NetCore 统一处理 webapi 返回null 转为“”

显示全部楼层 · 2019-9-26 09:21:07

数据库中部门表字段允许空值，则代码中实体类对应的字段类型为可空类型Nullable<>，如int?，DateTime?，null值字段序列化返回的值都为null，前端对应字段赋值必要做null值判断，随想到全局把null替换为""

网上找的方案都是重写了DefaultContractResolver，但是该方法只能办理string类型null→""的题目，对其他可空类型无效。

研究了下git 上Newtonsoft.Json和.netcore MVC的源码

终极利用自界说JsonOutputFormatter方式实现：

public class MyJsonOutputFormatter : JsonOutputFormatter
{
public MyJsonOutputFormatter(JsonSerializerSettings serializerSettings) : base(serializerSettings, ArrayPool<char>.Shared)
{
}
public new JsonSerializerSettings SerializerSettings => base.SerializerSettings;
protected override JsonWriter CreateJsonWriter(TextWriter writer)
{
if (writer == null)
{
throw new ArgumentNullException(nameof(writer));
}
var jsonWriter = new NullJsonWriter(writer)
{
ArrayPool = new JsonArrayPool<char>(ArrayPool<char>.Shared),
CloseOutput = false,
AutoCompleteOnClose = false
};
return jsonWriter;
}
}
public class NullJsonWriter : JsonTextWriter
{
public NullJsonWriter(TextWriter textWriter):base(textWriter)
{
}
public override void WriteNull()
{
this.WriteValue(String.Empty);
}
}

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在 Startup 代码里面修改

//services.AddMvc().AddJsonOptions(option => {
// //配置大小写题目，默认是首字母小写,该配置根据项目必要更改
// //option.SerializerSettings.ContractResolver = new Newtonsoft.Json.Serialization.DefaultContractResolver();
// //配置序列化时时间格式为时间戳
// //option.SerializerSettings.ContractResolver = new NullToEmptyStringResolver();
// option.SerializerSettings.DateFormatString = "yyyy-MM-dd HH:mm:ss";
//});
services.AddMvc(config =>
{
var settings = new JsonSerializerSettings();
//设置首字母小写，如果不必要则改为 DefaultContractResolver
settings.ContractResolver = new CamelCasePropertyNamesContractResolver();
//同一设置JsonResult中的日期格式
settings.DateFormatString = "yyyy-MM-dd HH:mm:ss";
config.OutputFormatters.Insert(0, new MyJsonOutputFormatter(settings));
});

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