```ruby
ACTIVE RECORD LECTURE -KEVIN (092817)

Active record playground

ruby <-- active record --> SQL

why ruby?
- framework rails ( what we use to write a website )
- automation
why SQL? database
 - only allows you to store data; no automation


######
                #SQL command
# -create : insert into
# -read   : SELECT
# -update : UPDATE
# -delete (data): DELETE FROM


#which name do you connect to? based on the class name?

# class name person, then table is people



# rb(main):001:0> load 'playground.rb'
# => true


CREATE and SAVE NEW student/ object

#this just creates objects but does not include to the database.

# irb(main):004:0> a = Student.new
# => #<Student id: nil, name: nil, email: nil, age: nil, cre
# ated_at: nil, updated_at: nil>



# rb(main):005:0> b = Student.new(name: 'kevin', email: 'ke
# vin@example.com')
# => #<Student id: nil, name: "kevin", email: "kevin@example
# .com", age: nil, created_at: nil, updated_at: nil>


# how to put this into the database?
# rb(main):006:0> b.save
# => true


#tudent@728c41844461:~$ sqlite3 students.sqlite3
#sqlite> select * from students;
#kevin has been entered






############################################

# irb
# loairb(main):001:0> load 'playground.rb'


When saved, then you have automatically assigned id (incremented id)

# rb(main):002:0> boy = Student.new(name: 'boy', email: 'boy@boy
# .com')
 => <Student id: nil, name: "boy", email: "boy@boy.com", age: n
# il, created_at: nil, updated_at: nil>
# irb(main):003:0> boy.save
# => true
# irb(main):004:0> boy
 => <Student id: 22, name: "boy", email: "boy@boy.com", age: ni
# l, created_at: "2017-09-28 07:35:07", updated_at: "2017-09-28 0


UPDATE changing attribute (update)
 boy.update(name: 'girl', email: "notboy@boy.co
m)



find 'kevin' first
#assume that I know is 21 my id

 Student.find(21)
# => #<Student id: 21, name: "kevin", email: "kevin@example.com",
#  age: nil, created_at: "2017-09-28 07:27:07", updated_at: "2017
# -09-28 07:27:07">

Kevin = Student.find(21)
# #<Student id: 21, name: "kevin", email: "kevin@example.com",
#  age: nil, created_at: "2017-09-28 07:27:07", updated_at: "2017
# -09-28 07:27:07">


 Student.find_by(email: 'kevin@example.com')
# => #<Student id: 21, name: "kevin", email: "kevin@example.com",
#  age: nil, created_at: "2017-09-28 07:27:07", updated_at: "2017
# -09-28 07:27:07">



# ActiveRecord::Base  library?

SAVE
#  a.name = "kevinsia"
# => "kevinsia"
# irb(main):017:0> a.save
# => true


Student.all & Last Student
# a  = Student.all
#a[-1] => last student
# last_student = Student.last

#last_student.name


Update
# y = Student.find(12)
# y.update(email: 'haha@hah.com')



WHERE: find same name more than one (i.e. kevinsia)

# Student.where(name: 'kevinsia')
# => #<ActiveRecord::Relation [#<Student id: 21, name: "kevinsia"
# , email: "kevin@hansome.com", age: nil, created_at: "2017-09-28
#  07:27:07", updated_at: "2017-09-28 07:45:55">]>


.count : count the number
# Student.where(name: 'kevinsia').count
# => 2


age less than?
Student.where('age <?', 18)
#Student.where('age <?', 18).count => 5


name starts with K?
