Add more info

docs/design/README.md

@@ -0,0 +1,7 @@
+# Software design
+
+Welcome to software design page. Please open menu and enjoy.
+
+- [See the main script]()
+- [Single responsibility for object]()
+- [System should do one thing and to it well]()

docs/ruby/045.md

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+# How to declare unary operator
+
+In Ruby a class can have methods like `+`, `-`, etc.
+
+```ruby
+class MyString
+  def initialize(str)
+    @str = str
+  end
+
+  def +(string)
+    self.class.new("#{@str} #{string}")
+  end
+
+  def inspect
+    to_s
+  end
+
+  def to_s
+    "#{@str}"
+  end
+end
+
+a = MyString.new('My String.')
+
+puts a + 'Add some string'
+# "My String. Add some string"
+```
+
+We also can declare an unary operator like `!object`, `+object`, `-object`, etc.
+
+```ruby
+class MyString
+  def +@
+    # add a space before
+    self.class.new(" #{@str}")
+  end
+
+  def -@
+    # delete first character
+    self.class.new(@str[1..-1])
+  end
+end
+
+puts +++a + ' Wow!'
+# "   My String.  Wow!"
+puts ---a
+# "String."
+```
+
+Some declare unary operators can be declared without `@`
+
+```ruby
+class MyString
+  def !
+    # check string length
+    @str.size > 0
+  end
+end
+
+puts !MyString.new('My String.')
+# true
+puts !MyString.new('')
+# false
+```
+
+List of methods:
+
+- `**`
+- `!` `~` `+` `+@` `–` `-@`
+- `*` `/` `%`
+- `>>` `<<`
+- `&`
+- `^` `|`
+- `<=` `<>` `>=`
+- `<=>` `==` `===!` `=` `=` `~!` `~`

docs/ruby/README.md

@@ -48,6 +48,7 @@ Welcome to Ruby page. Please open menu and enjoy.
 - [String interpolation and to_s method](ruby/042.md)
 - [Decorators for methods](ruby/043.md)
 - [Private and protected](ruby/044.md)
+- [How to declare unary operator](ruby/045.md)
 
 ## Links
 

docs/ruby_on_rails/014.md

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+# find vs find_by
+
+`find` - it raises `ActiveRecord::RecordNotFound`` exception
+
+`find_by` - it can return `nil`
+
+`find_by!` - it raises `ActiveRecord::RecordNotFound`` exception

docs/ruby_on_rails/015.md

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+# preload vs includes
+
+### Joins
+
+```ruby
+User.joins(:posts).where(posts: { active: true })
+```
+
+* uses inner join
+* does not load associated records in memory.
+* executes single query
+* it does not solve n+1 problem
+
+### Preload
+
+```ruby
+User.preload(:posts)
+```
+
+* does not perform join
+* load associated data in memory.
+* executes multiple queries
+* it solves n+1 problem
+
+### Includes
+
+```ruby
+User.includes(:posts)
+
+User.includes(:posts).references(:posts)
+```
+
+* perform left outer join and store associated data in the memory.
+* Sometimes generate one query and sometimes generates 2 queries
+* If you want to force to use a single query you can add references
+* it solves n+1 problem
+
+### Eager load
+
+```ruby
+User.eager_load(:posts).where("posts.visible = ?", true)
+```
+
+* Load associated data in memory
+* Performs LEFT OUTER join
+* Forces to use a single query
+* Some times takes more time than two queries
+* it solves n+1 problem
+
+[source](https://techrello.com/ruby-on-rails/joins-vs-preload-vs-includes-vs-eager-load-in-rails)

docs/ruby_on_rails/README.md

@@ -17,6 +17,8 @@ Welcome to Ruby on Rails page. Please open menu and enjoy.
 - [How to share data between class and instance](ruby_on_rails/011.md)
 - [Security tools](ruby_on_rails/012.md)
 - [Railsdiff](ruby_on_rails/013.md)
+- [find vs find_by](ruby_on_rails/014.md)
+- [preload vs includes](ruby_on_rails/015.md)
 
 ## Links
 

docs/terminal/README.md

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+# Terminal
+
+Welcome to terminal page. Please open menu and enjoy.