Question

我正在使用Entity Framework创建App。我从Database.here加载了数据库模型在Course表Department中是Navigation Property，DepartmentID是外来的key.I创建了一个gridview并将其Datasource设置为Course Table，但是我希望看到Deaptment Name而不是department ID。我可以使用导航属性，如Department.count但是我怎么能使用navigation属性从Department Table获取数据（部门名称）。任何人都可以帮助我这是我的代码

       var result = (from o in ctx.Courses.Include("Department")
                     where o.Title == TextBox2.Text
                      select o
                      ).First();

        //GridView4.DataSourceID="";
        GridView3.DataSource=result;

        GridView3.DataBind();

如果我不使用First Function，那么我无法访问Department Name属性，如果我使用First（）它说

Data source is an invalid type.  It must be either an IListSource, IEnumerable, or IDataSource.

请告诉我如何解决它？

Answer 1

var result = (from c in dbContext.Course
             select c).First();
if(!result.Department.IsLoaded)
   {
      result.Department.Load(); //this will load the course.Department navigation property

   }

//Assuming you have 1 - 1 relationship with course to department
string departmentName = result.Department.Name;

或者如果你与部门有1 - M的关系，那么：

foreach(Department d in result.Department)
{
Console.WriteLine(d.Name);
}

编辑：
而不是尝试加载部门做以下

if(!result.DepartmentReference.IsLoaded)
{
result.DepartmentReference.Load()
}

How to: Explicitly Load Related Objects

Answer 2

我认为Northwind中的产品和类别表与您的需求相似。我会写一个这样的查询：

        var ctx = new NorthwindEntities();
        var query = from prod in ctx.Products
                    where prod.ProductName.StartsWith("C")
                    select new { prod.ProductName, prod.UnitPrice, prod.Category.CategoryName };

使用Navigation属性获取数据

2 个答案: