CODEWITHSUNDEEP
ruby-on-rails-3activerecordrails-models
EugeneM
EugeneM

Reputation: 11

How does rails come up with the ID for a new model/record?

How does activerecord assign an ID to a newly created record? The ID values seem to be all over the place. Sometimes they are sequential, but sometimes they seem to be some kind of a hash. Is there a way to control the behavior?

Upvotes: 1

Views: 181

Answers (1)

Ryan Bigg
Ryan Bigg

Reputation: 107728

Within a relational database you'll see that IDs are usually sequential. This happens to be an automatically incrementing field called id by default in these databases with Rails. This is the 99% case, meaning that 99% of the time you can expect to see it done this way. It's the sane way.

However, There are some cases in which the "id" field within the database may not be automatically incrementing and may instead be a string. In a database I am working with at the moment, the id field is called client_id, is a 6-character string such as "RAB001" and needs to be manually assigned by the code itself. This is due to a legacy system we are supporting and there's nothing we can do to fix that. It's just how it is.

In other databases such as Mongoid the ids are, once again, generated automatically. There's a difference here though: instead of them being automatically incrementing numbers they are a hash. In a Mongo database I happen to have handy, one of the object's _id fields (note the underscore) is this lovely, easy-to-understand1 hash: 4e22b5812f8b7d6f6d000001. This is automatically generated by Mongo and I don't really care what it is except for when I need to find an object and there's no other way of finding it by another unique value.

I would recommend sticking with an automatically generating ID system, be it something provided by the traditional database systems such as PostgreSQL or MySQL or something by Mongo.

Any system where you need to generate the primary key for a record manually needs to have a huge "HERE BE DRAGONS" label on it and should be handled like a case of nitroglycerin or similarly to this apt analogy. Avoid this system if you can.

1 I am being sarcastic here.

Upvotes: 1

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