可以定义自定义＆＃34; list-merge＆＃34; startegy用于JsonConvert.PopulateObject方法？
示例：
我有两种模式：
class Parent
{
public Guid Uuid { get; set; }
public string Name { get; set; }
public List<Child> Childs { get; set; }
}
class Child
{
public Guid Uuid { get; set; }
public string Name { get; set; }
public int Score { get; set; }
}
我最初的JSON：
{
"Uuid":"cf82b1fd-1ca0-4125-9ea2-43d1d71c9bed",
"Name":"John",
"Childs":[
{
"Uuid":"96b93f95-9ce9-441d-bfb0-f44b65f7fe0d",
"Name":"Philip",
"Score":100
},
{
"Uuid":"fe7837e0-9960-4c45-b5ab-4e4658c08ccd",
"Name":"Peter",
"Score":150
},
{
"Uuid":"1d2cdba4-9efb-44fc-a2f3-6b86a5291954",
"Name":"Steve",
"Score":80
}
]
}
和我的更新JSON：
{
"Uuid":"cf82b1fd-1ca0-4125-9ea2-43d1d71c9bed",
"Childs":[
{
"Uuid":"fe7837e0-9960-4c45-b5ab-4e4658c08ccd",
"Score":170
}
]
}
我需要的是指定一个用于匹配列表项的模型属性（按属性）（在我的例子中是Child的Uuid属性），因此调用从我的反序列化的对象上的JsonConvert.PopulateObject带有更新JSON的初始JSON（它只包含每个对象的更改值+ Uuids）结果只更新由Uuid（在我的情况下更新Peter的得分）的更新JSON中包含的列表元素和未包含在内的元素更新JSON保持不变。
我正在寻找一些通用解决方案 - 我需要将它应用于具有大量嵌套列表的大型JSON（但每个模型都有一些独特的属性）。所以我需要在匹配的列表项上递归调用PopulateObject。
答案 0 :(得分：3)
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existingValue参数，该参数包含要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正在使用的IContractResolver。拥有它可以更容易地找到关键参数，并且还可以确保，如果关键参数具有[JsonProperty(name)]属性，则会更改替换名称。
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; }
}
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);
}
转换器假定密钥参数始终存在于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，则它们将附加到列表中。
<强>更新
原始转换器专门针对List<T>进行了硬编码，并利用List<T>同时实现IList<T>和IList这一事实。如果您的收藏集不是List<T>但仍然实施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。