ASP.NET Core 8 Web API从ClickHouse脚手架生成实体遇DesignTimeProviderServices错误

问题场景 #

在ASP.NET Core 8 Web API项目中尝试从ClickHouse数据库生成实体，已安装的NuGet包配置如下：

<ItemGroup>
    <PackageReference Include="ClickHouse.Client" Version="7.7.3" />
    <PackageReference Include="EFCore.ClickHouse" Version="8.0.0" />
    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="8.0.8" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="8.0.8">
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
      <PrivateAssets>all</PrivateAssets>
    </PackageReference>
    <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="8.0.8">
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
      <PrivateAssets>all</PrivateAssets>
    </PackageReference>
    <PackageReference Include="Swashbuckle.AspNetCore" Version="6.4.0" />
</ItemGroup>

执行EF Core脚手架命令：

dotnet ef dbcontext scaffold "Host=127.0.0.1;Port=8123;User=default;Password=;Database=db2;Compress=True;CheckCompressedHash=False;SocketTimeout=60000000;Compressor=lz4" EFCore.ClickHouse -o Models -c MyDbContext

触发错误提示：

Unable to find expected assembly attribute [DesignTimeProviderServices] in provider assembly 'EFCore.ClickHouse'. This attribute is required to identify the class which acts as the design-time service provider factory for the provider.

已确认连接字符串可正常访问ClickHouse数据库。

解决方法 #

1. 统一EF Core与EFCore.ClickHouse版本 #

EFCore.ClickHouse 8.0.0与EF Core 8.0.8存在版本适配问题，需将EF Core相关包降级至8.0.0，保持版本一致：

修改项目文件中的NuGet包配置：

<ItemGroup>
    <PackageReference Include="ClickHouse.Client" Version="7.7.3" />
    <PackageReference Include="EFCore.ClickHouse" Version="8.0.0" />
    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="8.0.0" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="8.0.0">
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
      <PrivateAssets>all</PrivateAssets>
    </PackageReference>
    <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="8.0.0">
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
      <PrivateAssets>all</PrivateAssets>
    </PackageReference>
    <PackageReference Include="Swashbuckle.AspNetCore" Version="6.4.0" />
</ItemGroup>

执行dotnet restore命令恢复包，之后重新运行脚手架命令。

2. 手动实现设计时DbContext工厂 #

若版本调整后问题仍存在，可手动创建设计时服务工厂类，绕过自动检测逻辑：

在项目中添加如下类：

using Microsoft.EntityFrameworkCore.Design;
using Microsoft.EntityFrameworkCore;
using EFCore.ClickHouse.Infrastructure;

public class ClickHouseDesignTimeFactory : IDesignTimeDbContextFactory<MyDbContext>
{
    public MyDbContext CreateDbContext(string[] args)
    {
        var optionsBuilder = new DbContextOptionsBuilder<MyDbContext>();
        optionsBuilder.UseClickHouse("Host=127.0.0.1;Port=8123;User=default;Password=;Database=db2;Compress=True;CheckCompressedHash=False;SocketTimeout=60000000;Compressor=lz4");

        return new MyDbContext(optionsBuilder.Options);
    }
}

确保MyDbContext类名称与脚手架命令中的-c MyDbContext参数一致，之后重新执行脚手架命令。

3. 备选方案：使用ClickHouse.Client手动生成实体 #

如果EFCore.ClickHouse的脚手架功能持续异常，可直接使用ClickHouse.Client查询表结构，手动或通过T4模板生成实体类：

• 编写代码连接ClickHouse，查询system.tables和system.columns获取表与字段信息
• 根据查询结果编写实体类，或借助T4模板实现自动化生成

内容的提问来源于stack exchange，提问作者navnforfun