Samples.ValidatingDuringDeserialization

Validating during deserialization

By manipulating the list of node deserializers, it is easy to add behavior to the deserializer. This example shows how to validate the objects as they are deserialized.

Code

using System;
using System.ComponentModel.DataAnnotations;
using System.IO;
using System.Linq;
using Xunit;
using Xunit.Abstractions;
using YamlDotNet.Core;
using YamlDotNet.Serialization;
using YamlDotNet.Serialization.NodeDeserializers;
using YamlDotNet.Samples.Helpers;

namespace YamlDotNet.Samples
{
    public class ValidatingDuringDeserialization
    {
        private readonly ITestOutputHelper output;

        public ValidatingDuringDeserialization(ITestOutputHelper output)
        {
            this.output = output;
        }

        // First, we'll implement a new INodeDeserializer
        // that will decorate another INodeDeserializer with validation:
        public class ValidatingNodeDeserializer : INodeDeserializer
        {
            private readonly INodeDeserializer _nodeDeserializer;

            public ValidatingNodeDeserializer(INodeDeserializer nodeDeserializer)
            {
                _nodeDeserializer = nodeDeserializer;
            }

            public bool Deserialize(IParser parser, Type expectedType, Func<IParser, Type, object> nestedObjectDeserializer, out object value)
            {
                if (_nodeDeserializer.Deserialize(parser, expectedType, nestedObjectDeserializer, out value))
                {
                    var context = new ValidationContext(value, null, null);
                    Validator.ValidateObject(value, context, true);
                    return true;
                }
                return false;
            }
        }

        [Sample(
            DisplayName = "Validating during deserialization",
            Description = @"
                By manipulating the list of node deserializers,
                it is easy to add behavior to the deserializer.
                This example shows how to validate the objects as they are deserialized.
            "
        )]
        public static void Main()
        {
            // Then we wrap the existing ObjectNodeDeserializer
            // with our ValidatingNodeDeserializer:
            var deserializer = new DeserializerBuilder()
                .WithNodeDeserializer(inner => new ValidatingNodeDeserializer(inner), s => s.InsteadOf<ObjectNodeDeserializer>())
                .Build();

            // This will fail with a validation exception
            var ex = Assert.Throws<YamlException>(() =>
                deserializer.Deserialize<Data>(new StringReader(@"Name: ~"))
            );

            Assert.IsType<ValidationException>(ex.InnerException);
        }
    }

    public class Data
    {
        [Required]
        public string Name { get; set; }
    }
}

Output