How to use the value of a variable to access a class property in c#?

Question

i have a class like this :

public class Wallet
{
    public int Id { get; set; }

    public decimal Doge { get; set; }

    public decimal Bitcoin { get; set; }

    public decimal Ethereum { get; set; }

    public decimal Tether { get; set; }
}

When the user makes a request for withdrawal or deposit, I have to check the type of currency with the switch case statement and perform the operation. Like this:

private static void CalculateOrder(Order order, Order offer, bool isBuy, string coin)
{
    var sign = -1;
    if (isBuy)
        sign = 1;

    switch (coin)
    {
        case SC.Ethereum:
            {
                order.ApplicationUser.Wallet.Ethereum += sign * (order.Amount);
                offer.ApplicationUser.Wallet.Ethereum -= sign * (order.Amount);
                break;
            }
        case SC.Bitcoin:
            {
                order.ApplicationUser.Wallet.Bitcoin += sign * (order.Amount);
                offer.ApplicationUser.Wallet.Bitcoin -= sign * (order.Amount);
                break;
            }
        case SC.Doge:
            {
                order.ApplicationUser.Wallet.Doge += sign * (order.Amount);
                offer.ApplicationUser.Wallet.Doge -= sign * (order.Amount);
                break;
            }
    }
}

I'm sure the value of the coin variable is the same as the wallet class properties.

Now how can I directly access one of the properties of the same name with a variable value of coin without switch statement ?

In JavaScript, if we have an object like this :

const restaurant = {

  name: 'Classico Italiano',

  openingHours: {
    thu: {
      open: 12,
      close: 22,
    },
    fri: {
      open: 11,
      close: 23,
    },
    sat: {
      open: 0, // Open 24 hours
      close: 24,
    },
  },

};

we can access to opening days like below :

const days = ['mon', 'tue', 'wed', 'thu', 'fri', 'sat', 'sun'];

for (const day of days) {
  const open = restaurant.openingHours[day] ?? 'closed';
  console.log(`On ${day}, we ${open}`);
}

Or something like what is said in this post

Is there such a thing in C #?

use a dictioanary to store amount as value and the currency as key, wallet class can have this dictionary as a property — Mehrdad Dowlatabadi
– Mehrdad Dowlatabadi, Commented Sep 17, 2021 at 19:43

Robert McKee · Accepted Answer · 2021-09-17 19:53:18Z

2

The same way you would in javascript. You make the Wallet a dictionary that uses a string as an index, and returns a decimal.

It would probably be better if you used an enumeration instead of a string though.

public enum CoinTypes { Etherium, Bitcoin, Doge };
public class Wallet {
  public int id {get;set;}
  public Dictionary<CointTypes,decimal> Coins {get;set;} = new Dictionary<CoinTypes,decimal>();
}
private static void CalculateOrder(Order order, Order offer, bool isBuy, string coin)
{
    var sign = -1;
    if (isBuy)
        sign = 1;
    var c = Enum.Parse(typeof(CoinTypes), coins);
    order.ApplicationUser.Wallet[c] += sign * (order.Amount);
    offer.ApplicationUser.Wallet[c] -= sign * (order.Amount);
}

edited Sep 17, 2021 at 19:53

answered Sep 17, 2021 at 19:40

Robert McKee

21.5k1 gold badge48 silver badges64 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

MohanmadJavad Jamali Over a year ago

Wallet class is a database model . Is it possible to use the dictionary type to property a database model? I tried but failed.

Robert McKee Over a year ago

Typically you would not, but you can model the Wallet so that it contains a List, and then you can look up the correct CoinType by iterating through the list. Such as:

public class Wallet { public int id {get;set;} public List<WalletCoins> Coins {get;set;} } public class WalletCoins { public int id {get;set;} public CoinTypes CoinType {get;set;} public decimal Amount {get;set;}}

Robert McKee Over a year ago

Then you can: order.ApplicationUser.Wallet.Coins.First(z => z.CoinType == c).Amount += ... the performance difference between linearly searching a list and using a dictionary is going to be trivial when the list/dictionary only contains a few elements anyhow.

NetMage · Accepted Answer · 2021-09-21 20:14:46Z

You can use the specific class with properties if you create some interface methods to access properties via their name as a string.

