EF框架常见异常处理汇总

同一个实体被多次tracked的问题

错误提示 The instance of entity type ‘XXXX’ cannot be tracked because another instance with the same key value for {‘Key’} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached. 这里面的"XXXX"可能是任意一个实体模型的名称，“Key"则是这个实体的Key字段。出现这个错误的原因是试图更新某个实体时，拥有相同Key的另一个实体也被EF Core tracked了。常见以下情况：

Json字符串转换的对象赋值时

1. 定义一个Json字符串对象

public class Root
 {
     /// <summary>
     /// 
     /// </summary>
     public Signal signal { get; set; }
     /// <summary>
     /// 
     /// </summary>
     public Info info { get; set; }
     /// <summary>
     /// 
     /// </summary>
     public List<ListItem> list { get; set; } = new List<ListItem>();
 }

2. 赋值

//异常写法
Info  p_info= new  Info();
p_info.value1="1";
root.info = p_info;//赋值1
Signal p_signal=new  Signal();
p_signal.value1="测试"；
root.signal = p_signal; //赋值2
string message = JsonConvert.SerializeObject(root);  //转成Json字符串
//完成字符串发送后更新对应对象数据时提示异常

//正常写法  创建新对象赋值，避免引用类型指向同一个地址
root.info = p_info.ToJson().JsonToObject<TDataModel.Info>(); //赋值1
root.signal = signal.ToJson().JsonToObject<TDataModel.Signal>(); //赋值2
string message = JsonConvert.SerializeObject(root);

 public static class JsonHelper
 {
		public static string ToJson(this object obj)
{
    return JsonConvert.SerializeObject(obj);
}
    /// <summary>
    /// JSON格式转换为对象
    /// </summary>
    /// <param name="obj"></param>
    /// <returns></returns>
    public static T JsonToObject<T>(this string serialize) where T : class, new()
    {
        try
        {
            T deserialize = JsonConvert.DeserializeObject<T>(serialize);
            return deserialize;
        }
        catch (Exception e)
        {
            throw new Exception($"JsonToObject 异常：{e}");
        }
    }
}

持续更新中。。。。