StringOrFirstArrayItemJsonConverter.cs
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using System.Text.Json;
using System.Text.Json.Serialization;
namespace FoodLabeling.Application.Contracts.Json;
/// <summary>
/// 反序列化时兼容 JSON 字符串或字符串数组（取首个非空元素），用于前端误把单选字段传成数组的场景（如 <c>partnerId</c>）。
/// </summary>
public sealed class StringOrFirstArrayItemJsonConverter : JsonConverter<string?>
{
public override string? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
{
switch (reader.TokenType)
{
case JsonTokenType.Null:
return null;
case JsonTokenType.String:
return reader.GetString();
case JsonTokenType.StartArray:
{
string? first = null;
while (reader.Read())
{
if (reader.TokenType == JsonTokenType.EndArray)
{
break;
}
if (reader.TokenType == JsonTokenType.Null)
{
continue;
}
if (reader.TokenType != JsonTokenType.String)
{
throw new JsonException("partnerId 数组元素必须是字符串");
}
var item = reader.GetString()?.Trim();
if (first is null && !string.IsNullOrWhiteSpace(item))
{
first = item;
}
}
return first;
}
default:
throw new JsonException($"无法将 JSON token {reader.TokenType} 转为字符串（partnerId）");
}
}
public override void Write(Utf8JsonWriter writer, string? value, JsonSerializerOptions options)
{
if (value is null)
{
writer.WriteNullValue();
}
else
{
writer.WriteStringValue(value);
}
}
}