Unable to create an object of type 'DbContext'. For the different patterns supported at design time

电脑版发表于：2022/5/5 12:27

如果在做EFCore migration时碰到如下错误：Unable to create an object of type 'DbContext'. For the different patterns supported at design time

**可尝试以下步骤进行处理：**

1：检查是否未实现EFContext默认构造函数
2：尝试清理解决方案，清除目录下的bin和obj
3：如果还不行，尝试在DbContext同级目录下添加类DesignTimeDbContextFactory
也就是自己写点逻辑执行以下执行迁移命令的逻辑
```
/* This class is needed for EF Core console commands
    * (like Add-Migration and Update-Database commands) */
public class WyJBLandDbContextFactory : IDesignTimeDbContextFactory<WyJBLandDbContext>
{
    public WyJBLandDbContext CreateDbContext(string[] args)
    {
        //BookStoreEfCoreEntityExtensionMappings.Configure();
        var configuration = BuildConfiguration();

        string conn = configuration.GetConnectionString("conn_mysql");

        AddTestLog(conn);

        var builder = new DbContextOptionsBuilder<WyJBLandDbContext>()
            .UseMySql(conn,ServerVersion.AutoDetect(conn));

        return new WyJBLandDbContext(builder.Options);
    }

    /// <summary>
    /// 记录一点内容用于测试
    /// </summary>
    /// <param name="content"></param>
    public void AddTestLog(string content) 
    {
        using (FileStream filestraem = new FileStream("d:/log.txt", FileMode.Append))
        {
            using (StreamWriter write = new StreamWriter(filestraem))
            {
                write.WriteLine(content);
                write.WriteLine("记录时间：" + DateTime.Now.ToString());
                write.WriteLine("----------------------------------------");
                write.Flush();
            }
        }
    }

    private static IConfigurationRoot BuildConfiguration()
    {
        var builder = new ConfigurationBuilder()
            .SetBasePath(Path.Combine(Directory.GetCurrentDirectory(), "../WY.JBLand.API/"))
            .AddJsonFile("appsettings.json", optional: true);

        return builder.Build();
    }
}
```

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Unable to create an object of type 'DbContext'. For the different patterns supported at design time

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