[翻译]ADO.NET Entity Framework Beta2(九)/快速入门（实体框架）（4）/查询实体及关系

Imports SchoolModel

Imports System.Data.Objects

using System.Data.Objects;

using SchoolModel;

' Create an ObjectContext instance based on SchoolEntity.

' 基于学校实体创建一个实体关联对象

Private schoolContext As SchoolEntities

// Create an ObjectContext instance based on SchoolEntity.

// 基于学校实体创建一个实体关联对象

private SchoolEntities schoolContext;

' Initialize the ObjectContext.

' 初始化实体关联对象

schoolContext = New SchoolEntities()

' Define the DataGridView.

' 定义DataGridView

studentClasses.Columns.Add("courseName", "Course Name")

studentClasses.Columns.Add("courseDate", "Date Completed")

studentClasses.Columns.Add("courseGrade", "Grade")

studentClasses.Columns.Add("courseCredits", "Credits")

' Get students as all people who have enrollment dates.

' 获得所有拥有入学日期的学生作为全体集合

Dim students As ObjectQuery(Of Person) = _

schoolContext.Person.Where( _

"it.EnrollmentDate IS NOT NULL").OrderBy("it.LastName")

' Define the query path for queries that return a Person object

'and bind the ComboBox to the collection returned by the query.

' 为查询定义查询路径以返回一个Person对象

'然后将ComboBox控件绑定到查询所返回的集合上

Me.studentsList.DataSource = students.Include("Enrollment.Course")

Me.studentsList.DisplayMember = "LastName"

// Initialize the ObjectContext.

//初始化实体关联对象

schoolContext = new SchoolEntities();

// Define the DataGridView.

//  定义DataGridView

studentClasses.Columns.Add("courseName", "Course Name");

studentClasses.Columns.Add("courseDate", "Date Completed");

studentClasses.Columns.Add("courseGrade", "Grade");

studentClasses.Columns.Add("courseCredits", "Credits");

// Get students as all people who have enrollment dates.

// 获得所有拥有入学日期的学生作为全体集合

ObjectQuery<Person> students = schoolContext.Person.Where(

"it.EnrollmentDate IS NOT NULL").OrderBy("it.LastName");

// Define the query path for queries that return a Person object

// and bind the ComboBox to the collection returned by the query.

// 为查询定义查询路径以返回一个Person对象

// 然后将ComboBox控件绑定到查询所返回的集合上

this.studentsList.DataSource = students.Include("Enrollment.Course");

this.studentsList.DisplayMember = "LastName";

Try

' clear existing rows from the DataGridView.

' 将DataGridView内的现有行清空

studentClasses.Rows.Clear()

' Get the Person object for the selected student.

' 获取被选中的学生对象

Dim student As Person = CType(studentsList.SelectedItem, Person)

Dim enrollment As Enrollment

For Each enrollment In student.Enrollment

' Create an array of row cells.

' 创建一个单元格数组作为行

Dim row() As Object = New Object(4) {}

' Load object values from entities.

' 获取实体的各种值

row(0) = enrollment.Course.Title

row(1) = enrollment.Course.EndDate

row(2) = enrollment.Grade

row(3) = enrollment.Course.Credits

' Add the new row to the DataGridView.

' 将新行添加到DataGridView

studentClasses.Rows.Add(row)

studentClasses.AutoResizeColumns(DataGridViewAutoSizeColumnsMode.AllCells)

Next

Catch ex As Exception

MessageBox.Show(ex.Message)

End Try

try

{

// clear existing rows from the DataGridView.

// 将DataGridView内的现有行清空

studentClasses.Rows.Clear();

// Get the Person object for the selected student.

// 获取被选中的学生对象

Person student = (Person)studentsList.SelectedItem;

foreach (Enrollment enrollment in student.Enrollment)

{

// Create an array of row cells.

// 创建一个单元格数组作为行

object[] row = new object[4];

// Load object values from entities.

// 获取实体的各种值

row[0] = enrollment.Course.Title;

row[1] = enrollment.Course.EndDate;

row[2] = enrollment.Grade;

row[3] = enrollment.Course.Credits;

// Add the new row to the DataGridView.

// 将新行添加到DataGridView

studentClasses.Rows.Add(row);

studentClasses.AutoResizeColumns(DataGridViewAutoSizeColumnsMode.AllCells);

}

}

catch (Exception ex)

{

MessageBox.Show(ex.Message);

}

' Dispose the object context.

' 释放实体关联对象

schoolContext.Dispose()

// Dispose the object context.

// 释放实体关联对象

schoolContext.Dispose();