在ASP.NET Core 中连接数据库需要以下步骤：

1. 安装数据库提供者包
   对于不同的数据库，需要安装相应的包：SQL Server: Microsoft.EntityFrameworkCore.SqlServerMySQL: Pomelo.EntityFrameworkCore.MySqlPostgreSQL: Npgsql.EntityFrameworkCore.PostgreSQLSQLite: Microsoft.EntityFrameworkCore.Sqlite
2. 配置连接字符串
   在appsettings.json中添加连接字符串：
3. json

{ "ConnectionStrings": { "DefaultConnection": "Server=(localdb)\\mssqllocaldb;Database=MyDatabase;Trusted_Connection=True;MultipleActiveResultSets=true" }, "Logging": { "LogLevel": { "Default": "Information", "Microsoft.AspNetCore": "Warning" } }, "AllowedHosts": "*" }

1. 
   
2. 定义数据模型
   创建表示数据库表的实体类：
3. csharp

public class Product { public int Id { get; set; } public string Name { get; set; } public decimal Price { get; set; } }

1. 
   
2. 创建数据库上下文
   继承DbContext并配置实体：
3. csharp

using Microsoft.EntityFrameworkCore; public class ApplicationDbContext : DbContext { public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) : base(options) { } public DbSet<Product> Products { get; set; } }

1. 
   
2. 注册数据库上下文
   在Program.cs中注册数据库上下文和连接字符串：
3. csharp

builder.Services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection")));

1. 
   
2. 使用依赖注入访问数据库
   在控制器中通过构造函数注入数据库上下文：
3. csharp

private readonly ApplicationDbContext _context; public ProductsController(ApplicationDbContext context) { _context = context; }

1. 
   
2. 执行数据库操作
   使用 DbContext 执行 CRUD 操作：
3. csharp

// 获取所有产品
 [HttpGet]
 public async Task<ActionResult<IEnumerable<Product>>> GetProducts() { return await _context.Products.ToListAsync(); } // 创建新产品 [HttpPost] public async Task<ActionResult<Product>> PostProduct(Product product) { _context.Products.Add(product); await _context.SaveChangesAsync(); return CreatedAtAction(nameof(GetProduct), new { id = product.Id }, product); }

完整示例代码

下面是一个完整的 SQL Server 数据库连接示例：

csharp

// Program.cs
using Microsoft.EntityFrameworkCore;

var builder = WebApplication.CreateBuilder(args);

// 添加数据库上下文
builder.Services.AddDbContext<ApplicationDbContext>(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection")));

// 添加控制器
builder.Services.AddControllers();

// 添加Swagger
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

var app = builder.Build();

// 配置开发环境使用Swagger
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();
app.UseAuthorization();
app.MapControllers();
app.Run();

// Models/Product.cs
public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }
}

// Data/ApplicationDbContext.cs
using Microsoft.EntityFrameworkCore;

public class ApplicationDbContext : DbContext
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options)
    {
    }

    public DbSet<Product> Products { get; set; }
}

// Controllers/ProductsController.cs
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;

[ApiController]
[Route("[controller]")]
public class ProductsController : ControllerBase
{
    private readonly ApplicationDbContext _context;

    public ProductsController(ApplicationDbContext context)
    {
        _context = context;
    }

    [HttpGet]
    public async Task<ActionResult<IEnumerable<Product>>> GetProducts()
    {
        return await _context.Products.ToListAsync();
    }

    [HttpGet("{id}")]
    public async Task<ActionResult<Product>> GetProduct(int id)
    {
        var product = await _context.Products.FindAsync(id);

        if (product == null)
        {
            return NotFound();
        }

        return product;
    }

    [HttpPost]
    public async Task<ActionResult<Product>> PostProduct(Product product)
    {
        _context.Products.Add(product);
        await _context.SaveChangesAsync();

        return CreatedAtAction(nameof(GetProduct), new { id = product.Id }, product);
    }
}

其他数据库连接示例

MySQL 连接

csharp

// Program.cs
builder.Services.AddDbContext<ApplicationDbContext>(options =>
    options.UseMySql(
        builder.Configuration.GetConnectionString("DefaultConnection"),
        ServerVersion.AutoDetect(builder.Configuration.GetConnectionString("DefaultConnection"))
    )
);

// appsettings.json
"ConnectionStrings": {
  "DefaultConnection": "server=localhost;user=root;password=yourpassword;database=mydatabase"
}

PostgreSQL 连接

csharp

// Program.cs
builder.Services.AddDbContext<ApplicationDbContext>(options =>
    options.UseNpgsql(builder.Configuration.GetConnectionString("DefaultConnection"))
);

// appsettings.json
"ConnectionStrings": {
  "DefaultConnection": "Host=localhost;Database=mydatabase;Username=postgres;Password=yourpassword"
}

SQLite 连接

csharp

// Program.cs
builder.Services.AddDbContext<ApplicationDbContext>(options =>
    options.UseSqlite(builder.Configuration.GetConnectionString("DefaultConnection"))
);

// appsettings.json
"ConnectionStrings": {
  "DefaultConnection": "Data Source=MyDatabase.db"
}

根据你的需求选择合适的数据库提供者，并相应地配置连接字符串和 DbContext。