ASP.NET Core 最小 API - 无法推断一个或多个参数

Posted 2023-03-27

【中文标题】ASP.NET Core 最小 API - 无法推断一个或多个参数

【英文标题】：ASP.NET Core minimal API - Failure to infer one or more parameters

【发布时间】：2022-01-05 04:26:09

【问题描述】：

我在 Microsoft 文档上关注 this tutorial 以创建一个最小的 API，我在 Visual Studio 上遇到了这个错误：

System.InvalidOperationException : 'Failure to infer one or more parameters.

这里是我正在使用的代码：

using Microsoft.EntityFrameworkCore;
var builder = WebApplication.CreateBuilder(args);

// Add services to the container.

var app = builder.Build();

// Configure the HTTP request pipeline.

 app.UseHttpsRedirection();

 app.MapGet("/", () => "Hello world !");

 // CREATE NEW ITEM /INVENTORY/ITEM
 app.MapPost("/inventory/item", async (Product product, ProductsDb db) =>
 
 db.Products.Add(product);
 await db.SaveChangesAsync();

  return Results.Created($"/inventory/product.Barcode", product);
  );


  // DELETE ITEM /ITEM
 app.MapDelete("/item/bc", async (int bc, ProductsDb db) =>
 
if (await db.Products.FindAsync(bc) is Product product)

    db.Products.Remove(product);
    await db.SaveChangesAsync();
    return Results.Ok(product);
 

return Results.NotFound();
);


// UPDATE ITEM /INVENTORY/item/barecode
app.MapPut("/inventory/item/bc", async (int bc, Product inputProduct, ProductsDb db) 
=>

var product = await db.Products.FindAsync(bc);

if (product is null) return Results.NotFound();

product.Name = inputProduct.Name;
product.Category = inputProduct.Category;
product.Price = inputProduct.Price;
product.Discount = inputProduct.Discount;
product.Quantity = inputProduct.Quantity;

await db.SaveChangesAsync();

return Results.NoContent();
);


// GET AL ITEMS  /INVENTORY/ITEMS
app.MapGet("/inventory/item", async (ProductsDb db) =>
await db.Products.ToListAsync());


// GET AL ITEMS  /INVENTORY/ITEMS/query?category=category
app.MapGet("/inventory/items/query?category=category", async (int bc, ProductsDb db) 
=>
await db.Products.FindAsync(bc)
    is Product product
        ? Results.Ok(product)
        : Results.NotFound());

 // GET AL ITEMS SORTED IN DESCENDING /INVENTORY/ITEM/SORT
app.MapGet("/inventory/item/sort", async (ProductsDb db) =>
await db.Products.OrderBy(p =>p.Price).ToListAsync());
app.Run();

class Product

public string Name  get; set; 
public string Category  get; set; 
public int Price  get; set; 
public int Discount  get; set; 
public int Quantity  get; set; 
public int Barcode  get; set; 
 

class ProductsDb : DbContext

public ProductsDb(DbContextOptions<ProductsDb> options)
    : base(options)  

public DbSet<Product> Products => Set<Product>();

我要做的是提供一些 API 端点，可以在数据库中获取或发布一些产品（实体框架代码优先）

我像教程一样使用 EntityFramework.InMemory，但我不知道它为什么会产生这个错误，我做错了什么吗？谢谢！

【参考方案1】：

首先，您需要在构建器之后添加上下文。

using Microsoft.EntityFrameworkCore;

var builder = WebApplication.CreateBuilder(args);

// Add these two lines
builder.Services.AddDbContext<ProductsDb>(opt => opt.UseInMemoryDatabase("ProductsList"));
builder.Services.AddDatabaseDeveloperPageExceptionFilter();

接下来，您必须按如下方式更正此方法：

// GET AL ITEMS /inventory/items/category/barecode
app.MapGet("/inventory/items/category/bc", async (int bc, ProductsDb db) 
// ...

最后，您必须在实体字符串中设置可为空值或默认值，以避免可空引用错误。

public string? Name  get; set; 
public string? Category  get; set; 

// OR
// public string Name  get; set;  = "default name";
// public string Category  get; set;  = "default category";