如何使用EF核心从相关表中获取数据？

Question

我正在从事网络项目，我使用代码优先方法在机器模型和实验模型之间创建了一对多关系。 这是代码：

   public class Experiment
{

    public int Id { get; set; }
    public string Name { get; set; }
    public DateTime CreationDateTime { get; set; }
    public string Path { get; set; }
    public string Description { get; set; }

    [ForeignKey("Machine")]
    public int MachineId { get; set; }
    public Machine Machine { get; set; }
}


 public class Machine
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Type { get; set; }
    public string Description { get; set; }

    public ICollection<Experiment> Experiments { get; set; }
}

我可以通过 userId 过滤所有的实验：

  public async Task<IList<Experiment>> GetExperimentsAsync(int userId)
    {
        var experiments = await _experimentsDbContext.Experiments
                                .Where(x => x.UserId == userId)
                                .ToListAsync();

        return experiments; 
    }

但是我收到machine = null，我需要做的是按userId过滤实验列表并包含相关的机器对象，但我不能这样做。

Answer 1

您需要使用 .Include() 方法明确指定要加载相关数据。

请查看MS 文档

例子：

public async Task<IList<Experiment>> GetExperimentsAsync(int userId)
{
    var experiments = await _experimentsDbContext.Experiments
                            .Where(x => x.UserId == userId)
                            .Include(e => e.Machine)
                            .ToListAsync();

    return experiments; 
}

Answer 2

试试下面的代码：

public async Task<IList<Experiment>> GetExperimentsAsync(int userId)
{
    var experiments = await _experimentsDbContext.Experiments
                            .Include(experiment => experiment.Machine)
                            .Where(x => x.UserId == userId)
                            .ToListAsync();
    return experiments; 
}