Commit graph

3 commits

Author SHA1 Message Date
William Carroll
8ebc89b44b Remove erroneous parens around columns in SELECT statement
These were causing runtime errors... whoops!
2020-07-30 19:52:04 +01:00
William Carroll
6ecab8c3a6 Prefer SELECT (a,b,c) to SELECT *
"SELECT *" in SQL may not guarantee the order in which a record's columns are
returned. For example, in my FromRow instances for Account, I make successive call

The following scenario silently and erroneously assigns:

firstName, lastName = lastName, firstName

```sql
CREATE TABLE People (
  firstName TEXT NOT NULL,
  lastName TEXT NOT NULL,
  age INTEGER NOT NULL,
  PRIMARY KEY (firstName, lastName)
)
```

```haskell
data Person = Person { firstName :: String, lastName :: String, age :: Integer }

fromRow = do
  firstName <- field
  lastName  <- field
  age       <- field
  pure Person{..}

getPeople :: Connection -> IO [Person]
getPeople conn = query conn "SELECT * FROM People"
```

This silently fails because both firstName and lastName are Strings, and so the
FromRow Person instance type-checks, but you should expect to receive a list of
names like "Wallace William" instead of "William Wallace".

The following won't break the type-checker, but will result in a runtime parsing
error:

```haskell
-- all code from the previous example remains the same except for:

fromRow = do
  age       <- field
  firstName <- field
  lastName  <- field
```

The "SELECT *" will return records like (firstName,lastName,age), but the
FromRow instance for Person will attempt to parse firstName as
Integer.

So... what have we learned? Prefer "SELECT (firstName,lastName,age)" instead of
"SELECT *".
2020-07-30 18:52:45 +01:00
William Carroll
dec8890190 Verify users' email addresses when they attempt to sign-up
Lots of changes here:
- Add the GET /verify endpoint
- Email users a secret using MailGun
- Create a PendingAccounts table and record type
- Prefer do-notation for FromRow instances (and in general) instead of the <*>
  or a liftA2 style. Using instances using `<*>` makes the instances depend on
  the order in which the record's fields were defined. When combined with a
  "SELECT *", which returns the columns in whichever order the schema defines
  them (or depending on the DB implementation), produces runtime parse errors
  at best and silent errors at worst.
- Delete bill from accounts.csv to free up the wpcarro@gmail.com when testing
  the /verify route.
2020-07-30 18:38:46 +01:00