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实体框架代码首先在视图模型中选择多个级别

entity-framework-6 asp.net-mvc c#

-1

ev vk · 技术社区 · 6 年前

很好的一天,

我正在使用ASPNET MVC,带C#和实体框架我的codefirst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; }
}

正如你所看到的,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; }
}

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viewmodel

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
}

到目前为止我得到的是这个代码:

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:>无法将此代码中的字符串转换为列表。 n.AnswerDescription.Select(b =>b.AnswerDescription).ToList()

我做错什么了?如果可能的话,你能提供一些代码来加载我的viewmodel和数据吗?

,问题来了

谢谢

1 回复 | 直到 6 年前

Dongdong 6 年前

如果DetailDescription只是viewmodel中的一个字符串,而不是IList,那么我猜它是一个ProjectDetailViewModel,所以您的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();

但如果你坚持从项目中查询:

        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();