1. 首先，需要在你的API控制器中注入以下服务：

private readonly UserManager _userManager;
private readonly ApplicationDbContext _dbContext;

public MandateController(UserManager userManager, ApplicationDbContext dbContext)
{
    _userManager = userManager;
    _dbContext = dbContext;
}

2. 在你的API操作中获取当前登录用户的ID：

var loggedInUserId = User.FindFirstValue(ClaimTypes.NameIdentifier);

3. 使用loggedInUserId从数据库中获取托管记录：

var mandateRecord = await _dbContext.Mandates.FirstOrDefaultAsync(x => x.UserId == loggedInUserId);

4. 完整代码示例：

[Authorize]
[ApiController]
[Route("[controller]")]
public class MandateController : ControllerBase
{
    private readonly UserManager _userManager;
    private readonly ApplicationDbContext _dbContext;

    public MandateController(UserManager userManager, ApplicationDbContext dbContext)
    {
        _userManager = userManager;
        _dbContext = dbContext;
    }

    [HttpGet("current")]
    public async Task> GetCurrentMandate()
    {
        var loggedInUserId = User.FindFirstValue(ClaimTypes.NameIdentifier);

        var mandateRecord = await _dbContext.Mandates.FirstOrDefaultAsync(x => x.UserId == loggedInUserId);

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

        return Ok(mandateRecord);
    }
}