ADO.NET Entity Framework查询实体和关联（实体框架快速入门）

在本任务中，您将针对在 School 模型中表示实体和关联的 CLR 对象创建强类型查询，并将显示控件绑定到从这些查询中返回的对象集合。

在 School 数据库中查询系

1. Imports (Visual Basic) 语句，以引用从 School 数据库和实体命名空间中创建的模型。

   using System.Data.Objects;
   
                       using System.Data.Objects.DataClasses;
   

    

2. ObjectContext 实例的代码。

   //Create an ObjectContext instance based on SchoolEntityprivate        SchoolEntities schoolContext;
   
3. CourseViewer 窗体。

4. courseViewer _Load 事件处理程序方法。

5. Department 对象的集合绑定到 departmentList 控件。

   //Initialize the ObjectContext
   schoolContext = new SchoolEntities();
   
   
                       // Define a query that returns all Department

    // objects and course objects, ordered by name.var departmentQuery =
                       from d
                       in schoolContext.Departments.Include(
                       "Courses")
                        
                       orderby d.Name
                        
                       select d;
   
                       try
   {
      
                       // Bind the ComboBox control to the query, // which is executed during data binding.this.departmentList.DisplayMember =
                       "Name";
      
                       this.departmentList.DataSource = departmentQuery;
   }
   
                       catch (Exception ex)
   {
       MessageBox.Show(ex.Message);
   }
   
   
                    

显示所选系的课程

1. departmentList 控件。

   departmentList_SelectedIndexChanged 事件处理程序方法。

2. 粘贴以下用于加载与所选系相关的课程的代码。

   try
               {
                  
                       //Get the object for the selected department.
                   Department department = (Department)
                       this.departmentList.SelectedItem;
   
                  
                       //Bind the grid view to the collection of Course objects// that are related to the selected Department object.
                   courseGridView.DataSource = department.Courses;
   
                  
                       // Hide the columns that are bound to the navigation properties on Course.
                   courseGridView.Columns[
                       "Department"].Visible =
                       false;
                   courseGridView.Columns[
                       "StudentGrades"].Visible =
                       false;
                   courseGridView.Columns[
                       "OnlineCourse"].Visible =
                       false;
                   courseGridView.Columns[
                       "OnsiteCourse"].Visible =
                       false;
                   courseGridView.Columns[
                       "People"].Visible =
                       false;
                   courseGridView.Columns[
                       "DepartmentId"].Visible =
                       false;
   
                   courseGridView.AllowUserToDeleteRows =
                       false;
           courseGridView.AutoResizeColumns(DataGridViewAutoSizeColumnsMode.AllCells);
               }
              
                       catch (Exception ex)
               {
                   MessageBox.Show(ex.Message);
               }
   后续步骤

插入和更新数据（实体框架快速入门）。

请参见

概念

查询概念模型（实体框架）

使用实体数据

其他资源

示例（实体框架）