Student.where('name LIKE ?', 'k%')
# => #<ActiveRecord::Relation [#<Student id: 21, name: "kevinsia"
# , email: "kevin@hansome.com", age: nil, created_at: "2017-09-28
#  07:27:07", updated_at: "2017-09-28 07:45:55">, #<Student id: 2
# 4, name: "kevinsia", email: "different@g.com", age: nil, create
# d_at: "2017-09-28 08:00:21", updated_at: "2017-09-28 08:00:21">
# ]>

#BE CAREFUL! SQL injection = avoid name LIKE k%


WHERE & Two conditions
Student.where('name LIKE ? AND age <?', 'M%',18)
# => #<ActiveRecord::Relation [#<Student id: 11, name: "Miss Toy
# Hickle", email: "tracy.kunde@herman.info", age: 17, created_at:
#  "2017-01-25 08:44:17", updated_at: "2017-01-25 08:44:17">]>
# irb(main):027:0>



a.destroy or Student.destry(24)
#a.dstory
# => #<Student id: 21, name: "kevinsia", email: "kevin@hansome.co
# m", age: nil, created_at: "2017-09-28 07:27:07", updated_at: "2
# 017-09-28 07:45:55">

# Student.destroy(24)
# => #<Student id: 24, name: "kevinsia", email: "different@g.com"
# , age: nil, created_at: "2017-09-28 08:00:21", updated_at: "201
# 7-09-28 08:00:21">



behaves like array! :example1
Student.where("age <?", 18).each do |student|
      puts student.name
 end

 #=> Sofia Gleichner IV Rod Harvey Miss Toy Hickle Hardy Jerde Beau Sanford



behaves like array! :example2
Student.where("age <?", 18).each do |student|
    puts "#{student.id}:#{student.name},#{student.
email}"end


# 7:Sofia Gleichner IV,evalyn@feeney.org
# 8:Rod Harvey,janea.lindgren@flatleybrown.com
# 11:Miss Toy Hickle,tracy.kunde@herman.info
# 13:Hardy Jerde,raquel_schamberger@hudsondickinson.com
# 15:Beau Sanford,thelma_altenwerth@swaniawski.info








####################################
# Write your test code here

# 1. Create a new student using new and save
      b = Student.new
      b.save
# 2. Create a new student using create
    Student.create(name: 'kevin')

# 3. Select all students
     Student.all
# pay attention to the object that is returned to you, is it a Student object or Active Record relation object?
   #Relations object?
   Active Record relation object is a collection of student object; generate from class.all, class. where
   actual object you can create, update, save.

# Why can't you do Student.name or Student.email?
 you cant put .(dot) on Class to get name or email. you can do it on one individual student object

# pay attention to the object that is returned to you, is it a Student object or Active Record relation object?
    #Student.all returned <ActiveRecord::Relation [


# 4. Select the first student
=> #<Student id: 1, name: "Grayson Bednar", email: "emmy@schneider.net", age:
 #20, created_at: "2017-01-25 08:44:05", updated_at: "2017-01-25 08:44:05">


# 5. Select the last student
#<Student id: 20, name: "Miss Lori Johns", email: "maximo@batz.net", age:
#20, created_at: "2017-01-25 08:44:21", updated_at: "2017-01-25 08:44:21">
# pay attention to the object that is returned to you, is it a Student object or Active Record relation object?
   #STUDENT object



# 6. Use each to iterate through the #<ActiveRecord::Relation> object to display the name of each student
Student.where("age<?",18) each do |student| puts student.name end


# 7. Find student by the name Dr. Lois Pfeffer using where.
# pay attention to the object that is returned to you, is it the Student object or Active Record relation object?
Student.where('name LIKE ?', "Dr%")
# What will the following return to you? (remember to comment out the code!)
# p student.id
# p student.name
# p student.email
# p student.age


# 8. Find student by name using find_by
# pay attention to the object that is returned to you, is it the Student object or Active Record relation object?

# What will the following return to you?
# p student.id
# p student.name
# p student.email
# p student.age

   => there is nothing stored in student. you create new object and then

# Do research on the difference between "where" and "find_by".

# 9. Find the student with id = 7 using find and find_by
# pay attention to the object that is returned to you, is it the User object or Active Record relation object?
Student.find(7)
Student.find_by(id: 7)


# 10. Update information for student with id = 5 using student.email and save. Change the student's email to elsie@example.com
student = Student.find(5)
student.update(email: "elase@example.com")
# 11. Now use update to update this student's age to 21.

# 12. Delete student with id 21 using destroy

# 13. Delete student with id 22 using destroy




```