Code first entity framework one to many relationship definition

Configure One-to-One relationship in Code First Entity Framework

code first entity framework one to many relationship definition

In a one-to-many relationship, the foreign key is defined on the table that In Entity Framework, an entity can be related to other entities through an To configure relationships in Code First, see Data Annotations and Fluent. How to use the Fluent API to configure one to many relationships in Entity with an inverse navigation property defined in the dependent entity. Configure Many-to-Many Relationships in Code-First. Here, we The following is the context class that includes the Student and Course entities. public class.

The following code snippet shows the same model that was created with Code First. For information on setting up relationships in your model, see the following pages.

Creating and modifying relationships In a foreign key association, when you change the relationship, the state of a dependent object with an EntityState. Unchanged state changes to EntityState. In an independent relationship, changing the relationship does not update the state of the dependent object. The following examples show how to use the foreign key properties and navigation properties to associate the related objects.

With foreign key associations, you can use either method to change, create, or modify relationships. With independent associations, you cannot use the foreign key property. By assigning a new value to a foreign key property, as in the following example.

Configure One-To-Many Relationships In Entity Framework Using Code First Approach

DepartmentID; The following code removes a relationship by setting the foreign key to null. Note, that the foreign key property must be nullable. Synchronization does not occur because the object context does not contain permanent keys for added objects until they are saved.

If you must have new objects fully synchronized as soon as you set the relationship, use one of the following methods. The following code creates a relationship between a course and a department. If the objects are attached to the context, the course is also added to the department. Courses collection, and the corresponding foreign key property on the course object is set to the key property value of the department.

Relationships

If you are working with Entity Framework that is based on. You can also set the current value to null using the following method.

code first entity framework one to many relationship definition

For example, you can add an object of type Course to the department. This operation creates a relationship between a particular course and a particular department.

code first entity framework one to many relationship definition

If the objects are attached to the context, the department reference and the foreign key property on the course object will be set to the appropriate department. Add newCourse ; By using the ChangeRelationshipState method to change the state of the specified relationship between two entity objects.

This method is most commonly used when working with N-Tier applications and an independent association it cannot be used with a foreign key association.

code first entity framework one to many relationship definition

Also, to use this method you must drop down to ObjectContext, as shown in the example below. In the following example, there is a many-to-many relationship between Instructors and Courses.

Added parameter, lets the SchoolContext know that a relationship has been added between the two objects: Added ; Note that if you are updating not just adding a relationship, you must delete the old relationship after adding the new one: Deleted ; Synchronizing the changes between the foreign keys and navigation properties When you change the relationship of the objects attached to the context by using one of the methods described above, Entity Framework needs to keep foreign keys, references, and collections in sync.

Entity Framework automatically manages this synchronization also known as relationship fix-up for the POCO entities with proxies. For more information, see Working with Proxies. If you are using POCO entities without proxies, you must make sure that the DetectChanges method is called to synchronize the related objects in the context.

The HasOptional method configures the Address navigation property in Student entity as optional not required when saving the Student entity. Then, the WithRequired method makes the Student navigation property of StudentAddress as required required when saving the StudentAddress entity; it will throw an exception when the StudentAddress entity is saved without the Student navigation property. Thus, you can configure a one-to-Zero-or-one relationship between two entities where the Student entity can be saved without attaching the StudentAddress object to it but the StudentAddress entity cannot be saved without attaching an object of the Student entity.

This makes one end required. EF API will create the following tables in the database. Configure a One-to-One relationship using Fluent API We can configure a one-to-One relationship between entities using Fluent API where both ends are required, meaning that the Student entity object must include the StudentAddress entity object and the StudentAddress entity must include the Student entity object in order to save it.

These will always be one-to-zero-or-one relationships. Address makes the Address property of StudentAddress as required and. Student makes the Student property of the StudentAddress entity as required.

One to Many Relationship in Entity Framework - tekTutorialsHub

Thus it configures both ends as required. So now, when you try to save the Student entity without the StudentAddress entity without the Student, it will throw an exception. The entities will appear like the diagram shown below: