.NET 6 ASP.NET应用调用AddElasticsearch扩展报编译错误如何解决

错误原因 #

你定义的AddElasticsearch扩展方法的第二个入参要求直接传入IConfiguration实例，但你调用时传入了lambda表达式，类型不匹配才触发编译报错。

修正方法 #

直接修改Program.cs里的调用代码，把lambda替换成builder.Configuration即可：

var builder = WebApplication.CreateBuilder(args);

builder.Services
    // 直接传入Configuration实例，不要用lambda
    .AddElasticsearch(builder.Configuration)
    .AddGraphQLServer()
    .AddQueryType<Query>();

var app = builder.Build();

app.MapGraphQL();

app.Run();

可选优化（支持lambda配置风格） #

如果你想要保留options => { }的配置写法，可以调整扩展方法的定义，改成支持选项委托的形式：

public static class Extensions
{
    // 新增支持选项委托的重载
    public static void AddElasticsearch(this IServiceCollection services, Action<ElasticsearchOptions> configureOptions)
    {
        var options = new ElasticsearchOptions();
        configureOptions(options);
        
        var settings = new ConnectionSettings(new Uri(options.Url)).DefaultIndex(options.DefaultIndex);
        AddDefaultMappings(settings);
        var client = new ElasticClient(settings);
        services.AddSingleton(client);
        CreateIndex<LegiscanModelBill>(client, options.DefaultIndex);
    }

    // 原有接收IConfiguration的重载也可以保留
    public static void AddElasticsearch(this IServiceCollection services, IConfiguration configuration)
    {
        var url = configuration["elasticsearch:url"];
        var defaultIndex = configuration["elasticsearch:index"];

        var settings = new ConnectionSettings(new Uri(url)).DefaultIndex(defaultIndex);

        AddDefaultMappings(settings);

        var client = new ElasticClient(settings);

        services.AddSingleton(client);

        CreateIndex<LegiscanModelBill>(client, defaultIndex);
    }

    private static void AddDefaultMappings(ConnectionSettings settings) => settings.DefaultMappingFor<LegiscanModelBill>(m => m);

    private static void CreateIndex<T>(ElasticClient client, string indexName) where T : class
    {
        // 建议把ToString()换成Name，避免索引名带上类的完整命名空间
        client.Indices.Create($"{indexName}_{typeof(T).Name}", i => i.Map<T>(m => m.AutoMap()));
    }
}

// 新增选项类
public class ElasticsearchOptions
{
    public string Url { get; set; }
    public string DefaultIndex { get; set; }
}

调整后你就可以用lambda写法传入配置了：

builder.Services.AddElasticsearch(options => 
{
    options.Url = builder.Configuration["elasticsearch:url"];
    options.DefaultIndex = builder.Configuration["elasticsearch:index"];
});

内容的提问来源于stack exchange，提问作者Antarr Byrd