Managing One To Many Relationships With Entity Framework Core | Learn Entity Framework Core
For many-to-many relationships, the Entity Framework doesn't expose the join table directly, so you add and remove entities to and from the. The problem with detached entities is that the data context has no way of knowing what schema allocated PK ID values) whereas the other two tables the ID must be specified. Updating a Many-to-Many Relationship. Entity Framework Relationships - Learn Entity Framework starting from Overview, There are three types of relationships between tables and the relationship.
You can use data annotations.
Relationships, navigation properties and foreign keys - EF6 | Microsoft Docs
And finally, you can configure relationships by convention. Data Annotations I can also set a property to be required with data annotations.
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- Managing One To Many Relationships With Entity Framework Core
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Using the same example, I can set EquipmentType to be required by including an annotation when declaring it in the model class: By Convention So what is configuration by convention?
When you follow some simple rules on property types and names, Entity Framework will auto-configure many of the software and database features. Configuring Relationships in Entity Framework Configuring scalar non-relational properties is quite straightforward, but when it comes to entity relationships, it can be more tricky to decide which approach is best for configuring them. By default, when I delete a Student, I will get a referential integrity error: So how do I fix this?
The official Microsoft documentation recommends manually deleting each foreign key for dependent entities: If we look at the documentation for Entity Framework 6 it says that: If a foreign key on the dependent entity is nullable, Code First does not set cascade delete on the relationship, and when the principal is deleted the foreign key will be set to null. Entity Framework should now set the foreign keys to null for these entities when I delete a student.
The foreign key is defined in the table that represents the many end of the relationship.
c# - Insert/Update Many to Many Entity Framework . How do I do it? - Stack Overflow
For example, in the above diagram Student and Enrollment tables have one-tomany relationship, each student may have many enrollments, but each enrollment belongs to only one student. In entity framework, these relationship can be created with code as well.
Following is an example of Student and Enrollment classes which are associated with one to many relationship. Many-to-Many Relationship In many-to-many relationship, a row in table A can have many matching rows in table B, and vice versa.
You can create such a relationship by defining a third table, called a junction table, whose primary key consists of the foreign keys from both table A and table B.
For example, the Student and Course tables have many-to-many relationship that is defined by one-to-many relationship from each of these tables to the Enrollment table.
Configuring Entity Relationships with Entity Framework
The following code contains the Course class and the above two classes, i. One-to-One Relationship In a one-to-one relationship, a row in table A can have no more than one matching row in table B, and vice versa. A one-to-one relationship is created if both of the related columns are primary keys or have unique constraints.