feat(errors): add unique constraint violation error

[steebchen]

Adds helper functions for one of the most commonly used errors, a unique constraint violation.

Note that different databases return slightly different metadata, which means the implementation details depend on what database you use:

user, err := db.User.CreateOne(...).Exec(cxt)
if err != nil {
	if info, err := db.IsErrUniqueConstraint(); err != nil {
		// Fields exists for Postgres and SQLite
		log.Printf("unique constraint on the fields: %s", info.Fields)

		// you can also compare it with generated field names:
		if info.Fields[0] == db.User.Name.Field() {
			// do something
		}

		// For MySQL and MongoDB, use the constraint key
		log.Printf("unique constraint on the key: %s", info.Key)
	}
}

fix #213

[nettrino]

@steebchen is this OK to be merged? would help a lot with error handling

[steebchen]

@nettrino Actually it would be great if you could try it using

go get github.com/steebchen/prisma-client-go@c1a00401061ebbb46e41033b620d9fafa5896204

and re-generate the client.

This PR includes some tests but it would be great for someone to actually use it and check if everything looks good. Thanks! Feel free to ping me in discord as well.

[ytsruh]

Tested on Postgres (Neon DB) tonight and it works fine for me. Unique constraints on both BigInt & String types work as expected. Thanks for this!

[nettrino]

@steebchen Has also been running fine for me for a week or so, so this should be good to merge!

[steebchen]

Awesome thanks! One thing which @abelanger5 mentioned is that it would be nice if errors.As would work, which it doesn't right now. It needs some refactor though and some extra work, so I'll just merge this as is and anything else can be an extra improvement.