System.Text.Json.JsonException：無法將 Json 轉換為 DataModel

Question

我正在嘗試從 json 文件將數據播種到數據庫中，但我一直遇到相同的錯誤。 如下所示的堆棧跟蹤。 我有一個 AppQuestion 類和一個 IncorrectAnswer 類。 數據旨在匹配這些模型並傳遞到我的數據庫中。 嘗試反序列化時，似乎 Seed Incorrect 數組導致了錯誤。 我更喜歡使用 System.Text.Json 而不是 Newsoft。 有沒有辦法處理數據並忠於我的模型。

種子數據.json：

[
{
  "Question": "Question1",
  "Incorrect": ["Answer1", "Answer2", "Answer3"],
  "Correct": "Answer4"
},
{
  "Question": "Question2",
  "Incorrect": ["Answer1", "Answer2", "Answer4"],
  "Correct": "Answer3"
}
]

C# 代碼

public class Seed
{
    public static async Task SeedQuestions(DataContext context)
    {
        if (await context.Questions.AnyAsync()) return;

        var questionData = await System.IO.File.ReadAllTextAsync("Data/QuestionSeedData.json");

        var questions = JsonSerializer.Deserialize<List<AppQuestion>>(questionData);
        foreach(var question in questions)
        {
            context.Questions.Add(question);
        }

        await context.SaveChangesAsync();
    }
}

public class AppQuestion
{
    
    public int Id { get; set; }
    public string Question { get; set; }
    public ICollection<IncorrectAnswer> Incorrect { get; set; }
    public string Correct { get; set; }
}


public class IncorrectAnswer
{
    public int Id { get; set; }

    public string Incorrect { get; set; }
    public AppQuestion AppQuestion { get; set; }

    public int AppQuestionId { get; set; }
}


public class DataContext : DbContext
{
    public DataContext( DbContextOptions options) : base(options)
    {
    }
    public DbSet<AppQuestion> Questions {get; set;}

    public DbSet<AppUser> Users { get; set; }
}
public class Program
{
    public static async Task Main(string[] args)
    {
        var host = CreateHostBuilder(args).Build();
        using var scope = host.Services.CreateScope();
        var services = scope.ServiceProvider;
        try
        {
            var context = services.GetRequiredService<DataContext>();
            await context.Database.MigrateAsync();
            await Seed.SeedQuestions(context);
        }
        catch (Exception ex)
        {
            var logger = services.GetRequiredService<ILogger<Program>>();
            logger.LogError(ex, "An error occurred during migration");
        }
        await host.RunAsync();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });
}

堆棧跟蹤：

fail: API.Program[0]
  An error occurred during migration
  System.Text.Json.JsonException: The JSON value could not be converted to API.Entities.IncorrectAnswer. Path: $[0].Incorrect[0] | LineNumber: 3 | BytePositionInLine: 28.
     at System.Text.Json.ThrowHelper.ThrowJsonException_DeserializeUnableToConvertValue(Type propertyType)
     at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
     at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
     at System.Text.Json.Serialization.Converters.IEnumerableDefaultConverter`2.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, TCollection& value)
     at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
     at System.Text.Json.JsonPropertyInfo`1.ReadJsonAndSetMember(Object obj, ReadStack& state, Utf8JsonReader& reader)
     at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
     at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
     at System.Text.Json.Serialization.Converters.IEnumerableDefaultConverter`2.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, TCollection& value)
     at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
     at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, JsonSerializerOptions options, ReadStack& state)
     at System.Text.Json.JsonSerializer.ReadCore[TValue](JsonConverter jsonConverter, Utf8JsonReader& reader, JsonSerializerOptions options, ReadStack& state)
     at System.Text.Json.JsonSerializer.ReadCore[TValue](Utf8JsonReader& reader, Type returnType, JsonSerializerOptions options)
     at System.Text.Json.JsonSerializer.Deserialize[TValue](String json, Type returnType, JsonSerializerOptions options)
     at System.Text.Json.JsonSerializer.Deserialize[TValue](String json, JsonSerializerOptions options)
     at API.Data.Seed.SeedQuestions(DataContext context) in C:\Users\fahua\Documents\TriviaTandem\API\Data\Seed.cs:line 20
     at API.Program.Main(String[] args) in C:\Users\fahua\Documents\TriviaTandem\API\Program.cs:line 26

Answer 1

AppQuestion類中的Incorrect屬性是IncorrectAnswer對象的集合，但在您的 json 中incorrect是字符串數組。

您需要更改模型或 json。

Answer 2

最后，我發現一個頁面提到在屬性中明確說明 DataMember。 我認為播種數據應該有一個更清晰的結果，但這目前有效。

public class Example
{
    [DataMember(Name="Question")]
    public string Question  { get; set; }

    [DataMember(Name="Incorrect")]
    public IList<string> Incorrect { get; set; }

    [DataMember(Name="Correct")]
    public string Correct { get; set; }
}


public class Seed
{
    public Seed()
    {
    }

    public static async Task SeedQuestions(DataContext context)
    {
        if (await context.Questions.AnyAsync()) return;

        var questionData = await System.IO.File.ReadAllTextAsync("Data/QuestionSeedData.json");

        var myDeserializedClass = JsonSerializer.Deserialize<List<Example>>(questionData);
        

        foreach (var item in myDeserializedClass)
        {
            var appQuestion = new AppQuestion();
            var incorrectAnswerList = new List<IncorrectAnswer>();

            appQuestion.Question = item.Question;
            appQuestion.Correct = item.Correct;
            foreach (var thing in item.Incorrect)
            {
                var incorrectAnswer = new IncorrectAnswer();
                incorrectAnswer.Incorrect = thing;
                incorrectAnswerList.Add(incorrectAnswer);
            }
            appQuestion.Incorrect = incorrectAnswerList;

            context.Questions.Add(appQuestion);
        }
        await context.SaveChangesAsync();
    }
}