Csharp Cosmos SDK和Newtonsoft对静态只读记录的可能Mutations

这是一个非常尴尬的错误，我花了一段时间才把它处理到这几行代码.完整的代码可以被抓取as fiddle，但你必须提供你的Cosmos URL和密钥才能运行.问题是，我们定义了一个public static readonly Author Unknown字段，而类Author是一个记录，其定义如下:

public record Author(
    [Required] string Id,
    [Required] string DisplayName,
    [Required] string MailAddress)
{
    // This is going to be mutated! 👇🏻
    public static readonly Author Unknown = Create(nameof(Unknown));

    public static Author Create(string name)
    {
        return new Author(
            name.ToLowerInvariant(),
            name,
            $"{name}@test.internal");
    }
}

在下一步中，我们有一个类，我们希望从/向Azure Cosmos数据库读取/写入，该类可以简单到

public class DocumentBase
{
    [Newtonsoft.Json.JsonProperty("id")]
    public Guid Id { get; set; } = default!;
    public string PartitionKey { get; set; } = "PartitionKey";

    // Apply static readonly record in default ctor of class
    public Author Modified { get; set; } = Author.Unknown;
}

我们设置中的下一件事是一个Cosmos DB容器，我们可以使用它来读/写我们的文档:

private static async Task<Container> CreateContainer()
{
    var endPoint = "https://{yourCosmosDatabase}.documents.azure.com:443/";
    var key = "{yourCosmosKey}";

    var client = new CosmosClient(endPoint, key);
    var containerId = $"{DateTime.UtcNow:s}-{Guid.NewGuid()}";
    var partitionKey = "/PartitionKey";

    var database = client.GetDatabase("Testing");
    var response = await database.CreateContainerAsync(new ContainerProperties
    {
        Id = containerId,
        PartitionKeyPath = partitionKey,
        DefaultTimeToLive = -1
    });

    return response.Container;
}

以下是更改Author.Unknown中的值的代码:

public static async Task Main()
{
    // Create a container to access Cosmos
    var container = await CreateContainer();

    // Create an instance with individual values
    var defaultValue = new DocumentBase
    {
        Id = Guid.NewGuid(),
        Modified = Author.Create("Modified"),
    };

    // Create a copy of the static readonly record for comparison
    var copyOfUnknown = Author.Unknown with { };
    // Check if the copy and the original values are equal
    // with value comparison thanks to the help of record
    Author.Unknown.ShouldBe(copyOfUnknown);

    // Let Cosmos write that instance down to the database
    // and read back the fresh created value.
    // It will be returned by the function, but we ignore it.
    await container.CreateItemAsync(defaultValue, new PartitionKey(defaultValue.PartitionKey));

    // Make another comparison that fails, because in Author.Unknown
    // you find now Author.Create("Modified")!
    Author.Unknown.ShouldBe(copyOfUnknown);
}

那么这里到底是怎么回事？ 我们有一个存储record的public static readonly字段，在对来自宇宙的响应进行反序列化后，那个字段发生了Mutations ？这怎么可能呢？

要解决这个问题，我们有多个选项，也许可以显示遇到这个问题所需的配料:

• 将readonly字段替换为属性getter，该属性getter在每次被调用时返回一个新实例.
• Do not set DocumentBase的默认ctor中的Modified属性
• Set使用复制ctor = Author.Unknown with { };在默认ctor DocumentBase中设置Modified属性

然而，这种行为确实出乎意料，如果有人能解释这种行为，我会很高兴.顺便说一下，我们使用了最新的NuGet软件包Microsoft.Azure.Cosmos 3.38.1.