/// <inheritdoc />
/// <remarks>
/// - Methodology
/// - Is the type Two-Way bindable and has the type of the object written into the json? If yes then strip
/// out the type information and ask Json.net to deserialize into that type. If not then...
/// - Get all child types of the specified type.
/// - Filter to child types where every 1st level JSON property is either a public (accessor is public)
/// property or a public field of the child type, using case-insensitive matching. Child types passing
/// this filter are called 'candidates'.
/// - If there are no candidates, then throw.
/// - For all candidates, ask the serializer to deserialize the JSON as the candidate type. Catch and
/// ignore exceptions when attempting to deserialize. If only one candidate successfully deserializes
/// then return the deserialized object.
/// - If more than one candidate successfully deserializes, then filter to candidates whose public
/// properites and fields are all 1st level JSON properties, using case-insensitive matching. We call
/// this "strict matching." If only one candidate has a strict match, return the corresponding
/// deserialized object. Otherwise, throw.
/// - Using the serializer to deserialize enables the method to support types with constructors,
/// which JSON.net does well out-of-the-box and which would be cumbersome to emulate.
/// - This method does not consider > 1st level JSON properties to determine candidates. In other words,
/// it is not matching on the fields/properties of the child's fields/properties (e.g. the match is done
/// on Dog.Owner, not Dog.Owner.OwnersAddress). The issue is that that kind of matching would require
/// complex logic. For example, Strings have properties such as Length which would need to be ignored
/// when reflecting. Similarly, all fields/properties of value-types would need to be ignored. There
/// are likely other corner-cases. To keep things simple, if the 1st level properties match the type's
/// properties and fields, by name, we hand-off the problem to the serializer and let it throw if
/// there is some incompatability deep in the field/property hierarchy.
/// - This method does not consider the type of objects containted within JSON arrays to determine
/// candidates. This is difficult because JSON arrays can contain a mix of types (just likes .net
/// objects) and every element would have to be deserialized and matched against the child's IEnumerable
/// type and undoubtedly complexity would arise from dealing with generics and the vast implementations
/// of IEnumerable. Like the bullet above, we simply hand-off the problem to the serializer.
/// - If properties or fields are removed from a child type after it has been serialized, then the JSON
/// will not deserialize properly because that child type will no longer be a candidate. If, however,
/// properties or fields are added to the child type, then the child type will continue to be a
/// candidate for the serialized JSON.
/// - If the user serializes private or internal fields/properties, then this method will not work because
/// it only looks for public fields/properties. We cannot bank on the JSON having been serialized by
/// the same serializer passed to this method. Even if we could, the serializer is so highly
/// configurable that it would be difficult to determine whether or which internal or private fields
/// or properties are serialized.
/// - It's OK if the JSON is serialized with NullValueHandling.Ignore because the candidate filter tries
/// to find all JSON properties in child type's properties/fields, and not vice-versa. However, depending
/// on how permissive the serializer's Contract Resolver is, those candidates may or may not be able to
/// be deserialized. For example, if constructor parameters are required and a particular parameter is
/// excluded from the JSON, then that type cannot be deserialized.
/// </remarks>
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
if (reader == null)
{
throw new ArgumentNullException("reader");
}
if (serializer == null)
{
throw new ArgumentNullException("serializer");
}
if (reader.TokenType == JsonToken.Null)
{
return(null);
}
var jsonObject = JObject.Load(reader);
var jsonProperties = new HashSet <string>(GetProperties(jsonObject), StringComparer.OrdinalIgnoreCase);
// if two-way bindable then then type should be written into the json
// if it's not then fallback on the typical strategy
var bindableAttribute = GetBindableAttribute(objectType);
if (IsTwoWayBindable(bindableAttribute) && jsonProperties.Contains(TypeTokenName))
{
return(ReadUsingTypeSpecifiedInJson(serializer, jsonObject));
}
var childTypes = GetChildTypes(objectType);
var candidateChildTypes = GetCandidateChildTypes(childTypes, jsonProperties);
var deserializedChildren = DeserializeCandidates(candidateChildTypes, serializer, jsonObject).ToList();
if (deserializedChildren.Count == 0)
{
throw new JsonSerializationException(
string.Format(CultureInfo.InvariantCulture, "Unable to deserialize to type {0}, value: {1}", objectType, jsonObject));
}
CandidateChildType matchedChild = null;
if (deserializedChildren.Count == 1)
{
matchedChild = deserializedChildren.Single();
}
else if (deserializedChildren.Count > 1)
{
matchedChild = SelectBestChildUsingStrictPropertyMatching(deserializedChildren, jsonObject, jsonProperties);
}
return(matchedChild.DeserializedObject);
}
private static IEnumerable <CandidateChildType> GetCandidateChildTypes(IEnumerable <Type> childTypes, HashSet <string> jsonProperties)
{
var candidateChildTypes = new List <CandidateChildType>();
foreach (var childType in childTypes)
{
var childTypeProperties = childType.GetProperties().Select(t => t.Name).ToList();
var childTypeFields = childType.GetFields().Select(t => t.Name).ToList();
var childTypePropertiesAndFields = new HashSet <string>(
childTypeProperties.Concat(childTypeFields),
StringComparer.OrdinalIgnoreCase);
if (jsonProperties.All(p => childTypePropertiesAndFields.Contains(p)))
{
var candidateChildType = new CandidateChildType
{
Type = childType,
PropertiesAndFields = childTypePropertiesAndFields
};
candidateChildTypes.Add(candidateChildType);
}
}
return(candidateChildTypes);
}
