.NET 6 WebAPI中HotelsSeeder实例创建失败，提示参数无法绑定

错误信息 #

System.InvalidOperationException: 'Cannot create instance of type 'Hotelum.HotelsSeeder' because one or more parameters cannot be bound to. Constructor parameters must have corresponding properties. Fields are not supported. Missing properties are: 'dbContext'

问题原因 #

你在Program.cs里调用了app.Configuration.Get<HotelsSeeder>();，这个方法是从配置文件（如appsettings.json）读取配置并绑定类实例，完全不依赖依赖注入(DI)容器。但HotelsSeeder的构造函数需要HotelsDbContext参数，配置文件里没有对应配置项，所以触发错误。而且你已经通过app.Services.GetRequiredService<HotelsSeeder>()从DI容器获取实例，这行代码完全多余。

另外GetHotels方法存在逻辑漏洞：你new了两个Hotels对象，但没有将它们添加到hotel列表中，导致Seed执行时不会向数据库插入任何数据。

解决方案 #

1. 移除错误的配置绑定代码 #

直接删掉Program.cs中的这一行：

app.Configuration.Get<HotelsSeeder>(); //Error appears

修改后的Program.cs关键代码：

var app = builder.Build();

// Configure the HTTP request pipeline.

HotelsSeeder seeder = app.Services.GetRequiredService<HotelsSeeder>(); 
seeder.Seed();

app.UseHttpsRedirection();
// ... 其他代码

2. 修复GetHotels方法的数据添加逻辑 #

在GetHotels方法中，把new出来的Hotels对象添加到hotel列表中：

修改后的GetHotels方法：

private IEnumerable<Hotels> GetHotels()
{
    var hotel = new List<Hotels>();
    // 添加第一个酒店
    hotel.Add(new Hotels()
    {
        Name = "Avocado",
        Description = "Perfect for family, chill and drinks",
        Category = "Holidays",
        IsItOpen = true,
        ContactEmail = "contact@avocado.com",
        ContactNumber = "123456789",
        Rooms = new List<Rooms>()
        {
            new Rooms()
            {
                Name = "Król",
                Description = "Dla bogatych",
                Price = 8549098M,
                NumberOfRooms = 1,
            },
            new Rooms()
            {
                Name = "Królowa",
                Description = "Dla mniej bogatych",
                Price = 89098M,
                NumberOfRooms = 5,
            },
            new Rooms()
            {
                Name = "Standart",
                Description = "Dla standartów",
                Price = 88M,
                NumberOfRooms = 25,
            },
        },
        Address = new Address()
        {
            City = "Wwa",
            Street = "Poznanska",
            PostalCode = "10-092"
        }
    });
    // 添加第二个酒店
    hotel.Add(new Hotels()
    {
        Name = "Abada",
        Description = "Perfect for horrors",
        Category = "Horros",
        IsItOpen = true,
        ContactEmail = "contact@abada.com",
        ContactNumber = "123456789",
        Rooms = new List<Rooms>
        {
            new Rooms()
            {
                Name = "Bieda",
                Description = "Dla odważnych",
                Price = 8M,
                NumberOfRooms = 1,
            },
            new Rooms()
            {
                Name = "Mniejsza bieda",
                Description = "Dla normalnych",
                Price = 98M,
                NumberOfRooms = 5,
            },
            new Rooms()
            {
                Name = "Bogato",
                Description = "Dla bogatych",
                Price = 88M,
                NumberOfRooms = 25,
            }
        },
        Address = new Address()
        {
            City = "Poznan",
            Street = "Warszawska",
            PostalCode = "50-792"
        }
    });
    return hotel;
}

额外说明 #

• 你已经正确将HotelsDbContext和HotelsSeeder注册到DI容器，通过app.Services.GetRequiredService<HotelsSeeder>()可以正常获取带有注入HotelsDbContext的实例。
• 确保HotelsDbContext配置正确，能正常连接数据库，否则Seed方法中的_dbContext.Database.CanConnect()会返回false，不会执行数据插入。

内容的提问来源于stack exchange，提问作者Insikt