Scalars

Specification

Scalars are created as instances of ScalarType.

Built-in

These are provided as static properties on ScalarType.

• ScalarType.Boolean
• ScalarType.Int
• ScalarType.ID
• ScalarType.Float
• ScalarType.String

In addition following non-null instances are provided for convenience.

• ScalarType.NonNullBoolean
• ScalarType.NonNullInt
• ScalarType.NonNullID
• ScalarType.NonNullFloat
• ScalarType.NonNullString

Also standard collection is provided

Standard =
            new List<(ScalarType Type, IValueConverter Converter)>()
            {
                (String, new StringConverter()),
                (Int, new IntConverter()),
                (Float, new DoubleConverter()),
                (Boolean, new BooleanConverter()),
                (ID, new IdConverter())
            }

Custom scalars

Create instance of ScalarType and provide name and metadata. Value converter is also needed when building schema with custom scalar in it.

Example:

Scalar:

ID = new ScalarType(
            "ID",
            "The ID scalar type represents a unique identifier, often used to refetch an object" +
            " or as the key for a cache. The ID type is serialized in the same way as a String; " +
            "however, it is not intended to be human‐readable. While it is often numeric, it " +
            "should always serialize as a String.")

Converter:

using System;
using System.Globalization;
using System.Text;
using Tanka.GraphQL.Language.Nodes;


namespace Tanka.GraphQL.TypeSystem.ValueSerialization
{
    public class IdConverter : IValueConverter
    {
        public object? Serialize(object? value)
        {
            if (value == null)
                return null;

            return Convert.ToString(value, CultureInfo.InvariantCulture);
        }

        public ValueBase SerializeLiteral(object? value)
        {
            var serializedValue = Serialize(value);
            if (serializedValue == null)
                return new NullValue();

            return new StringValue(Encoding.UTF8.GetBytes((string)serializedValue));
        }

        public object? ParseValue(object? input)
        {
            if (input == null)
                return null;

            return Convert.ToString(input, CultureInfo.InvariantCulture);
        }

        public object? ParseLiteral(ValueBase input)
        {
            if (input.Kind == NodeKind.NullValue)
            {
                return null;
            }

            if (input.Kind == NodeKind.StringValue) 
                return (StringValue)input.ToString();

            throw new FormatException(
                $"Cannot coerce Id value from '{input.Kind}'");
        }
    }
}