嵌套JSON转C# Model反序列化失败问题求助

错误信息 #

无法将当前JSON对象（例如{"name":"value"}）反序列化为类型'System.Collections.Generic.List`1[convert_json_to_model.Fields]'，因为该类型需要JSON数组（例如[1,2,3]）才能正确反序列化。
要修复此错误，请将JSON修改为JSON数组，或者修改反序列化类型为可从JSON对象反序列化的常规.NET类型（例如不是整数等基元类型，也不是数组或List等集合类型）。也可以为类型添加JsonObjectAttribute以强制其从JSON对象反序列化。
路径'nhits'，第1行，位置9。

部分JSON数据 #

{"nhits":17933,"parameters":{"dataset":["osm-fr-bars@babel"],"rows":3,"start":0,"format":"json","timezone":"UTC"},"records":[{"datasetid":"osm-fr-bars@babel","recordid":"d95394fd7d34aa34aa9b236661bce9cda534a8ab","fields":{"other_tags":"{\"cuisine\": \"tapas\", \"ref:FR:CRTA\": \"RESAQU047V506W6V\", \"capacity\": \"14\", \"description\": \"Tous les jours \u00e0 partir de 7h\", \"source\": \"BDOrtho IGN; Cadastre M\u00e0J 2015; Sirtaqui\", \"outdoor_seating\": \"yes\", \"source:ref:FR:CRTA\": \"Sirtaqui\"}","name":"Au boin coin","geo_point_2d":[44.0549704,0.2603921],"phone":"+33 5 53 65 67 45"},"geometry":{"type":"Point","coordinates":[0.2603921,44.0549704]}}]}

生成的C#模型代码 #

public class Fields
{
    [JsonProperty("other_tags")]
    public string OtherTags { get; set; }

    [JsonProperty("name")]
    public string Name { get; set; }

    [JsonProperty("geo_point_2d")]
    public List<double> GeoPoint2d { get; set; }

    [JsonProperty("phone")]
    public string Phone { get; set; }
}

public class Geometry
{
    [JsonProperty("type")]
    public string Type { get; set; }

    [JsonProperty("coordinates")]
    public List<double> Coordinates { get; set; }
}

public class Record
{
    [JsonProperty("datasetid")]
    public string Datasetid { get; set; }

    [JsonProperty("recordid")]
    public string Recordid { get; set; }

    [JsonProperty("fields")]
    public Fields Fields { get; set; }

    [JsonProperty("geometry")]
    public Geometry Geometry { get; set; }
}

public class Root
{
    [JsonProperty("records")]
    public List<Record> Records { get; set; }
}

出错的反序列化代码 #

static async Task Main(string[] args)
{
    string url = "https://data.opendatasoft.com/api/records/1.0/search/?dataset=osm-fr-bars%40babel&rows=30";
    HttpClient httpClient = new HttpClient();
    try
    {
        var httpResponseMessage = await httpClient.GetAsync(url); 
        string jsonResponse = await httpResponseMessage.Content.ReadAsStringAsync();
        List<Fields> myBars = JsonConvert.DeserializeObject<List<Fields>>(jsonResponse);
        foreach (var bar in myBars)
        {
            Console.WriteLine($"{bar.Name}");
        }
    }
    catch(Exception ex)
    {
        Console.WriteLine(ex.Message);
    }
}

解决方案 #

问题核心是：你试图把整个JSON对象直接反序列化为List<Fields>类型，但实际返回的JSON根节点是一个包含nhits、parameters、records的顶层对象，Fields集合嵌套在records数组的每一项里。

修改反序列化逻辑，先将JSON反序列化为Root类型，再从Root.Records中提取Fields：

static async Task Main(string[] args)
{
    string url = "https://data.opendatasoft.com/api/records/1.0/search/?dataset=osm-fr-bars%40babel&rows=30";
    HttpClient httpClient = new HttpClient();
    try
    {
        var httpResponseMessage = await httpClient.GetAsync(url); 
        string jsonResponse = await httpResponseMessage.Content.ReadAsStringAsync();
        // 先反序列化为Root类型
        Root root = JsonConvert.DeserializeObject<Root>(jsonResponse);
        // 提取所有Records中的Fields
        List<Fields> myBars = root.Records.Select(r => r.Fields).ToList();
        foreach (var bar in myBars)
        {
            Console.WriteLine($"{bar.Name}");
        }
    }
    catch(Exception ex)
    {
        Console.WriteLine(ex.Message);
    }
}

额外说明：如果需要使用nhits或parameters的数据，可以给Root类补充对应的属性：

public class Root
{
    [JsonProperty("nhits")]
    public int Nhits { get; set; }

    [JsonProperty("parameters")]
    public Parameters Parameters { get; set; }

    [JsonProperty("records")]
    public List<Record> Records { get; set; }
}

public class Parameters
{
    [JsonProperty("dataset")]
    public List<string> Dataset { get; set; }

    [JsonProperty("rows")]
    public int Rows { get; set; }

    [JsonProperty("start")]
    public int Start { get; set; }

    [JsonProperty("format")]
    public string Format { get; set; }

    [JsonProperty("timezone")]
    public string Timezone { get; set; }
}

内容的提问来源于stack exchange，提问作者saad moujid