This means that using default values in a typical Rails app additional Redis calls (WATCH, EXISTS, UNWATCH) will be
+executed for each Kredis attribute with a default value read or written during a request.
+
+### Callbacks
+
 You can also define `after_change` callbacks that trigger on mutations:
 
 ```ruby
@@ -209,6 +224,18 @@ class Person < ApplicationRecord
 end
 ```
 
+### Multiple Redis servers
+
+And using structures on a different than the default `shared` redis instance, relying on `config/redis/secondary.yml`:
+
+```ruby
+one_string = Kredis.string "mystring"
+two_string = Kredis.string "mystring", config: :secondary
+
+one_string.value = "just on shared"
+two_string.value != one_string.value
+```
+
 ## Installation
 
 1. Run `./bin/bundle add kredis`

lib/kredis.rb

@@ -10,6 +10,7 @@
 require "kredis/log_subscriber"
 require "kredis/namespace"
 require "kredis/type_casting"
+require "kredis/default_values"
 require "kredis/types"
 require "kredis/attributes"
 

lib/kredis/attributes.rb

@@ -8,56 +8,56 @@ def kredis_proxy(name, key: nil, config: :shared, after_change: nil)
       kredis_connection_with __method__, name, key, config: config, after_change: after_change
     end
 
-    def kredis_string(name, key: nil, config: :shared, after_change: nil, expires_in: nil)
-      kredis_connection_with __method__, name, key, config: config, after_change: after_change, expires_in: expires_in
+    def kredis_string(name, key: nil, default: nil, config: :shared, after_change: nil, expires_in: nil)
+      kredis_connection_with __method__, name, key, default: default, config: config, after_change: after_change, expires_in: expires_in
     end
 
-    def kredis_integer(name, key: nil, config: :shared, after_change: nil, expires_in: nil)
-      kredis_connection_with __method__, name, key, config: config, after_change: after_change, expires_in: expires_in
+    def kredis_integer(name, key: nil, default: nil, config: :shared, after_change: nil, expires_in: nil)
+      kredis_connection_with __method__, name, key, default: default, config: config, after_change: after_change, expires_in: expires_in
     end
 
-    def kredis_decimal(name, key: nil, config: :shared, after_change: nil, expires_in: nil)
-      kredis_connection_with __method__, name, key, config: config, after_change: after_change, expires_in: expires_in
+    def kredis_decimal(name, key: nil, default: nil, config: :shared, after_change: nil, expires_in: nil)
+      kredis_connection_with __method__, name, key, default: default, config: config, after_change: after_change, expires_in: expires_in
     end
 
-    def kredis_datetime(name, key: nil, config: :shared, after_change: nil, expires_in: nil)
-      kredis_connection_with __method__, name, key, config: config, after_change: after_change, expires_in: expires_in
+    def kredis_datetime(name, key: nil, default: nil, config: :shared, after_change: nil, expires_in: nil)
+      kredis_connection_with __method__, name, key, default: default, config: config, after_change: after_change, expires_in: expires_in
     end
 
-    def kredis_flag(name, key: nil, config: :shared, after_change: nil, expires_in: nil)
-      kredis_connection_with __method__, name, key, config: config, after_change: after_change, expires_in: expires_in
+    def kredis_flag(name, key: nil, default: nil, config: :shared, after_change: nil, expires_in: nil)
+      kredis_connection_with __method__, name, key, default: default, config: config, after_change: after_change, expires_in: expires_in
 
       define_method("#{name}?") do
         send(name).marked?
       end
     end
 
-    def kredis_float(name, key: nil, config: :shared, after_change: nil, expires_in: nil)
-      kredis_connection_with __method__, name, key, config: config, after_change: after_change, expires_in: expires_in
+    def kredis_float(name, key: nil, default: nil, config: :shared, after_change: nil, expires_in: nil)
+      kredis_connection_with __method__, name, key, default: default, config: config, after_change: after_change, expires_in: expires_in
     end
 
     def kredis_enum(name, key: nil, values:, default:, config: :shared, after_change: nil)
       kredis_connection_with __method__, name, key, values: values, default: default, config: config, after_change: after_change
     end
 
-    def kredis_json(name, key: nil, config: :shared, after_change: nil, expires_in: nil)
-      kredis_connection_with __method__, name, key, config: config, after_change: after_change, expires_in: expires_in
+    def kredis_json(name, key: nil, default: nil, config: :shared, after_change: nil, expires_in: nil)
+      kredis_connection_with __method__, name, key, default: default, config: config, after_change: after_change, expires_in: expires_in
     end
 
-    def kredis_list(name, key: nil, typed: :string, config: :shared, after_change: nil)
-      kredis_connection_with __method__, name, key, typed: typed, config: config, after_change: after_change
+    def kredis_list(name, key: nil, default: nil, typed: :string, config: :shared, after_change: nil)
+      kredis_connection_with __method__, name, key, default: default, typed: typed, config: config, after_change: after_change
     end
 
