C#运行报错CS8803，Azure Cosmos DB示例代码如何正确结构化？

错误CS8803的核心规则是：C#顶级语句（无类/方法包裹的直接执行代码）必须放在所有命名空间、类、record等类型声明的前面。你当前代码把Product这个record类型定义插在了顶级执行代码中间，违反了这个编译规则。

下面提供两种修正方案：

方案1：调整类型声明位置（推荐，保留顶级语句简洁风格） #

把Product record移到using语句之后、所有执行代码之前即可：

// See https://aka.ms/new-console-template for more information
using Microsoft.Azure.Cosmos;
using Azure.Identity;

// C# record representing an item in the container
public record Product(
    string id,
    string categoryId,
    string categoryName,
    string name,
    int quantity,
    bool sale
);

// New instance of CosmosClient class
using CosmosClient client = new(
    accountEndpoint: Environment.GetEnvironmentVariable("COSMOS_ENDPOINT"),
    tokenCredential: new DefaultAzureCredential()
);

// Database reference with creation if it does not already exist
Database database = client.GetDatabase(id: "cosmicworks");

Console.WriteLine("Hello, World!");

Console.WriteLine($"New database:\t{database.Id}");

// Container reference with creation if it does not already exist
Container container = database.GetContainer(id: "products");

Console.WriteLine($"New container:\t{container.Id}");

// Create new object and upsert (create or replace) to container
Product newItem = new(
    id: "70b63682-b93a-4c77-aad2-65501347265f",
    categoryId: "61dba35b-4f02-45c5-b648-c6badc0cbd79",
    categoryName: "gear-surf-surfboards",
    name: "Yamba Surfboard",
    quantity: 12,
    sale: false
);

Product createdItem = await container.CreateItemAsync<Product>(
    item: newItem
);

Console.WriteLine($"Created item:\t{createdItem.id}\t[{createdItem.categoryName}]");

// Point read item from container using the id and partitionKey
Product readItem = await container.ReadItemAsync<Product>(
    id: "70b63682-b93a-4c77-aad2-65501347265f",
    partitionKey: new PartitionKey("61dba35b-4f02-45c5-b648-c6badc0cbd79")
);

// Create query using a SQL string and parameters
var query = new QueryDefinition(
    query: "SELECT * FROM products p WHERE p.categoryId = @categoryId"
)
    .WithParameter("@categoryId", "61dba35b-4f02-45c5-b648-c6badc0cbd79");

using FeedIterator<Product> feed = container.GetItemQueryIterator<Product>(
    queryDefinition: query
);

while (feed.HasMoreResults)
{
    FeedResponse<Product> response = await feed.ReadNextAsync();
    foreach (Product item in response)
    {
        Console.WriteLine($"Found item:\t{item.name}");
    }
}

方案2：改用传统控制台程序结构（包裹在类和Main方法中） #

如果更习惯传统C#控制台的类+方法结构，可以把所有逻辑放到Program类的异步Main方法里：

using Microsoft.Azure.Cosmos;
using Azure.Identity;

// C# record representing an item in the container
public record Product(
    string id,
    string categoryId,
    string categoryName,
    string name,
    int quantity,
    bool sale
);

class Program
{
    static async Task Main(string[] args)
    {
        // New instance of CosmosClient class
        using CosmosClient client = new(
            accountEndpoint: Environment.GetEnvironmentVariable("COSMOS_ENDPOINT"),
            tokenCredential: new DefaultAzureCredential()
        );

        // Database reference with creation if it does not already exist
        Database database = client.GetDatabase(id: "cosmicworks");

        Console.WriteLine("Hello, World!");

        Console.WriteLine($"New database:\t{database.Id}");

        // Container reference with creation if it does not already exist
        Container container = database.GetContainer(id: "products");

        Console.WriteLine($"New container:\t{container.Id}");

        // Create new object and upsert (create or replace) to container
        Product newItem = new(
            id: "70b63682-b93a-4c77-aad2-65501347265f",
            categoryId: "61dba35b-4f02-45c5-b648-c6badc0cbd79",
            categoryName: "gear-surf-surfboards",
            name: "Yamba Surfboard",
            quantity: 12,
            sale: false
        );

        Product createdItem = await container.CreateItemAsync<Product>(
            item: newItem
        );

        Console.WriteLine($"Created item:\t{createdItem.id}\t[{createdItem.categoryName}]");

        // Point read item from container using the id and partitionKey
        Product readItem = await container.ReadItemAsync<Product>(
            id: "70b63682-b93a-4c77-aad2-65501347265f",
            partitionKey: new PartitionKey("61dba35b-4f02-45c5-b648-c6badc0cbd79")
        );

        // Create query using a SQL string and parameters
        var query = new QueryDefinition(
            query: "SELECT * FROM products p WHERE p.categoryId = @categoryId"
        )
            .WithParameter("@categoryId", "61dba35b-4f02-45c5-b648-c6badc0cbd79");

        using FeedIterator<Product> feed = container.GetItemQueryIterator<Product>(
            queryDefinition: query
        );

        while (feed.HasMoreResults)
        {
            FeedResponse<Product> response = await feed.ReadNextAsync();
            foreach (Product item in response)
            {
                Console.WriteLine($"Found item:\t{item.name}");
            }
        }
    }
}

两种方案都能解决编译错误：方案1更贴合.NET 6+的极简风格，只需调整代码位置；方案2适合熟悉传统C#结构的开发者。

内容的提问来源于stack exchange，提问作者Manu Chadha