Question

美好的一天

我正在使用ASP。带有C＃和实体框架的NET MVC。我的代码优先模型中有三个表。

public class Project
{
    public Guid Id { get; set; }
    public guid ProjectTypeId{ get; set; }
    public string projectType{ get; set; }
    [Required]
    public DateTime CreationDate{ get; set; }
    //more properties here
    //...
    public bool Activated{ get; set; }
    public IList<ProjectDetail> ProjectDetails{ get; set; }
}

您会看到一个项目有很多细节。

public class ProjectDetail
{
    [Required]
    public Guid Id { get; set; }
    public Project Project{ get; set; }
    [Required]
    public Guid ProjectId{ get; set; }             
    public string DetailDescription{ get; set; }
    public IList<ProjectDetailsAnswer> ProjectDetailsAnswers{ get; set; }
}

一个projectDetail有很多答案：

public class ProjectDetailsAnswer
{
    [Required]
    public Guid Id { get; set; }
    [Required]
    public Guid ProjectDetailId{ get; set; }
    public ProjectDetail ProjectDetail{ get; set; }       
    public string OtherField{ get; set; }
    [Required]
    [MaxLength(512)]
    public string AnswerDescription{ get; set; }
}

我想做的是使用带有lambda表达式的实体框架来加载视图模型

public class MyViewModel
{
    public Guid projectTypeId{ get; set; }
    public string projectType { get; set; }
    public string DetailDescription { get; set; }
    public IEnumerable<string> AnswerDescription{ get; set; }//this propertie comes from ProjectDetailsAnswer.AnswerDescription
}

到目前为止，我的代码是：

var y = _dbContext.Project
    .Include(a => a.ProjectDetail.Select(p => p.ProjectDetailsAnswer))
    .Select(n =>new MyViewModel{projectTypeId=n.projectTypeId,projectType =n.Project.projectType,DetailDescription =n.AnswerDescription.Select(b =>b.AnswerDescription).ToList()})
    .ToList();

我收到此错误：>无法在此代码中将字符串转换为List。 n.AnswerDescription.Select(b =>b.AnswerDescription).ToList()

我在做什么错？您是否可以（如果可能）为我提供一些可用于将数据加载到视图模型中的代码？

，问题来了

谢谢

Answer 1

如果DetailDescription只是视图模型中的一个字符串，而不是IList，那么我想它是一个ProjectDetailViewModel，因此您的linq应该是：

        var result = _dbContext.ProjectDetails //<==search from details
            .Select(x => new ProjectDetailViewModel
            {
                projectTypeId = x.Project.ProjectTypeId,
                projectType = x.Project.projectType,
                DetailDescription = x.DetailDescription,
                AnswerDescription = x.ProjectDetailsAnswers.Select(a => a.AnswerDescription)
            }).ToList();

但是如果您坚持要从项目中查询：

        var result = _dbContext.Projects.SelectMany(x=>x.ProjectDetails) //<==use SelectMany
            .Select(x => new ProjectDetailViewModel
            {
                projectTypeId = x.Project.ProjectTypeId,
                projectType = x.Project.projectType,
                DetailDescription = x.DetailDescription,
                AnswerDescription = x.ProjectDetailsAnswers.Select(a => a.AnswerDescription)
            }).ToList();

实体框架代码首先将多个级别选择到一个视图模型中

1 个答案: