更新Rails表中的记录

Question

I have a table A(:name, :flag) and want to update the flag column of a record in the table if a certain condition evaluates to true.

if A.find(300).flag == false
 //Will this work -> A.find(300).flag = true

What should I write in that line?

Answer 1

if A.find(300).flag == false
 //Will this work -> A.find(300).flag = true

change to

A.find(300).update(flag: true) if A.find(300).flag == false

You can add method to a.rb

def self.update_if_false id
  find(id).update(flasg: true) if A.find(id).flag == false
end

Then you can use it as A.update_if_false(300)

Answer 2

This will decrease database call if flag is true:

Rails 4:

obj = A.find(300)
obj.update(flag: true) unless obj.flag

Rails 3.2:

obj = A.find(300)
obj.update_attributes(flag: true) unless obj.flag

Note: update method made public and aliased with update_attributes in active record 4.

Answer 3

yes..it will work...i tried in ruby2.0 console.. Assuming you have all the attributes present....

2.0.0-p481 :026 >  Image.find(30).title = true
Image Load (7.8ms)  SELECT "images".* FROM "images" WHERE "images"."id" = $1 LIMIT 1  [["id", 30]]
 => true 

you can go ahead and add your update statement ..if true else false.

if A.find(300).flag == false
  ##do something
else
  ##do other thing
end