Convert lambda expression to Json in MVC

问题

I get an error ("Cannot convert lambda expression to type 'string' because it is not a delegate type") during converting the lambda expression in controller. I have 3 entities in as below:

Entities:

public class Student
{
    public int ID { get; set; }

    public string Course { get; set; }  

    public int CityID { get; set; }

    public virtual City City { get; set; }
}


public class City
{
    public int ID { get; set; }        

    public string Name { get; set; }

    public int RegionID { get; set; }

    public virtual Region Region { get; set; }

    public virtual ICollection<Student> Students { get; set; }    
}


public class Region
{
    public int ID { get; set; }

    public string Name { get; set; }

    public virtual ICollection<City> Cities { get; set; } 
}

Controller:

public ActionResult Index_Read([DataSourceRequest] DataSourceRequest request)
    {
        var dataContext = repository.Students;
        var students = dataContext.ToDataSourceResult(request, m => new 
        {
            ID = m.ID,
            Course = m.Course,

            City = m.City.Name, //I can get City name and show it in View.
            MyRegionName = m.City.Region.Name //I can get region name and assign it to 
//"MyRegionName" parameter in JSON. However in View I cannot get it using "MyRegionName" paremeter  
        });           

        return Json(students, JsonRequestBehavior.AllowGet);
    }

View:

@model IEnumerable<Student>


@(Html.Kendo().Grid<Student>()
    .Name("Grid")
    .Columns(columns =>
    {
        columns.Bound(m => m.ID);
        columns.Bound(m => m.Course);
        columns.Bound(m => m.City);
        columns.Bound(m => m.MyRegionName);
    })
    .Pageable()
    .Sortable()
    .Filterable()
    .Scrollable()
    .Groupable()    
    .DataSource(dataSource => dataSource
        .Ajax()
        .Read(read => read.Action("Index_Read", "Student"))
    )        
)

Here is the point that may cause the problem in the Controller and View:

City = m.City.Name, //I can get City name and show it in View.
MyRegionName = m.City.Region.Name //I can get region name and assign it to the  "MyRegionName" parameter in JSON. However in View I cannot get it using "MyRegionName" paremeter.

May it be related to that there is City parameter in the Student entity. But there is no MyRegionName property in the City entity.

回答1:

I assume this happens because there is no property called MyRegionName for the Student class.

You have two options

1) Create a ViewModel that looks like your Student model but make it has such property. Also make sure inside the projection function of the ToDataSourceResult you create those new ViewModel types instead of anonymous object.

2) Just use a Template column. e.g.

columns.Template(@<text></text>).Title("MyRegionName").ClientTemplate("#=MyRegionName#");

来源：https://stackoverflow.com/questions/28354301/convert-lambda-expression-to-json-in-mvc