Get ID of Rails Model before saving…?

Question

How do you get the id of a rails model before it is saved?

For example, if I create a new model instance, how can I get its ID before it is saved?

I know t

Answer 1

First understand the structure of database.

• Id is gerated using sequence.
• increament done by 1 (specified while creating sequence)
• Last entry to database will have highest value of id

If you wanted to get id of record which is going to be saved,

Then you can use following:

 1. id = Model.last.id + 1
    model = Model.new(id: id)
    model.save
    # But if data can be delete from that dataabse this will not work correctly.

 2. id = Model.connection.select_value("Select nextval('models_id_seq')")
    model = Model.new(id: id)
    model.save
    # Here in this case if you did not specified 'id' while creating new object, record will saved with next id. 

    e.g. 
    id
    => 2234
    model = Model.new(id: id) 
    model.save 
    # Record will be created using 'id' as 2234  

    model = Model.new()
    model.save
    # Record will be created using next value of 'id' as 2235  

Hope this will help you.