Rails for idiots #01 FlashCards for hash and CRUD

Rails for Idiots #01
hash and CRUD flashcards
Daisuke Ishii - CEO of www.jenio.co
Twitter@ishiid, email: dai@jenio.co
1

Let’s play like flashcards
2

Let’s learn Rails in easy way
Rails is so difficult for beginners like me.
I always feel there should be very easy documentation explaining Rails.
I will try to explain the basics of Rails in a easy way.
My idea is to create simple flash cards like when we memorize foreign languages.
Please use the following Q&A with your friend, asking each other.
3

What is hash in rails?
As well as array, hash is an object to manage multiple objects.
Example : hash1 = { “Andy” => 28, “Bob” => 30, “Keith” => 32, ……..}
Key: Andy, Bob, Keith…
Value: 28, 30, 32….
variable = {key, value} hash1 = { “Andy”, 28 }
variable[:key] = value hash1[“Andy”] = 28
4

Let’s take an example of database table called “tweets”
This is like an excel sheet.
id text user
1 I’m fine today. Andy
2 I’ve got married! Bob
3 I’ve got new job. Keith
5
*Table name is always lowercase & plural like “tweets”.

Q1: Please pick 3rd tweet and pass it to “t”.
6

Q1: Please pick 3rd tweet and pass it to “t”.
7
A: t = Tweet.find(3)
*Tweet needs to be singular and uppercase.

Q2: Now, display its id.
9
A: puts t[:id] => 3
or puts t.id => 3

Q3: Now, display its text.
A: puts t[:text] => I’ve got
new job.
or puts t.text => I’ve got new
job.
11

Q4: What is CRUD?
A: Create, Read, Update and
Delete. It is a basic
functions of computer
software.
14

Q5: Create new tweet saying ‘It is sunny’.
16

Q5: Create new tweet saying ‘It is sunny’.
A: t = Tweet.new
t.text = “It is sunny.”
t.save
*Tweet need to be singular and uppercase
17

Q6: Give me recipe of CREATE
18

Q6: Give me recipe of CREATE
A: t = TableName.new
t.key = value
t.save
19

Q7: Create Andy’s new tweet saying “See ya!”
20

Q7: Create Andy’s new tweet saying “See ya!”
A: t=Tweet.new( text: “See
ya!”, user: “Andy”)
t.save
*Tweet needs to be singular and uppercase
21

Q8: Give me recipe of CREATE hash
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Q8: Give me recipe of CREATE hash
A: t=TableName.new(hash)
t.save
*TableName needs to be singular and uppercase
23

Q9: Create Andy’s new tweet saying “See ya!” with
create method
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Q9: Create Andy’s new tweet saying “See ya!” with
create method
A: Tweet.create( text: “See
ya!”, user: “Andy”)
t.save
25

Q10: Give me recipe of CREATE hash with create
method
26

Q10: Give me recipe of CREATE hash with create
method
A: TableName.create(hash)
t.save
27

Q11: Find second tweet in database table
29

Q11: Find second tweet in database table
A: Tweet.find(2)
30

Q12: Find second, third, fourth tweets in database
table
31

Q12: Find second, third, fourth tweets in database
table
A: Tweet.find(3,4,5)
32

Q13: Find first tweet in database table
33

Q13: Find first tweet in database table
A: Tweet.first
34

Q14: Find last tweet in database table
35

Q14: Find last tweet in database table
A: Tweet.last
36

Q15: Find all tweets in database table
37

Q15: Find all tweets in database table
A: Tweet.all
38

Q16: Find total number of tweets
39

Q16: Find total number of tweets
A: Tweet.count
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Q17: Find all tweets ordered by users
41

Q17: Find all tweets ordered by users
A: Tweet.order(:user)
42

Q18: Find the first 10 tweets
43

Q18: Find the first 10 tweets
A: Tweet.limit(10)
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Q19: Find all tweets from user named “Bob”
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Q19: Find all tweets from user named “Bob”
A: Tweet.where(user:”Bob”)
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Q20: Find only tweets from user named “Bob”
ordered by text, only the first 10.
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Q20: Find only tweets from user named “Bob”
ordered by text, only the first 10.
A:Tweet.where(user:”Bob”).
order(:text).limit(10)
*This is called method chaining
48

Q21: Find only tweets from user named “Bob” just
the first one.
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Q21: Find only tweets from user named “Bob” just
the first one.
A:Tweet.where(user:”Bob”).
first
*This is called method chaining
50

Q22: Find 3rd tweet and pass it to t. Update its user
as “Andy”.
52

Q22: Find 3rd tweet and pass it to t. Update its user
as “Andy”.
A: t=Tweet.find(3)
t.user = “Andy”
t.save
*Tweet needs to be singular and uppercase 53

Q23: Give me a recipe of previous codes.
54

A: t=TableName.find(id)
t.key = value
t.save
*TableName needs to be singular and uppercase 55

Q24: Find 2nd tweet and pass it to t. Update its text
as “Hello” and user as “Andy”.
56

as “Hello” and user as “Andy”.
A: t=Tweet.find(2)
t.attributes = {
text: “Hello”
user: “Andy” }
t.save

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t.attributes = hash
t.save

as “Hello” and user as “Andy”. Use update method.
60

as “Hello” and user as “Andy”. Use update method.
A: t=Tweet.find(2)
t.update = {
text: “Hello”
user: “Andy” }
t.save

62

t = TableName.update(hash)
t.save

Q28: Find 3rd tweet and pass it to t. And delete it.
65

Q28: Find 3rd tweet and pass it to t. And delete it.
A: t=Tweet.find(3)
t.destroy
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67

t.destroy
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Q30: Find 3rd tweet and delete it in one line.
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Q30: Find 3rd tweet and delete it in one line.
A: t=Tweet.find(3).destroy
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71

A: t=TableName.find(id).
destroy
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Q32: Find all tweets and delete them in one line.
73

Q32: Find all tweets and delete them in one line.
A: t=Tweet.destroy_all
74

75

A: t=TableName.destroy_all
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Finish!!! Good Job!!! Let’s keep learning.
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Follow me@Twitter
& give me feedback!
https://twitter.com/ishiid

Rails for idiots #01 FlashCards for hash and CRUD

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Rails for idiots #01 FlashCards for hash and CRUD