In general, you can use lambda methods in C# in place of string property accessors in other languages. Creating a static Dictionary would not be ideal as it would need to be updated each time a new coin type was added. Instead, you can use Reflection to initialize the Dictionary.

You need a helper extension method to use Reflection to get the properties (or fields):

public static List<MemberInfo> GetPropertiesOrFields(this Type t, BindingFlags bf = BindingFlags.Public | BindingFlags.Instance) =>
    t.GetMembers(bf).Where(mi => mi.MemberType == MemberTypes.Field || mi.MemberType == MemberTypes.Property).ToList();

Then you can initialize the Dictionary:

public static Dictionary<string, (Action<Wallet,decimal> add, Action<Wallet,decimal> subt)> CoinField = new();
public void AddAmount(string coinType, decimal amount) => CoinField[coinType].add(this,amount);
public void SubtractAmount(string coinType, decimal amount) => CoinField[coinType].subt(this,amount);

static Wallet() {
    var coinProps = typeof(Wallet).GetPropertiesOrFields().Where(p => p.GetMemberType() == typeof(decimal));
    foreach (var coinProp in coinProps) {
        var coinName = coinProp.Name;
        CoinField.Add(coinName, (coinAdder(coinName), coinSubter(coinName)));
    }
}

static Action<Wallet, decimal> coinAdder(string coinType) {
    var pW = Expression.Parameter(typeof(Wallet), "w");
    var pAmt = Expression.Parameter(typeof(decimal), "amt");
    var propCoin = Expression.PropertyOrField(pW, coinType);
    var body = Expression.AddAssign(propCoin, pAmt);
    return Expression.Lambda<Action<Wallet, decimal>>(body, pW, pAmt).Compile();
}

static Action<Wallet, decimal> coinSubter(string coinType) {
    var pW = Expression.Parameter(typeof(Wallet), "w");
    var pAmt = Expression.Parameter(typeof(decimal), "amt");
    var propCoin = Expression.PropertyOrField(pW, coinType);
    var body = Expression.SubtractAssign(propCoin, pAmt);
    return Expression.Lambda<Action<Wallet, decimal>>(body, pW, pAmt).Compile();
}

Then CalculateOrder is simply:

private static void CalculateOrder(Order order, Order offer, bool isBuy, string coin) {
    var sign = isBuy ? 1 : -1;
    order.ApplicationUser.Wallet.AddAmount(coin, sign * order.Amount);
    offer.ApplicationUser.Wallet.SubtractAmount(coin, sign * order.Amount);
}

However, you could also use Reflection directly to access the properties.

public void AddAmount(string coinType, decimal amount) {
    var propInfo = typeof(Wallet).GetProperty(coinType);
    var curValue = (decimal)propInfo.GetValue(this);
    curValue += amount;
    propInfo.SetValue(this, curValue);
}
public void SubtractAmount(string coinType, decimal amount) {
    var propInfo = typeof(Wallet).GetProperty(coinType);
    var curValue = (decimal)propInfo.GetValue(this);
    curValue -= amount;
    propInfo.SetValue(this, curValue);
}

This will cause a runtime exception if the coinType doesn't match a valid property name.

If speed is very important, you could cache the MemberInfo values or pre-load them similar to the lambda Dictionary above.

static Dictionary<string,MemberInfo> CoinPropInfos = new();    
static Wallet() {
    CoinPropInfos = typeof(Wallet).GetPropertiesOrFields().Where(p => p.GetMemberType() == typeof(decimal)).ToDictionary(p => p.Name);
}

public void AddAmount(string coinType, decimal amount) {
    var propInfo = CoinPropInfos[coinType];
    var curValue = (decimal)propInfo.GetValue(this);
    curValue += amount;
    propInfo.SetValue(this, curValue);
}
public void SubtractAmount(string coinType, decimal amount) {
    var propInfo = CoinPropInfos[coinType];
    var curValue = (decimal)propInfo.GetValue(this);
    curValue -= amount;
    propInfo.SetValue(this, curValue);
}

Collectives™ on Stack Overflow

How to use the value of a variable to access a class property in c#?

2 Answers 2

3 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related