您可以创建自己的JsonConverter 来实现所需的合并逻辑。这是可能的，因为 JsonConverter.ReadJson 传递了一个 existingValue 参数，其中包含正在反序列化的属性的预先存在的内容。
因此：
[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = false)]
public class JsonMergeKeyAttribute : System.Attribute
{
}
public class KeyedListMergeConverter : JsonConverter
{
readonly IContractResolver contractResolver;
public KeyedListMergeConverter(IContractResolver contractResolver)
{
if (contractResolver == null)
throw new ArgumentNullException("contractResolver");
this.contractResolver = contractResolver;
}
static bool CanConvert(IContractResolver contractResolver, Type objectType, out Type elementType, out JsonProperty keyProperty)
{
elementType = objectType.GetListType();
if (elementType == null)
{
keyProperty = null;
return false;
}
var contract = contractResolver.ResolveContract(elementType) as JsonObjectContract;
if (contract == null)
{
keyProperty = null;
return false;
}
keyProperty = contract.Properties.Where(p => p.AttributeProvider.GetAttributes(typeof(JsonMergeKeyAttribute), true).Count > 0).SingleOrDefault();
return keyProperty != null;
}
public override bool CanConvert(Type objectType)
{
Type elementType;
JsonProperty keyProperty;
return CanConvert(contractResolver, objectType, out elementType, out keyProperty);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
if (contractResolver != serializer.ContractResolver)
throw new InvalidOperationException("Inconsistent contract resolvers");
Type elementType;
JsonProperty keyProperty;
if (!CanConvert(contractResolver, objectType, out elementType, out keyProperty))
throw new JsonSerializationException(string.Format("Invalid input type {0}", objectType));
if (reader.TokenType == JsonToken.Null)
return existingValue;
var list = existingValue as IList;
if (list == null || list.Count == 0)
{
list = list ?? (IList)contractResolver.ResolveContract(objectType).DefaultCreator();
serializer.Populate(reader, list);
}
else
{
var jArray = JArray.Load(reader);
var comparer = new KeyedListMergeComparer();
var lookup = jArray.ToLookup(i => i[keyProperty.PropertyName].ToObject(keyProperty.PropertyType, serializer), comparer);
var done = new HashSet<JToken>();
foreach (var item in list)
{
var key = keyProperty.ValueProvider.GetValue(item);
var replacement = lookup[key].Where(v => !done.Contains(v)).FirstOrDefault();
if (replacement != null)
{
using (var subReader = replacement.CreateReader())
serializer.Populate(subReader, item);
done.Add(replacement);
}
}
// Populate the NEW items into the list.
if (done.Count < jArray.Count)
foreach (var item in jArray.Where(i => !done.Contains(i)))
{
list.Add(item.ToObject(elementType, serializer));
}
}
return list;
}
public override bool CanWrite { get { return false; } }
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
class KeyedListMergeComparer : IEqualityComparer<object>
{
#region IEqualityComparer<object> Members
bool IEqualityComparer<object>.Equals(object x, object y)
{
if (object.ReferenceEquals(x, y))
return true;
else if (x == null || y == null)
return false;
return x.Equals(y);
}
int IEqualityComparer<object>.GetHashCode(object obj)
{
if (obj == null)
return 0;
return obj.GetHashCode();
}
#endregion
}
}
public static class TypeExtensions
{
public static Type GetListType(this Type type)
{
while (type != null)
{
if (type.IsGenericType)
{
var genType = type.GetGenericTypeDefinition();
if (genType == typeof(List<>))
return type.GetGenericArguments()[0];
}
type = type.BaseType;
}
return null;
}
}
请注意，转换器需要知道当前使用的IContractResolver。拥有它可以更轻松地找到关键参数，并且还可以确保，如果关键参数具有 [JsonProperty(name)] 属性，则替换名称受到尊重。
然后添加属性：
class Child
{
[JsonMergeKey]
[JsonProperty("Uuid")] // Replacement name for testing
public Guid UUID { get; set; }
public string Name { get; set; }
public int Score { get; set; }
}
并按如下方式使用转换器：
var serializer = JsonSerializer.CreateDefault();
var converter = new KeyedListMergeConverter(serializer.ContractResolver);
serializer.Converters.Add(converter);
using (var reader = new StringReader(updateJson))
{
serializer.Populate(reader, parent);
}
转换器假定关键参数始终存在于 JSON 中。此外，如果要合并的 JSON 中的任何条目具有在现有列表中找不到的键，它们将被附加到列表中。
更新
原始转换器专门为List<T> 硬编码，并利用List<T> 实现IList<T> 和IList 的事实。如果您的集合不是 List<T> 但仍实现 IList<T>，则以下内容应该有效：
public class KeyedIListMergeConverter : JsonConverter
{
readonly IContractResolver contractResolver;
public KeyedIListMergeConverter(IContractResolver contractResolver)
{
if (contractResolver == null)
throw new ArgumentNullException("contractResolver");
this.contractResolver = contractResolver;
}
static bool CanConvert(IContractResolver contractResolver, Type objectType, out Type elementType, out JsonProperty keyProperty)
{
if (objectType.IsArray)
{
// Not implemented for arrays, since they cannot be resized.