-    def kredis_unique_list(name, limit: nil, key: nil, typed: :string, config: :shared, after_change: nil)
-      kredis_connection_with __method__, name, key, limit: limit, typed: typed, config: config, after_change: after_change
+    def kredis_unique_list(name, limit: nil, key: nil, default: nil, typed: :string, config: :shared, after_change: nil)
+      kredis_connection_with __method__, name, key, default: default, limit: limit, typed: typed, config: config, after_change: after_change
     end
 
-    def kredis_ordered_set(name, limit: nil, key: nil, typed: :string, config: :shared, after_change: nil)
-      kredis_connection_with __method__, name, key, limit: limit, typed: typed, config: config, after_change: after_change
+    def kredis_set(name, key: nil, default: nil, typed: :string, config: :shared, after_change: nil)
+      kredis_connection_with __method__, name, key, default: default, typed: typed, config: config, after_change: after_change
     end
 
-    def kredis_set(name, key: nil, typed: :string, config: :shared, after_change: nil)
-      kredis_connection_with __method__, name, key, typed: typed, config: config, after_change: after_change
+    def kredis_ordered_set(name, limit: nil, default: nil, key: nil, typed: :string, config: :shared, after_change: nil)
+      kredis_connection_with __method__, name, key, default: default, limit: limit, typed: typed, config: config, after_change: after_change
     end
 
     def kredis_slot(name, key: nil, config: :shared, after_change: nil)
@@ -68,16 +68,16 @@ def kredis_slots(name, available:, key: nil, config: :shared, after_change: nil)
       kredis_connection_with __method__, name, key, available: available, config: config, after_change: after_change
     end
 
-    def kredis_counter(name, key: nil, config: :shared, after_change: nil, expires_in: nil)
-      kredis_connection_with __method__, name, key, config: config, after_change: after_change, expires_in: expires_in
+    def kredis_counter(name, key: nil, default: nil, config: :shared, after_change: nil, expires_in: nil)
+      kredis_connection_with __method__, name, key, default: default, config: config, after_change: after_change, expires_in: expires_in
     end
 
-    def kredis_hash(name, key: nil, typed: :string, config: :shared, after_change: nil)
-      kredis_connection_with __method__, name, key, typed: typed, config: config, after_change: after_change
+    def kredis_hash(name, key: nil, default: nil, typed: :string, config: :shared, after_change: nil)
+      kredis_connection_with __method__, name, key, default: default, typed: typed, config: config, after_change: after_change
     end
 
-    def kredis_boolean(name, key: nil, config: :shared, after_change: nil, expires_in: nil)
-      kredis_connection_with __method__, name, key, config: config, after_change: after_change, expires_in: expires_in
+    def kredis_boolean(name, key: nil, default: nil, config: :shared, after_change: nil, expires_in: nil)
+      kredis_connection_with __method__, name, key, default: default, config: config, after_change: after_change, expires_in: expires_in
     end
 
     private
@@ -90,6 +90,7 @@ def kredis_connection_with(method, name, key, **options)
           if instance_variable_defined?(ivar_symbol)
             instance_variable_get(ivar_symbol)
           else
+            options[:default] = kredis_default_evaluated(options[:default]) if options[:default]
             new_type = Kredis.send(type, kredis_key_evaluated(key) || kredis_key_for_attribute(name), **options)
             instance_variable_set ivar_symbol,
               after_change ? enrich_after_change_with_record_access(new_type, after_change) : new_type
@@ -121,4 +122,12 @@ def enrich_after_change_with_record_access(type, original_after_change)
       when Symbol then Kredis::Types::CallbacksProxy.new(type, ->(_) { send(original_after_change) })
       end
     end
+
+    def kredis_default_evaluated(default)
+      case default
+      when Proc   then Proc.new { default.call(self) }
+      when Symbol then send(default)
+      else default
+      end
+    end
 end

lib/kredis/default_values.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+module Kredis::DefaultValues
+  extend ActiveSupport::Concern
+
+  prepended do
+    attr_writer :default
+
+    proxying :watch, :unwatch, :exists?
+
+    def default
+      case @default
+      when Proc   then @default.call
+      when Symbol then send(@default)
+      else @default
+      end
+    end
+
+    private
+      def set_default
+        raise NotImplementedError, "Kredis type #{self.class} needs to define #set_default"
+      end
+  end
+
+  def initialize(...)
+    super
+
+    if default
+      watch do
+        set_default unless exists?
+
+        unwatch
+      end
+    end
+  end
+end

lib/kredis/types.rb

@@ -41,40 +41,40 @@ def json(key, default: nil, config: :shared, after_change: nil, expires_in: nil)
   end
 
