ASP.NET Core 6中dbContext.Database.EnsureCreated()的正确放置位置

相关技术方案适用于早期版本的ASP.NET。使用Add-Migration InitialCreate和Update-Database命令可正确创建数据库，但无法实现应用启动时自动创建数据库，运行时出现错误提示。

相关代码 #

DotNet.P001.L07.MainProject > Program.cs

using DotNet.P001.L14.Database;
using Microsoft.EntityFrameworkCore;

namespace DotNet.P001.L07.MainProject;

public class Program
{
    public static void Main(string[] args)
    {
        var AngularCorsPolicy = "_angularCorsPolicy";

        var builder = WebApplication.CreateBuilder(args);

        builder.Services.AddDbContext<ApplicationDbContext>(option =>
           option.UseSqlServer(
            builder.Configuration.GetConnectionString("ApplicationContext")
            ?? throw new InvalidOperationException("Connection string 'ApplicationContext' not found.")));

        builder.Services.AddCors(options =>
        {
            options.AddPolicy(AngularCorsPolicy, policy =>
            {
                policy.WithOrigins(
                    "https://localhost:44472",
                     "https://localhost:7218"
                    )
                .AllowAnyHeader(); ;
            });
        });

        // Add services to the container.
        builder.Services.AddControllersWithViews();

        var app = builder.Build();
        
        // Create database if it does not exist
        ApplicationDbContext dbContext = app.Services.GetRequiredService<ApplicationDbContext>();
        dbContext.Database.EnsureCreated();

        // Configure the HTTP request pipeline.
        if(!app.Environment.IsDevelopment())
        {
            // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
            app.UseHsts();
        }

        app.UseHttpsRedirection();
        app.UseStaticFiles();
        app.UseRouting();
        app.UseCors(AngularCorsPolicy);

        app.MapControllerRoute(
            name: "default",
            pattern: "{controller}/{action=Index}/{id?}");

        app.MapFallbackToFile("index.html");

        app.Run();
    }
}

DotNet.P001.L14.Database > ApplicationDbContext.cs

using DotNet.P001.L14.Database.Entities;
using Microsoft.EntityFrameworkCore;

namespace DotNet.P001.L14.Database;
public class ApplicationDbContext : DbContext
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) : base(options)
    {
    }
    public DbSet<MessageEntity>? Message { get; set; }
}

DotNet.P001.L14.Database > Entities > MessageEntity.cs

namespace DotNet.P001.L14.Database.Entities;

public class MessageEntity
{
    public int Id { get; set; }
    public string? Content { get; set; }
    public string? FirstNameAuthor { get; set; }
    public string? LastNameAuthor { get; set; }
}

经排查，原有代码存在问题，需将以下代码片段：

ApplicationDbContext dbContext = app.Services.GetRequiredService<ApplicationDbContext>();
dbContext.Database.EnsureCreated();

替换为：

using(var scope = app.Services.CreateScope())
{
    var dbContext = scope.ServiceProvider.GetRequiredService<ApplicationDbContext>();
    
    // EnsureDeleted() 是可选操作，会先删除已存在的数据库
    dbContext.Database.EnsureDeleted(); 
    dbContext.Database.EnsureCreated();
}

该方案参考微软官方文档《运行时应用迁移》的内容。

内容的提问来源于stack exchange，提问作者kzstack