实体框架中没有自动生成代码的数据库优先方法 [英] Database-first approach in Entity Framework without auto generated code
问题描述
我想知道，如果有任何方式，
提前使用数据库优先方法与手动生成的类（模型）（就像代码优先方法）一样，
但不使用自动生成实体框架使用数据库优先方法创建的代码？
我有3个类（前两个学生和课程有很多关系），代表模型：
第一个是学生：
public class Student
{
public int StudentID {get; set;}
public string Name {get; set;}
public DateTime BirthDate {get; set;}
public ICollection< StudentToCourse> StudentToCourses {get;组; }
public Student（）
{
StudentToCourses = new List< StudentToCourse>（）;
}
}
然后课程：
public class Course
{
public int CourseID {get;组; }
public string CourseName {get;组; }
public ICollection< StudentToCourse> StudentToCourses {get;组; }
public Course（）
{
StudentToCourses = new List< StudentToCourse>（）;
}
}
和关系/中级课程附加属性StudentToCourse：
public class StudentToCourse
{
[Key，Column（Order = 0）]
public int StudentID {get;组; }
[Key，Column（Order = 1）]
public int CourseID {get;组; }
[Key，Column（Order = 2）]
public DateTime Date {get;组; }
public virtual Student Student {get;组; }
public virtual Course Course {get;组; }
// public ICollection< Student>学生{get;组; }
// public ICollection< Course>课程{get;组; }
public int Grade {get;组; }
}
另外，我创建了数据库，在VS中使用LocalDb功能2013年
我有3个表：
课程：
CREATE TABLE [dbo]。[课程]
（
[CourseID] INT NOT NULL主键标识，
[CourseName] NVARCHAR（100）NOT NULL，
）
学生：
CREATE TABLE [dbo]。[学生]
（
[StudentID] INT NOT NULL主键标识，
[名称] NVARCHAR（50）NOT NULL，
[出生日期] DATETIME NOT NULL，
）
关系表StudentsToCourses：
CREATE TABLE [dbo]。[StudentsToCourses]
（
[StudentID] INT参考学生（StudentID）NOT NULL，
[CourseID] INT参考课程（CourseID）NOT NULL，
[日期] DATETIME NOT NULL，
[成绩] INT NOT NULL，
PRIMARY KEY（StudentID，CourseID，Date）
）
不幸的是，我没有运气这个方法，我确实得到学生的数据，但是我没有从关系表中收到数据，我不能收到每个学生的所有相关成绩。
我搜索了相关的主题在谷歌和stackoverflow，但所有这些主题对我来说没有帮助，虽然上面的例子我发现在这个话题。
As我怀疑，问题不在于您是否可以独立拥有数据库和类模型。当然可以！所有这些生成工具和迁移的东西只能达到一个目标：使生活更轻松，帮助您保持两个模型的同步。但是你也可以自己做这个工作。最终的结果总是：两个模型 - 在运行时 - 不要互相交互。 （不要互动？不，不是这样，必须有一个中间人，一个ORM，连接两个世界。）
你没有得到的原因数据是因为不会发生延迟加载。您的陈述是
var listOfGrades = _context.Students.Where（s => s.Name.StartsWith（J） ）
.FirstOrDefault（）。StudentToCourses;
这需要懒惰加载，因为 FirstOrDefault（）语句执行查询的第一部分。它呈现一个学生，随后 StudentToCourses 被访问。但是这些不加载，因为集合不是 virtual 。应该是
public virtual ICollection< StudentToCourse> StudentToCourses {get;组; }
这将启用EF来覆盖能够延迟加载的动态代理对象中的集合。 / p>
但是，当然，在一个语句中获取集合效率更高，例如：
.Where（s => s.Name.StartsWith（J））
。 FirstOrDefault（）StudentToCourses。
I wonder, if there is any way , to use Database-first approach with manually generated classes (models) in advance(just like Code-first approach), but without using auto-generated code which Entity Framework creates using Database-first approach? I have 3 Classes(first two of them Student and Courses have many to many relationship), which represents models: First one is Student:
public class Student
{
public int StudentID { get; set;}
public string Name { get; set;}
public DateTime BirthDate { get; set;}
public ICollection<StudentToCourse> StudentToCourses { get; set; }
public Student()
{
StudentToCourses = new List<StudentToCourse>();
}
}
Then Course:
public class Course
{
public int CourseID { get; set; }
public string CourseName { get; set; }
public ICollection<StudentToCourse> StudentToCourses { get; set; }
public Course()
{
StudentToCourses = new List<StudentToCourse>();
}
}
And Relation/Intermediate Class with additional properties StudentToCourse:
public class StudentToCourse
{
[Key, Column(Order = 0)]
public int StudentID { get; set; }
[Key, Column(Order = 1)]
public int CourseID { get; set; }
[Key, Column(Order = 2)]
public DateTime Date { get; set; }
public virtual Student Student { get; set; }
public virtual Course Course { get; set; }
//public ICollection<Student> Students { get; set; }
//public ICollection<Course> Courses { get; set; }
public int Grade { get; set; }
}
Also, i created Database, using LocalDb feature in VS 2013
I have 3 Tables: Courses:
CREATE TABLE [dbo].[Courses]
(
[CourseID] INT NOT NULL PRIMARY KEY IDENTITY,
[CourseName] NVARCHAR(100) NOT NULL,
)
Students:
CREATE TABLE [dbo].[Students]
(
[StudentID] INT NOT NULL PRIMARY KEY IDENTITY,
[Name] NVARCHAR(50) NOT NULL,
[BirthDate] DATETIME NOT NULL,
)
Relation Table StudentsToCourses:
CREATE TABLE [dbo].[StudentsToCourses]
(
[StudentID] INT REFERENCES Students(StudentID) NOT NULL,
[CourseID] INT REFERENCES Courses(CourseID) NOT NULL,
[Date] DATETIME NOT NULL,
[Grade] INT NOT NULL,
PRIMARY KEY (StudentID, CourseID, Date)
)
Unfortunately, i have no luck with this approach, i do get students' data but i don't receive data from relational table and i can't receive all related grades per student.
I searched for related topics in google and in stackoverflow , but all those topics weren't helpful for me, although the example above i found in this topic.
As I suspected, the problem is not whether or not you can have a database and a class model independently. Of course you can! All these generation tools and migration stuff only serve one goal: making life easier, help you keeping both models in sync. But you can do that job yourself just as well. The end result is always: two models that – at runtime – don't interact with each other whatsoever. (Don't interact? No, not as such. There must be a middleman, an ORM, to connect both worlds.)
The reason why you don't get data is because lazy loading does not occur. Your statement is
var listOfGrades = _context.Students.Where(s => s.Name.StartsWith("J"))
.FirstOrDefault().StudentToCourses;
This requires lazy loading, because the FirstOrDefault() statement executes the first part of the query. It renders a Student of which subsequently the StudentToCourses are accessed. But these don't load because the collection is not virtual. It should be
public virtual ICollection<StudentToCourse> StudentToCourses { get; set; }
This enables EF to override the collection in a dynamic proxy object that is capable of lazy loading.
But of course is is more efficient to get the collection in one statement, for example:
var listOfGrades = _context.Students.Include(s => s.StudentToCourses)
.Where(s => s.Name.StartsWith("J"))
.FirstOrDefault().StudentToCourses;
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