 
-  def counter(key, expires_in: nil, config: :shared, after_change: nil)
-    type_from(Counter, config, key, after_change: after_change, expires_in: expires_in)
+  def counter(key, expires_in: nil, default: nil, config: :shared, after_change: nil)
+    type_from(Counter, config, key, after_change: after_change, default: default, expires_in: expires_in)
   end
 
   def cycle(key, values:, expires_in: nil, config: :shared, after_change: nil)
     type_from(Cycle, config, key, after_change: after_change, values: values, expires_in: expires_in)
   end
 
-  def flag(key, config: :shared, after_change: nil, expires_in: nil)
-    type_from(Flag, config, key, after_change: after_change, expires_in: expires_in)
+  def flag(key, default: nil, config: :shared, after_change: nil, expires_in: nil)
+    type_from(Flag, config, key, after_change: after_change, default: default, expires_in: expires_in)
   end
 
   def enum(key, values:, default:, config: :shared, after_change: nil)
     type_from(Enum, config, key, after_change: after_change, values: values, default: default)
   end
 
-  def hash(key, typed: :string, config: :shared, after_change: nil)
-    type_from(Hash, config, key, after_change: after_change, typed: typed)
+  def hash(key, typed: :string, default: nil, config: :shared, after_change: nil)
+    type_from(Hash, config, key, after_change: after_change, default: default, typed: typed)
   end
 
-  def list(key, typed: :string, config: :shared, after_change: nil)
-    type_from(List, config, key, after_change: after_change, typed: typed)
+  def list(key, default: nil, typed: :string, config: :shared, after_change: nil)
+    type_from(List, config, key, after_change: after_change, default: default, typed: typed)
   end
 
-  def unique_list(key, typed: :string, limit: nil, config: :shared, after_change: nil)
-    type_from(UniqueList, config, key, after_change: after_change, typed: typed, limit: limit)
+  def unique_list(key, default: nil, typed: :string, limit: nil, config: :shared, after_change: nil)
+    type_from(UniqueList, config, key, after_change: after_change, default: default, typed: typed, limit: limit)
   end
 
-  def set(key, typed: :string, config: :shared, after_change: nil)
-    type_from(Set, config, key, after_change: after_change, typed: typed)
+  def set(key, default: nil, typed: :string, config: :shared, after_change: nil)
+    type_from(Set, config, key, after_change: after_change, default: default, typed: typed)
   end
 
-  def ordered_set(key, typed: :string, limit: nil, config: :shared, after_change: nil)
-    type_from(OrderedSet, config, key, after_change: after_change, typed: typed, limit: limit)
+  def ordered_set(key, default: nil, typed: :string, limit: nil, config: :shared, after_change: nil)
+    type_from(OrderedSet, config, key, after_change: after_change, default: default, typed: typed, limit: limit)
   end
 
   def slot(key, config: :shared, after_change: nil)

lib/kredis/types/counter.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 class Kredis::Types::Counter < Kredis::Types::Proxying
+  prepend Kredis::DefaultValues
+
   proxying :multi, :set, :incrby, :decrby, :get, :del, :exists?
 
   attr_accessor :expires_in
@@ -26,4 +28,9 @@ def value
   def reset
     del
   end
+
+  private
+    def set_default
+      increment by: default
+    end
 end

lib/kredis/types/enum.rb

@@ -3,9 +3,13 @@
 require "active_support/core_ext/object/inclusion"
 
 class Kredis::Types::Enum < Kredis::Types::Proxying
-  proxying :set, :get, :del, :exists?
+  prepend Kredis::DefaultValues
 
-  attr_accessor :values, :default
+  InvalidDefault = Class.new(StandardError)
+
+  proxying :set, :get, :del, :exists?, :multi
+
+  attr_accessor :values
 
   def initialize(...)
     super
@@ -19,11 +23,14 @@ def value=(value)
   end
 
   def value
-    get || default
+    get
   end
 
   def reset
-    del
+    multi do
+      del
+      set_default
+    end
   end
 
   private
@@ -33,4 +40,12 @@ def define_predicates_for_values
         define_singleton_method("#{defined_value}!") { self.value = defined_value }
       end
     end
+
+    def set_default
+      if default.in?(values) || default.nil?
+        set default
+      else
+        raise InvalidDefault, "Default value #{default.inspect} for #{key} is not a valid option (Valid values: #{values.join(", ")})"
+      end
+    end
 end

lib/kredis/types/flag.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 class Kredis::Types::Flag < Kredis::Types::Proxying
+  prepend Kredis::DefaultValues
+
   proxying :set, :exists?, :del
 
   attr_accessor :expires_in
@@ -16,4 +18,9 @@ def marked?
   def remove
     del
   end
+
+  private
+    def set_default
+      mark if default
+    end
 end