elementType = null;
keyProperty = null;
return false;
}
var elementTypes = objectType.GetIListItemTypes().ToList();
if (elementTypes.Count != 1)
{
elementType = null;
keyProperty = null;
return false;
}
elementType = elementTypes[0];
var contract = contractResolver.ResolveContract(elementType) as JsonObjectContract;
if (contract == null)
{
keyProperty = null;
return false;
}
keyProperty = contract.Properties.Where(p => p.AttributeProvider.GetAttributes(typeof(JsonMergeKeyAttribute), true).Count > 0).SingleOrDefault();
return keyProperty != null;
}
public override bool CanConvert(Type objectType)
{
Type elementType;
JsonProperty keyProperty;
return CanConvert(contractResolver, objectType, out elementType, out keyProperty);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
if (contractResolver != serializer.ContractResolver)
throw new InvalidOperationException("Inconsistent contract resolvers");
Type elementType;
JsonProperty keyProperty;
if (!CanConvert(contractResolver, objectType, out elementType, out keyProperty))
throw new JsonSerializationException(string.Format("Invalid input type {0}", objectType));
if (reader.TokenType == JsonToken.Null)
return existingValue;
var method = GetType().GetMethod("ReadJsonGeneric", BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public);
var genericMethod = method.MakeGenericMethod(new[] { elementType });
try
{
return genericMethod.Invoke(this, new object[] { reader, objectType, existingValue, serializer, keyProperty });
}
catch (TargetInvocationException ex)
{
// Wrap the TargetInvocationException in a JsonSerializationException
throw new JsonSerializationException("ReadJsonGeneric<T> error", ex);
}
}
object ReadJsonGeneric<T>(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer, JsonProperty keyProperty)
{
var list = existingValue as IList<T>;
if (list == null || list.Count == 0)
{
list = list ?? (IList<T>)contractResolver.ResolveContract(objectType).DefaultCreator();
serializer.Populate(reader, list);
}
else
{
var jArray = JArray.Load(reader);
var comparer = new KeyedListMergeComparer();
var lookup = jArray.ToLookup(i => i[keyProperty.PropertyName].ToObject(keyProperty.PropertyType, serializer), comparer);
var done = new HashSet<JToken>();
foreach (var item in list)
{
var key = keyProperty.ValueProvider.GetValue(item);
var replacement = lookup[key].Where(v => !done.Contains(v)).FirstOrDefault();
if (replacement != null)
{
using (var subReader = replacement.CreateReader())
serializer.Populate(subReader, item);
done.Add(replacement);
}
}
// Populate the NEW items into the list.
if (done.Count < jArray.Count)
foreach (var item in jArray.Where(i => !done.Contains(i)))
{
list.Add(item.ToObject<T>(serializer));
}
}
return list;
}
public override bool CanWrite { get { return false; } }
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
class KeyedListMergeComparer : IEqualityComparer<object>
{
#region IEqualityComparer<object> Members
bool IEqualityComparer<object>.Equals(object x, object y)
{
return object.Equals(x, y);
}
int IEqualityComparer<object>.GetHashCode(object obj)
{
if (obj == null)
return 0;
return obj.GetHashCode();
}
#endregion
}
}
public static class TypeExtensions
{
public static IEnumerable<Type> GetInterfacesAndSelf(this Type type)
{
if (type == null)
throw new ArgumentNullException();
if (type.IsInterface)
return new[] { type }.Concat(type.GetInterfaces());
else
return type.GetInterfaces();
}
public static IEnumerable<Type> GetIListItemTypes(this Type type)
{
foreach (Type intType in type.GetInterfacesAndSelf())
{
if (intType.IsGenericType
&& intType.GetGenericTypeDefinition() == typeof(IList<>))
{
yield return intType.GetGenericArguments()[0];
}
}
}
}
请注意，数组没有实现合并，因为它们不可调整大小。