通过 LINQ 加入列表

Question

我有两个对象列表

任务

    public string ProjectNumber { get; set; }
    public string Name { get; set; }
    public string ProjectManager { get; set; }
    public string Customer { get; set; }

项目

    public string Number { get; set; }
    public string Title { get; set; }
    public string Manager { get; set; }
    public string Customer { get; set; }

示例数据

任务

Projectnumber | Name          | ProjectManager | Customer 
    7780      | Buy container | NULL           | NULL
    7781      | Block budget  | NULL           | NULL

项目

Nubmer        | Title         | Manager        | Customer 
    7780      | Surface       | Bill Gates     | Microsoft 
    7781      | iWatch        | Tim Cook       | Apple

我想得到一个List<Task> 作为结果：

Projectnumber | Name          | ProjectManager | Customer 
    7780      | Buy container | Bill Gates     | Microsoft 
    7781      | Block budget  | Tim Cook       | Apple

到目前为止我尝试了什么：

List<Task> spTasks = SPRepo.GetAllTasksByResourceTeam();
List<Project> projects = PWARepo.GetAllProjects();

    List<Task> joinedSPTasks = from a in spTasks
                        join b in projects on a.ProjectNumber equals b.Number
                        select new Task() {
                        a.Projectnumber = a.Projectnumber,
                        a.Name = a.Name,
                        a.ProjectManager = b.ProjectManager,
                        a.Customer = b.Manager
                        };

为什么我不能为属性赋值？我在 Visual Studio 中收到以下错误：

Error: Invalid anonymous type member decorator. Anonymous type members must be declared with a member assignment simple name or member access.

注意：这些对象列表来自不同的来源。无法将它们加入源系统（例如通过表连接的数据库）！

Answer 1

目前尚不清楚您是要更新当前任务还是创建新任务。

新建一个会是这样的

var joinedSPTasks = from a in spTasks
                    join b in projects on a.ProjectNumber equals b.Number
                    select new Task(){
                        Projectnumber = a.Projectnumber,
                        Name = a.Name,
                        ProjectManager = b.ProjectManager,
                        Customer = b.Manager
                        };

Answer 2

List<Task> joinedSPTasks = from a in spTasks
                    join b in projects on a.ProjectNumber equals b.Number
                    select new Task(){
                        ProjectNumber = a.Projectnumber,
                        Name = a.Name,
                        ProjectManager = b.ProjectManager,
                        Customer = b.Manager
                        };

或

var joinedSPTasks = from a in spTasks
                    join b in projects on a.ProjectNumber equals b.Number
                    select new {
                        ProjectNumber = a.Projectnumber,
                        Name = a.Name,
                        ProjectManager = b.ProjectManager,
                        Customer = b.Manager
                        };

删除“a”。从匿名成员名称开始。第二种选择是使用匿名类型。你需要使用var关键字来声明匿名类型

Answer 3

您正在选择动态对象中的值。而不是使用 select new{，而是使用 select new Task{

        List<Task> joinedSPTasks = (from a in spTasks
                join b in projects on a.ProjectNumber equals b.Number
                select new Task{
                    Projectnumber = a.Projectnumber,
                    Name = a.Name,
                    ProjectManager = b.ProjectManager,
                    Customer = b.Manager
                    }).ToList();

Answer 4

你创建的匿名类型是错误的——应该是这样的：

                joinedSPTasks = from a in spTasks
                join b in projects on a.ProjectNumber equals b.Number
                select new {
                    Projectnumber = a.Projectnumber,
                    Name = a.Name,
                    ProjectManager = b.ProjectManager,
                    Customer = b.Manager
                    };

您实际上可以删除参数命名并像这样编写它：

select new { a.Projectnumber, a.Name, b.ProjectManager, b.Manager };