Question

需要一些帮助来破译从位于中间层类的LINQ查询中传回数据的正确方法......

我可以正常使用第一个查询，但我无法从父实体或Project实体中选择任何特定列。

public List<Project> GetProjects()
        {
            try
            {
                using (YeagerTechEntities DbContext = new YeagerTechEntities())
                {
                    DbContext.Configuration.ProxyCreationEnabled = false;
                    DbContext.Database.Connection.Open();

                    IEnumerable<Project> project = DbContext.Projects.Where(p => p.ProjectID > 0);

                    List<Project> myProjects = new List<Project>();

                    myProjects = project.ToList();

                    return myProjects;

                }
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

我无法使用第二个查询，因为我在“DbContext.Projects.Where（p =＆gt; p.ProjectID＆gt; 0）上获得了设计时编译错误”将AnonymousType＃1转换为IEnumerable“。选择“

public List<Project> GetProjects()
        {
            try
            {
                using (YeagerTechEntities DbContext = new YeagerTechEntities())
                {
                    DbContext.Configuration.ProxyCreationEnabled = false;
                    DbContext.Database.Connection.Open();

                    IEnumerable<Project> project = DbContext.Projects.Where(p => p.ProjectID > 0).Select(s => new
                    {
                        s.CategoryID,
                        s.Quote,
                        s.Name,
                        priname = s.Priority.Description,
                        catname = s.Category.Description,
                        statname = s.Status.Description,
                        s.Customer.Email,
                        s.Customer.City
                    });


                    List<Project> myProjects = new List<Project>();

                    myProjects = project.ToList();

                    return myProjects;

                }
            }

我无法使用第三个查询，因为我在“proj.ToList（）”上获得了与上面相同的设计时编译错误。

public List<Project> GetProjects()
        {
            try
            {
                using (YeagerTechEntities DbContext = new YeagerTechEntities())
                {
                    DbContext.Configuration.ProxyCreationEnabled = false;
                    DbContext.Database.Connection.Open();

                    IEnumerable<Project> project = DbContext.Projects.Where(p => p.ProjectID > 0);

                    var proj = project.Select(s => new
                    {
                        s.CategoryID,
                        s.Quote,
                        s.Name,
                        priname = s.Priority.Description,
                        catname = s.Category.Description,
                        statname = s.Status.Description,
                        s.Customer.Email,
                        s.Customer.City
                    }
                );



                    List<Project> myProjects = new List<Project>();

                    myProjects = proj.ToList();

                    return myProjects;

                }
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

有人可以告诉我如何从中间层对象正确传递LINQ查询的内容吗？回到客户端我知道如何使用带有“var”语法的查询从后面的代码或Controller中显然做到这一点。

修订版＃1

基于jalpesh's answer below我添加了一个名为 ProjectFields 的类（在同一个项目中），并将该类合并到LINQ查询中。但是，我得到一个设计时编译错误“无效的匿名类型成员声明。必须使用成员分配，简单名称或成员访问声明匿名类型成员。”

设计时编译错误位于 projflds 属性的每一行。

我知道你们要我做什么。基本上，创建一个新类并在层之间发送该类。 我在这里做错了什么????

以下是我创建的新课程：

public class ProjectFields
{
    public short CategoryID { get; set; }
    public decimal Quote { get; set; }
    public string Name { get; set; }
    public string PriorityName { get; set; }
    public string CategoryName { get; set; }
    public string StatusName { get; set; }
    public string Email { get; set; }
    public string City { get; set; }
}

下面是修改后的LINQ查询，我收到错误：

public List<Project> GetProjects()
{
    try
    {
        using (YeagerTechEntities DbContext = new YeagerTechEntities())
        {
            DbContext.Configuration.ProxyCreationEnabled = false;
            DbContext.Database.Connection.Open();

            IEnumerable<Project> project = DbContext.Projects.Where(p => p.ProjectID > 0);
            ProjectFields projflds = new ProjectFields();

            var proj = project.Select(s => new
            {
                projflds.CategoryID = s.CategoryID,
                projflds.Quote = s.Quote,
                projflds.Name = s.Name,
                projflds.PriorityName = priname = s.Priority.Description,
                projflds.CategoryName = catname = s.Category.Description,
                projflds.StatusName = statname = s.Status.Description,
                projflds.Email = s.Customer.Email,
                projflds.City = s.Customer.City
            });

            List<Project> myProjects = new List<Project>();

            myProjects = project.ToList();

            return myProjects;
        }
    }
    catch (Exception ex)
    {
        throw ex;
    }
}

Answer 1

您正在使用选择新属性创建AnonymousType，这就是该属性与项目类不同的原因。下面将创建一个新类型，所以首先你需要列出到列表，你不能直接投射它。

var proj = project.Select(s => new
                {
                    s.CategoryID,
                    s.Quote,
                    s.Name,
                    priname = s.Priority.Description,
                    catname = s.Category.Description,
                    statname = s.Status.Description,
                    s.Customer.Email,
                    s.Customer.City
                }

做一些像下面的链接。

Convert Anonymous Type to Class

var proj = project.Select(s => new Project
            {
                Name=s.Name
            }

Answer 2

你几乎只有几个最终解决方案：

public List<ProjectFields> GetProjects()
{
    try
    {
        using (YeagerTechEntities DbContext = new YeagerTechEntities())
        {
            DbContext.Configuration.ProxyCreationEnabled = false;
            DbContext.Database.Connection.Open();

            IQueryable<Project> project = DbContext.Projects.Where(p => p.ProjectID > 0);
            var proj = project.Select(s => new ProjectFields
            {
                CategoryID = s.CategoryID,
                Quote = s.Quote,
                Name = s.Name,
                PriorityName = s.Priority.Description,
                CategoryName = s.Category.Description,
                StatusName = s.Status.Description,
                Email = s.Customer.Email,
                City = s.Customer.City
            });

            List<ProjectFields> myProjects = project.ToList();

            return myProjects;
        }
    }
    catch (Exception ex)
    {
        throw ex;
    }
}

尝试从中间层类传回LINQ查询

修订版＃1

2 个答案: