Question

我有以下简单模型，它正在Code First方法中实现。部门和课程有一对多的关系。一个部门可以有很多课程，而一个课程可以只属于一个部门。这是模型。

public class Department
{
    public int DepartmentId { get; set; }
    public string Title { get; set; }
    public string Description { get; set; }
    public virtual ICollection<Course> Courses { get; set; } 
       }

 public class Course
{
    public int CourseId { get; set; }
    public string Title { get; set; }
    public string Description { get; set; }
    public int DepartmentId { get; set; } 
    public virtual Department Department { get; set; }

}

我的问题是我想种下它们。我想在Seed函数中至少有5个值。这是种子功能。

public class DataInitializer : DropCreateDatabaseIfModelChanges<StudentRecordContext>
{
    protected override void Seed(StudentRecordContext context)
{
    var departments = new  List<Department>
     {
        new Department {  DepartmentId = 1, Title = "English", Description ="English     Department",  Courses = new List<Course>() },
        new Department {  DepartmentId= 2,Title = "Chemistry",   Description ="chemistry department", Courses = new List<Course>() },
        new Department {  DepartmentId= 3,Title = "Mahematics", Description ="mathematics department", Courses = new List<Course>() },
        new Department {  DepartmentId= 4,Title = "Philosophy",  Description ="philosophy department", Courses = new List<Course>() },
        new Department {  DepartmentId= 5,Title = "Biology",     Description ="biology department", Courses = new List<Course>() }
    };                                                           
    departments.ForEach( t => context.Departments.Add(t));
    context.SaveChanges();


    var courses = new List<Course>
    {
        new Course { CourseId = 1055, Title = "Classic English",  Description = "Some        Description", DepartmentId = 1 },
        new Course { CourseId = 2055, Title = "Applied Chemistry",  Description = "Some Description", DepartmentId = 2 },
        new Course { CourseId = 2056, Title = "Applied Mathematics", Description = "Some Description", DepartmentId = 3 },
        new Course { CourseId = 3041, Title = "MetaPhysics",  Description = "Some Description", DepartmentId = 4 },
        new Course { CourseId = 3024, Title = "Molecular Biology", Description = "Some Description", DepartmentId = 5 },
    };
    courses.ForEach(t => context.Courses.Add(t));
    context.SaveChanges();

但这不起作用。我是EF和Code First的新手......还有未来的截止日期......任何人都可以帮助我，因为我们正确的方法是播种数据库。

Answer 1

不要在Seed()方法中设置主键。实体框架将知道名称中包含Id的属性将是主键。

在Seed()方法中尝试以下操作：

protected override void Seed(StudentRecordContext context)
{
    var departments = new  List<Department>
    {
        // this will have DepartmentId = 1
        new Department { Title = "English", Description ="English Department",  Courses = new List<Course>() },
        // more departments
    };
    departments.ForEach(d => context.Departments.Add(d));
    context.SaveChanges();

    var courses = new List<Course>
    {
        // this will have CourseId = 1
        new Course { Title = "Classic English",  Description = "Some Description", Department = departments.FirstOrDefault(d => d.DepartmentId == 1) },
        // this will have CourseId = 2
        new Course { Title = "Drama",  Description = "Some Description", Department = departments.FirstOrDefault(d => d.DepartmentId == 1) },
        // both of the above courses will be added to Department with DepartmentId = 1
        // more courses
    };
    courses.ForEach(c => context.Courses.Add(c));
    context.SaveChanges();

    // now add the two courses to the department
    departments[0].Courses.Add(courses[0]); // in list departments at index 0 add course from list courses at index 0
    departments[0].Courses.Add(courses[1]); // in list departments at index 0 add course from list courses at index 1
    context.SaveChanges();
}

Answer 2

由于您自己生成主键，你需要放 [DatabaseGenerated(DatabaseGenerationOption.None)] CourseId和DepartmentId的属性，以便Entity框架知道您正在生成密钥。

更好的选择是继续依赖主键的EntityFramework，但稍微改变一下你的方法

   var courses = new List<Course>
        {
            new Course {Title = "Classic English",  Description = "Some        Description", Department=
     new Department {   Title = "English", Description ="English    
Department",  Courses = new List<Course>() }},
           .....
        };
        courses.ForEach(t => context.Courses.Add(t));

因此，您需要保存课程，并且由于您正在关联该部门，因此将隐式保存。

祝你的截止日期好运！

Answer 3

我是这样做的，你只需要在'parent'之前初始化'children'，不需要SaveChanges（）：

var choices = new List<Choices>
{
    new Choices { Description = "Choice1" },
    new Choices { Description = "Choice2" },
    new Choices { Description = "Choice3" },
    new Choices { Description = "Choice4" }
};

choices.ForEach(c => context.Choices.AddOrUpdate(c));

context.Questions.AddOrUpdate(
    p => p.ID,
    new Question { QuestionText = "Question ?", Choices = choices }
    );

Code First中的一对多关系播种

3 个答案: