Just a quick note — when creating foreign keys in a Rails 5.1+ you should make sure to they are typed as bigint. 

But why?

Starting in Rails 5.1 primary keys were defaulted to bigint.  Check this commit from 2016.  This means that referential foreign keys also need to be bigint.  If you’ve gotten into the habit of rails g model Whatever user_id:integer,you need to break it. 

Use user:references or user:belongs_to (which is an alias of references) instead.  These will automatically use bigint and all will be well.

But why???

If you forget to do this or use some kind of gem that generates an integer foreign key your app won’t break yet…

The issue is rooted in this bit I stole from the PostgreSQL docs:

bigint is yuge and as a result you could run into a situation where the primary key (a bigint) you’re trying to persist is bigger than the FK column (an integer) can hold.

Here’s a nice snippet that can be used in a PostgreSQL database to output the current database’s size.

SELECT pg_size_pretty(pg_database_size(current_database())) AS human_size, 
       pg_database_size(current_database())                 AS raw_size;

That statement will output something along the lines of:

human_size  | raw_size
------------+--------------
181 GB      | 193841573064

Here’s an awesome Toy Story inspired mnemonic device for remembering the proper use of Rails’ `has_one` associations.

Andy “has_one” Woody.

Woody “belongs_to” Andy.

Where is the foreign key? On Woody’s sole!

Credit goes to Stack Overflow user “mike” from a comment on a related topic.

I use Postgres.app to run a local Postgres server while doing development work and it’s great. Postgres.app basically provides a completely contained pg server that’s ready to go out of the box — just launch the app and you’re good to go.

Unfortunately because it’s a self contained app things are installed in non-standard places.

More specifically, while installing the `pg` gem on a system I recently had it fail with this error:Continue reading

I recently setup my development system from scratch and one of the tasks is installing PostgreSQL as my apps are almost always deployed to Heroku and they <3 PG.

As you may or may not know, Lion ships with a castrated Postgres installation which (if you don’t already know this (!!!!)) can make it challenging to use something like Homebrew for your installation medium.

To avoid this whole situation I suggest you checkout Postgres.app.  It’s written by the guys @ Heroku and is essentially a .app that you drop in your Applications folder.  Run whenever you want a PG server — it’s THAT easy.

Well… Sorta…

After installing it I had some issues but was able to figure it out so that’s really the “gotcha” part of this post.

On first launch i realized i couldn’t connect to the PG server and immediately went to my system’s console for clues.  This was sitting there looking pretty:

Ye olde  “Failed system call was shmget” error….

I believe the root of this issue is that OSX’s shared memory configuration is just really small. And after Googling around I found this post on Railscasts.com by Denis Savitsky (aka sadfuzzy).

In a nut shell there are two ways to fix this:

1- Temporary Solution: Gone after reboot.

2- Permanent Solution: Forever, forever, ever, forever, ever? Yep. After reboot the settings will stick.

You can also see this post for further details.

Just a quick note:

Backup: $ pg_dump -U {user-name} {source_db} -f {dumpfilename.sql}
Restore: $ psql -U {user-name} -d {desintation_db} -f {dumpfilename.sql}

Lifted from this great post @ TGS