如何添加元数据以描述JSON.Net中哪些属性是日期 [英] How to add metadata to describe which properties are dates in JSON.Net
问题描述
我想在我的json中添加一个元数据属性，以便客户端可以知道什么是日期.
I would like to add a metadata property to my json so that the client side can know what properties are dates.
例如，如果我有一个像这样的对象:
For example if I had an object like this:
{
"notADate": "a value",
"aDate": "2017-04-23T18:25:43.511Z",
"anotherDate": "2017-04-23T18:25:43.511Z"
}
我想添加一个元数据属性，以告知消费者将哪些属性视为日期，如下所示:
I would like to add a metadata property to tell the consumer which properties to treat as dates something like this:
{
"_date_properties_": ["aDate", "anotherDate"],
"notADate": "a value",
"aDate": "2017-04-23T18:25:43.511Z",
"anotherDate": "2017-04-23T18:25:43.511Z"
}
任何帮助都会很棒，谢谢！
Any help would be great, thanks!
推荐答案
您可以创建属性插入序列化的每个对象的协定中.
You could create a custom ContractResolver that inserts a synthetic "_date_properties_" property into the contract of every object that is serialized.
为此，请首先子类 DefaultContractResolver 由添加了应用程序的事件处理程序创建的合同可以流利地定制:
To do this, first subclass DefaultContractResolver to allow contracts to be fluently customized after they have been created by application-added event handlers:
public class ConfigurableContractResolver : DefaultContractResolver
{
readonly object contractCreatedPadlock = new object();
event EventHandler<ContractCreatedEventArgs> contractCreated;
int contractCount = 0;
void OnContractCreated(JsonContract contract, Type objectType)
{
EventHandler<ContractCreatedEventArgs> created;
lock (contractCreatedPadlock)
{
contractCount++;
created = contractCreated;
}
if (created != null)
{
created(this, new ContractCreatedEventArgs(contract, objectType));
}
}
public event EventHandler<ContractCreatedEventArgs> ContractCreated
{
add
{
lock (contractCreatedPadlock)
{
if (contractCount > 0)
{
throw new InvalidOperationException("ContractCreated events cannot be added after the first contract is generated.");
}
contractCreated += value;
}
}
remove
{
lock (contractCreatedPadlock)
{
if (contractCount > 0)
{
throw new InvalidOperationException("ContractCreated events cannot be removed after the first contract is generated.");
}
contractCreated -= value;
}
}
}
protected override JsonContract CreateContract(Type objectType)
{
var contract = base.CreateContract(objectType);
OnContractCreated(contract, objectType);
return contract;
}
}
public class ContractCreatedEventArgs : EventArgs
{
public JsonContract Contract { get; private set; }
public Type ObjectType { get; private set; }
public ContractCreatedEventArgs(JsonContract contract, Type objectType)
{
this.Contract = contract;
this.ObjectType = objectType;
}
}
public static class ConfigurableContractResolverExtensions
{
public static ConfigurableContractResolver Configure(this ConfigurableContractResolver resolver, EventHandler<ContractCreatedEventArgs> handler)
{
if (resolver == null || handler == null)
throw new ArgumentNullException();
resolver.ContractCreated += handler;
return resolver;
}
}
Next, create an extension method to add the desired property to a JsonObjectContract:
public static class JsonContractExtensions
{
const string DatePropertiesName = "_date_properties_";
public static void AddDateProperties(this JsonContract contract)
{
var objectContract = contract as JsonObjectContract;
if (objectContract == null)
return;
var properties = objectContract.Properties.Where(p => p.PropertyType == typeof(DateTime) || p.PropertyType == typeof(DateTime?)).ToList();
if (properties.Count > 0)
{
var property = new JsonProperty
{
DeclaringType = contract.UnderlyingType,
PropertyName = DatePropertiesName,
UnderlyingName = DatePropertiesName,
PropertyType = typeof(string[]),
ValueProvider = new FixedValueProvider(properties.Select(p => p.PropertyName).ToArray()),
AttributeProvider = new NoAttributeProvider(),
Readable = true,
Writable = false,
// Ensure // Ensure PreserveReferencesHandling and TypeNameHandling do not apply to the synthetic property.
ItemIsReference = false,
TypeNameHandling = TypeNameHandling.None,
};
objectContract.Properties.Insert(0, property);
}
}
class FixedValueProvider : IValueProvider
{
readonly object properties;
public FixedValueProvider(object value)
{
this.properties = value;
}
#region IValueProvider Members
public object GetValue(object target)
{
return properties;
}
public void SetValue(object target, object value)
{
throw new NotImplementedException("SetValue not implemented for fixed properties; set JsonProperty.Writable = false.");
}
#endregion
}
class NoAttributeProvider : IAttributeProvider
{
#region IAttributeProvider Members
public IList<Attribute> GetAttributes(Type attributeType, bool inherit) { return new Attribute[0]; }
public IList<Attribute> GetAttributes(bool inherit) { return new Attribute[0]; }
#endregion
}
}
最后，按如下所示序列化示例类型:
Finally, serialize your example type as follows:
var settings = new JsonSerializerSettings
{
ContractResolver = new ConfigurableContractResolver
{
// Here I am using CamelCaseNamingStrategy as is shown in your JSON.
// If you don't want camel case, leave NamingStrategy null.
NamingStrategy = new CamelCaseNamingStrategy(),
}.Configure((s, e) => { e.Contract.AddDateProperties(); }),
};
var json = JsonConvert.SerializeObject(example, Formatting.Indented, settings);
此解决方案仅处理静态类型的DateTime和DateTime?属性.如果您具有object值的属性，有时具有DateTime值，或者是Dictionary<string, DateTime>或包含DateTime值的扩展数据，您将需要一个更复杂的解决方案.
This solution only handles statically typed DateTime and DateTime? properties. If you have object-valued properties that sometimes have DateTime values, or a Dictionary<string, DateTime>, or extension data containing DateTime values, you will need a more complex solution.
(As an alternative implementation, you could instead subclass DefaultContractResolver.CreateObjectContract and hardcode the required properties there using JsonContractExtensions.AddDateProperties(), however I thought it would be more interesting to create a general-purpose, fluently configurable contract resolver in case it becomes necessary to plug in different customizations later.)
您可能想要缓存合同解析器以获得最佳性能.
You may want to cache the contract resolver for best performance.
示例 .Net小提琴.
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