UI bindings? about rxgrdb HOT 5 CLOSED

Hello @robert-cronin,

Your sample code looks like you want to drive the content of the database from a textfield. But is it really the case? Don't you want instead to have the content of the database drive the UI?

If this is the case, then the code below, inspired from RxSwift sample code, should work as expected:

// Number of players
let allPlayersRequest = Player.all()
allPlayersRequest.rx
    .fetchCount(in: dbQueue)
    .map { "\($0) players" }
    .bind(to: playerCountLabel.rx.text)

// Maximum score
let maximumScoreRequest = Player
    .select(max(Column("score")))
    .asRequestOf(Int.self)
maximumScoreRequest.rx
    .fetchOne(in: dbQueue)
    .map { "\($0 ?? 0)" }
    .bind(to: maximumScoreLabel.rx.text)

// Name of player 1
Player.filter(key: 1).rx
    .fetchOne(in: dbQueue)
    .map { $0?.name ?? "" }
    .bind(to: playerNameLabel.rx.text)

Now of course, you may sometimes need to update several UI elements on each database change. For example, if you track a single record, you may write something like:

Player.filter(key: 1).rx
    .fetchOne(in: dbQueue)
    .subscribe(onNext: { player in
        if player = player {
            // Update UI for updated Player 1
        } else {
            // Update UI for deleted Player 1
        }
    })

from rxgrdb.

Oh, and I have to give you an extra advice when I read:

FLIGHTS.filter(sql: "FLIGHT_ID = '\(currentFlightID)'")

You should really stop embedding raw values in SQL, and start using arguments instead:

FLIGHTS.filter(sql: "FLIGHT_ID = ?", arguments: [currentFlightID})

Another valid option:

FLIGHTS.filter(Column("FLIGHT_ID") == currentFlightID)

Sorry if I sound like a pontificating teacher, but this has to become a reflex: NEVER EMBED RAW VALUES IN YOUR SQL See Avoiding SQL Injection for more information.

from rxgrdb.

Thanks groue!
I have tried to implement a simple binding but keep coming up with the following error:
Fatal error: could not convert database value NULL to String

I have a flights table with an aircraft id i want to bind to a textfield, my implementation looks like this:

FLIGHTS.filter(sql: "FLIGHT_ID = '\(currentFlightID)'").rx
    .fetchOne(in: dbQueue)
    .map { $0?.AC_ID ?? "" }
    .bind(to: aircraftIdText.rx.text)

Any ideas on why this is the case given that I know AC_ID is not null?

Thanks!

from rxgrdb.

Any ideas on why this is the case given that I know AC_ID is not null?

Sure. The error message says that someone has tried to decode a NULL column into a non-optional String.

Even if your code only displays AC_ID, it decodes full Flight objects:

struct Flight {
    var FLIGHT_ID: String // requires non-null FLIGHT_ID column
    var AC_ID: String     // requires non-null AC_ID column
    var PILOT_ID: String  // requires non-null PILOT_ID column
    var NAME: String      // requires non-null NAME column
    ...
}

There are only two ways out:

1. Fix the content of the database: add NOT NULL constraints on columns that must not be null, and find the bug which inserts those invalid nulls.

2. Make optional properties that should accept null columns:

   struct Flight {
       var FLIGHT_ID: String // mandatory
       var AC_ID: String     // mandatory
       var PILOT_ID: String? // Pilot may not be known yet
       var NAME: String      // mandatory
       ...
   }

from rxgrdb.

Yes, I felt a bit nervous writing it like that! It is all functioning as expected now, this library has saved me pages of code! Thanks for writing it 😄

from rxgrdb.