没有流利的API的C＃多对多关系代码

Question

I'm trying to understand Entity Framework Code First.

Is it possible to configure a many-to-many relationship without using fluent API but just DataAnnotation? For example in this tutorial I don't understand if the two examples are the same thing but done in different ways or if they have to exist together.

• If they are different ways for the same thing, what is actually the difference?

• And if they have to coexist, what is the API "part" doing?

Answer 1

Indeed you are right.

This paragraph:

Configure Many-to-Many relationship using DataAnnotation:

Student class should have a collection navigation property for Course, and Course should have a collection navigation property for student,

is wrong. Because the many-to-many relationship in the sample code in created automatically by convention when you add a collection in each class. The only data annotation that is used is Required attribute which is not implied in the many-to-many relationship.

BTW the section about "Configure Many-to-Many relationship using Fluent API" is correct but in their sample code they use it only put a custom name to the foreign key in the join table instead of letting Code First generating it. Foreing key renaming can be done too with Data Annotation by using ForeignKey attribute.

Answer 2

They're two different ways of configuring the database. They can coexist, but they don't have to; you can use just one or the other. If you do use both, the Fluent API takes precedence over the data annotations, but the data annotations still take precedence over the default conventions.

The difference is that API allows a more exacting degree of control, in exchange for being (arguably) more complicated. The example you linked does show two different ways of accomplishing effectively the same thing, and you could use one or the other if you wanted to create that specific many-to-many relationship. But the API method would be more configurable if you wanted to do something odd with that CourseStudents (or StudentCourse) table, while the annotation method would be more limited but is easier to read at a glance if you don't need the extra functionality.