.NET 9 Blazor连接MySQL时无法创建DbContext求助

尝试用.NET 9 Blazor连接MySQL 8.4.3数据库，查阅资料并尝试多种包后仍未成功，执行迁移命令时出现错误。

已安装的NuGet包 #

<ItemGroup>
    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="9.0.0" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="9.0.0">
        <PrivateAssets>all</PrivateAssets>
        <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
    </PackageReference>
    <PackageReference Include="Microsoft.EntityFrameworkCore.Relational" Version="9.0.0" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="9.0.0" />
    <PackageReference Include="Pomelo.EntityFrameworkCore.MySql" Version="8.0.2" />
</ItemGroup>

appsettings.json 配置 #

"ConnectionStrings": {
    "DefaultConnection": "Server=x.x.x.x;Database=DB_Cours;User=UserCours;Password=12345678"
},

Program.cs 配置代码 #

var connectionString = builder.Configuration.GetConnectionString("DefaultConnection") ?? throw new InvalidOperationException("Connection string 'DefaultConnection' not found.");

builder.Services.AddDbContext<MySqlDbContext>(options =>
    options.UseMySql(connectionString, new MySqlServerVersion(new Version(8,4,3))));
builder.Services.AddDatabaseDeveloperPageExceptionFilter();

MySqlDbContext 代码 #

public class MySqlDbContext(DbContextOptions<MySqlDbContext> options) : DbContext(options)
{
    public DbSet<Person>? Person { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        modelBuilder.Entity<Person>().HasData(
            new Person { Id = 1, Name = "Laurent"},
            new Person { Id = 2, Name = "John"},
            new Person { Id = 3, Name = "Mike" },
            new Person { Id = 4, Name = "Larry" }
        );
    }
}

执行迁移时的错误信息 #

Unable to create a 'DbContext' of type 'RuntimeType'.

The exception 'Method 'get_LockReleaseBehavior' in type 'Pomelo.EntityFrameworkCore.MySql.Migrations.Internal.MySqlHistoryRepository' from assembly 'Pomelo.EntityFrameworkCore.MySql, Version=8.0.2.0, Culture=neutral, PublicKeyToken=2cc498582444921b' does not have an implementation.' was thrown while attempting to create an instance.

解决方案 #

问题根源 #

错误是因为Pomelo.EntityFrameworkCore.MySql 8.0.2 不兼容 EF Core 9.0（.NET 9），EF Core 9新增了LockReleaseBehavior属性，旧版本Pomelo未实现该方法。

修复步骤 #

1. 卸载当前的Pomelo包：

   Uninstall-Package Pomelo.EntityFrameworkCore.MySql
   

2. 安装兼容EF Core 9的Pomelo版本（需与EF Core版本匹配）：

   Install-Package Pomelo.EntityFrameworkCore.MySql -Version 9.0.0
   

3. 确保所有EF Core相关包版本统一为9.0.0（当前配置已满足）
4. 重新执行迁移命令：

   Add-Migration Init
   

额外建议 #

MySQL 8.0+默认要求SSL连接，可在连接字符串中添加SslMode=Required避免连接失败：

"DefaultConnection": "Server=x.x.x.x;Database=DB_Cours;User=UserCours;Password=12345678;SslMode=Required"

内容的提问来源于stack exchange，提问作者JBD