我希望使用 NewtonSoft JSON 对列表进行序列化，我需要在序列化时忽略其中一个属性，我得到了以下代码
public class Car
{
// included in JSON
public string Model { get; set; }
// ignored
[JsonIgnore]
public DateTime LastModified { get; set; }
}
但是我在我的应用程序的许多地方都使用了这个特定的类 Car，我只想在一个地方排除该选项。
我可以在我需要的特定位置动态添加 [JsonIgnore] 吗？我该怎么做？
【问题讨论】：
标签： c# attributes json.net
不需要做其他答案中解释的复杂事情。
NewtonSoft JSON 有一个内置功能：
public bool ShouldSerializeINSERT_YOUR_PROPERTY_NAME_HERE()
{
if(someCondition){
return true;
}else{
return false;
}
}
它被称为“条件属性序列化”和文档can be found here。
警告：首先，删除{get;set;} 属性上方的[JsonIgnore] 很重要。否则它将覆盖ShouldSerializeXYZ 行为。
【讨论】：
我认为最好使用自定义 IContractResolver 来实现：
public class DynamicContractResolver : DefaultContractResolver
{
private readonly string _propertyNameToExclude;
public DynamicContractResolver(string propertyNameToExclude)
{
_propertyNameToExclude = propertyNameToExclude;
}
protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
{
IList<JsonProperty> properties = base.CreateProperties(type, memberSerialization);
// only serializer properties that are not named after the specified property.
properties =
properties.Where(p => string.Compare(p.PropertyName, _propertyNameToExclude, true) != 0).ToList();
return properties;
}
}
LINQ 可能不正确，我没有机会对此进行测试。然后您可以按如下方式使用它：
string json = JsonConvert.SerializeObject(car, Formatting.Indented,
new JsonSerializerSettings { ContractResolver = new DynamicContractResolver("LastModified") });
请参阅the documentation 了解更多信息。
【讨论】：
根据上面的@Underscore 帖子，我创建了一个要在序列化时排除的属性列表。
public class DynamicContractResolver : DefaultContractResolver {
private readonly string[] props;
public DynamicContractResolver(params string[] prop) {
this.props = prop;
}
protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization) {
IList<JsonProperty> retval = base.CreateProperties(type, memberSerialization);
// return all the properties which are not in the ignore list
retval = retval.Where(p => !this.props.Contains(p.PropertyName)).ToList();
return retval;
}
}
用途：
string json = JsonConvert.SerializeObject(car, Formatting.Indented,
new JsonSerializerSettings { ContractResolver = new DynamicContractResolver("ID", "CreatedAt", "LastModified") });
【讨论】：
通过引用Dynamically rename or ignore properties without changing the serialized class，我们可以在运行时实现JsonIgnore。这是一个可行的解决方案。
以 Person 类为例：
public class Person
{
// ignore property
[JsonIgnore]
public string Title { get; set; }
// rename property
[JsonProperty("firstName")]
public string FirstName { get; set; }
}
第 1 步：创建类“PropertyRenameAndIgnoreSerializerContractResolver”
public class PropertyRenameAndIgnoreSerializerContractResolver : DefaultContractResolver
{
private readonly Dictionary<Type, HashSet<string>> _ignores;
private readonly Dictionary<Type, Dictionary<string, string>> _renames;
public PropertyRenameAndIgnoreSerializerContractResolver()
{
_ignores = new Dictionary<Type, HashSet<string>>();
_renames = new Dictionary<Type, Dictionary<string, string>>();
}
public void IgnoreProperty(Type type, params string[] jsonPropertyNames)
{
if (!_ignores.ContainsKey(type))
_ignores[type] = new HashSet<string>();
foreach (var prop in jsonPropertyNames)
_ignores[type].Add(prop);
}
public void RenameProperty(Type type, string propertyName, string newJsonPropertyName)
{
if (!_renames.ContainsKey(type))
_renames[type] = new Dictionary<string, string>();
_renames[type][propertyName] = newJsonPropertyName;
}
protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
{
var property = base.CreateProperty(member, memberSerialization);
if (IsIgnored(property.DeclaringType, property.PropertyName))
{
property.ShouldSerialize = i => false;
property.Ignored = true;
}
if (IsRenamed(property.DeclaringType, property.PropertyName, out var newJsonPropertyName))
property.PropertyName = newJsonPropertyName;
return property;
}
private bool IsIgnored(Type type, string jsonPropertyName)
{
if (!_ignores.ContainsKey(type))
return false;
return _ignores[type].Contains(jsonPropertyName);
}
private bool IsRenamed(Type type, string jsonPropertyName, out string newJsonPropertyName)
{
Dictionary<string, string> renames;
if (!_renames.TryGetValue(type, out renames) || !renames.TryGetValue(jsonPropertyName, out newJsonPropertyName))
{
newJsonPropertyName = null;
return false;
}
return true;
}
}
第 2 步：在 Jsonignore 想要应用的方法中添加代码
var person = new Person();
var jsonResolver = new PropertyRenameAndIgnoreSerializerContractResolver();
jsonResolver.IgnoreProperty(typeof(Person), "Title");
jsonResolver.RenameProperty(typeof(Person), "FirstName", "firstName");
var serializerSettings = new JsonSerializerSettings();
serializerSettings.ContractResolver = jsonResolver;
var json = JsonConvert.SerializeObject(person, serializerSettings);
【讨论】：
试试这个：
public static void IgnoreProperty<T, TR>(this T parameter, Expression<Func<T, TR>> propertyLambda)
{
var parameterType = parameter.GetType();
var propertyName = propertyLambda.GetReturnedPropertyName();
if (propertyName == null)
{
return;
}
var jsonPropertyAttribute = parameterType.GetProperty(propertyName).GetCustomAttribute<JsonPropertyAttribute>();
jsonPropertyAttribute.DefaultValueHandling = DefaultValueHandling.Ignore;
}
public static string GetReturnedPropertyName<T, TR>(this Expression<Func<T, TR>> propertyLambda)
{
var member = propertyLambda.Body as MemberExpression;
var memberPropertyInfo = member?.Member as PropertyInfo;
return memberPropertyInfo?.Name;
}
所以你可以这样做：
carObject.IgnoreProperty(so => so.LastModified);
【讨论】：
JsonPropertyAttribute。在这种情况下，您不妨直接设置DefaultValueHandling 。如果没有，GetCustomAttribute() 会返回 null，并且您会在下一行得到 NullReferenceException。
根据接受的答案，它会是：
[JsonIgnore]
public bool JsonIgnore { get; set; }
public bool ImageModified { get; set; }
public bool ShouldSerializeImageModified() => !JsonIgnore;
只要将JsonIgnore 设置为true，就意味着ImageModified 不会被序列化，并且JsonIgnore 会因为[JsonIgnore] 而被忽略。
如果需要以这种方式编写代码，则可能表明设计不佳。系统中可能需要有 DTO 或 ViewModel，除非您想动态禁用/启用某些属性的序列化。
【讨论】：
关于所有正确答案，我想补充一点。当您有同名的嵌套属性时，忽略将影响所有同名的属性。如果您想忽略特定属性，可以执行以下操作：
public class DynamicContractResolver : DefaultContractResolver
{
private readonly string[] props;
public DynamicContractResolver(params string[] prop)
{
this.props = prop;
}
protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
{
IList<JsonProperty> retval = base.CreateProperties(type, memberSerialization);
return retval.Where(p => !this.props.Contains(p.DeclaringType.FullName + "." + p.PropertyName)).ToList();
}
}
那么当你想使用它的时候你可以说：
var values = await _dbContext
.Set<EntityName>()
.Where(...).ToList();
var json = JsonConvert.SerializeObject(values, Formatting.Indented,
new JsonSerializerSettings
{
ReferenceLoopHandling = ReferenceLoopHandling.Ignore,
ContractResolver = new DynamicContractResolver("Entities.Contact.Address1","Entities.User.Name","Entities.Event.Name")
});
Address1 将在 Contact 中被忽略，而不是在其他任何地方。
【讨论】：