Creating a new object from another object's attributes in rails

Question

Before introducing strong params it was working fine. So, on creating a new object using new and passing attributes, id was being set as nil.

But now, when I am creating a new object, obj2 from existing object, obj1's attributes,

id(a primary key) of obj1 is also being copied to obj2.

Like,

obj2 = Post.new obj1.attributes

So, problem arises when I try to save it,

obj2.save

with ActiveRecord::RecordNotUnique error. As both object have the same id.

I have several models with the same use case, so if I use dup or except, I'll have to add the same in each case.

Possible duplicate of What is the easiest way to duplicate an activerecord record? — scoudert
– scoudert, Commented Feb 6, 2018 at 17:31

bitsapien · Accepted Answer · 2018-02-06 09:59:16Z

3

If you want to make a copy of your attributes in a new object, you must use the following (Specific to ActiveRecord) :

obj2 = obj1.dup

This leaves out id, (created|updated)_(at|on) from being duplicated. Also remember that the parent associations live as is in the new object.

answered Feb 6, 2018 at 9:59

bitsapien

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Comments

ndnenkov · Accepted Answer · 2018-02-06 10:01:09Z

3

Simply remove the id:

obj2 = Post.new obj1.attributes.except('id')

Alternatively, use #dup:

obj2 = obj1.dup

answered Feb 6, 2018 at 9:56

ndnenkov

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Thanks. But I did that actually. But I don't want to add except everywhere. Isn't this is a property of new method to create a new object?

@MukarramAli check out #dup.