Thursday, July 24, 2014

Escaping '&' (ampersand) in razor view engine


Recently I ran into a really annoying problem with the asp.net razor view engine -
I was generating some url's on the server side, and trying to print them inside html tag attributes like 'href' or 'src'.

The problem was that all the ampersands ('&') were being encoded to '&'.
First thing I tried to do was print it out using the Html 'Raw' helper method, like this :
Some Link


This didn't work... :/
The weird thing about this was that when I searched the internet and found questions on stackoverflow, some people wrote that Html.Raw() worked for them and some said it didn't.

After a little more research (mostly based on some trial & error), I realized that razor will always encode strings inserted in attribute values. This is done for security reasons. The proper workaround is to simply put the whole tag inside the 'Raw()' method, like this:
@Html.Raw("Some Link)


This basically tells razor - "I know what I'm doing, just let me do it my way!" :)

Sunday, July 13, 2014

Saving prices as decimal in mongodb


When working with prices in C#, you should always work with the 'decimal' type.
Working with the 'Double' type can lead to a variety of rounding errors when doing calculations with them, and is more intended for mathematical equations.

(I don't want to go into details about what problems this can cause exactly, but you can read more about it here :
http://stackoverflow.com/questions/2129804/rounding-double-values-in-c-sharp
http://stackoverflow.com/questions/15330988/double-vs-decimal-rounding-in-c-sharp
http://stackoverflow.com/questions/693372/what-is-the-best-data-type-to-use-for-money-in-c
http://pagehalffull.wordpress.com/2012/10/30/rounding-doubles-in-c/ )

I am currently working on a project that involves commerce and prices, so naturally I used 'decimal' for all price types.
Then I headed to my db, which in my case is mongodb, and the problem arose.
MongoDB doesn't support 'decimal'!! It only supports the double type.

Since I rather avoid saving it as a double for reasons stated above, I had to think of a better solution.
I decided to save all the prices in the db as Int32 saving the prices in 'cents'.

This means I just need to multiply the values by 100 when inserting to the db, and dividing by 100 when retrieving. This should never cause any rounding problems, and is pretty much straight-forward. I even don't need to worry about sorting, or any other query for that matter.

But... I don't want ugly code doing all these conversions from cents to dollars in every place...

I'm using the standard C# mongo db driver (https://github.com/mongodb/mongo-csharp-driver), which gives me the ability to write a custom serializer for a specific field.
This is a great solution, since it's the lowest level part of the code that deals with the db, and that means all my entities will be using 'decimal' everywhere.

This is the code for the serializer :
[BsonSerializer(typeof(MongoDbMoneyFieldSerializer))]
public class MongoDbMoneyFieldSerializer : IBsonSerializer
{
    public object Deserialize(BsonReader bsonReader, Type nominalType, IBsonSerializationOptions options)
    {
        var dbData = bsonReader.ReadInt32();
        return (decimal)dbData / (decimal)100;
    }

    public object Deserialize(BsonReader bsonReader, Type nominalType, Type actualType, IBsonSerializationOptions options)
    {
        var dbData = bsonReader.ReadInt32();
        return (decimal)dbData / (decimal)100;
    }

    public IBsonSerializationOptions GetDefaultSerializationOptions()
    {
        return new DocumentSerializationOptions();
    }

    public void Serialize(BsonWriter bsonWriter, Type nominalType, object value, IBsonSerializationOptions options)
    {
        var realValue = (decimal) value;
        bsonWriter.WriteInt32(Convert.ToInt32(realValue * 100));
    }
}


And then all you need to do is add the custom serializer to the fields which are prices, like this:
public class Product
{
    public string Title{ get; set; }
    public string Description { get; set; }

    [BsonSerializer(typeof(MongoDbMoneyFieldSerializer))]
    public decimal Price { get; set; }

    [BsonSerializer(typeof(MongoDbMoneyFieldSerializer))]
    public decimal MemberPrice { get; set; }

    public int Quantity { get; set; }
}

That's all there is to it.