Configuring One To Many Relationships in Entity Framework Core | Learn Entity Framework Core
Jul 11, EntityTYpeConfiguration is an important class that allows configuration to In the code snippet above we defined a one-to-one relationship. Feb 27, The following model represents companies and employees with an inverse navigation property defined in the dependent entity (Employee). Sep 23, In previous versions of Entity Framework, this model definition was sufficient for EF to imply the correct type of relationship and to generate the.
By default, Entity Framework uses the Code First conventions to map your classes to the database schema.
Configure One-to-Zero-or-One Relationship in Entity Framework 6
If you use the Code First naming conventions, in most cases you can rely on Code First to set up relationships between your tables based on the foreign keys and navigation properties that you define on the classes. If you do not follow the conventions when defining your classes, or if you want to change the way the conventions work, you can use the fluent API or data annotations to configure your classes so Code First can map the relationships between your tables.
Introduction When configuring a relationship with the fluent API, you start with the EntityTypeConfiguration instance and then use the HasRequired, HasOptional, or HasMany method to specify the type of relationship this entity participates in.Access 2016 - Relationships - How To Create One To Many Relationship in Database Between Two Tables
The HasRequired and HasOptional methods take a lambda expression that represents a reference navigation property. The HasMany method takes a lambda expression that represents a collection navigation property.
Programming Entity Framework: Code First by Rowan Miller, Julia Lerman
These methods have overloads that do not take arguments and can be used to specify cardinality with unidirectional navigations. You can then configure foreign key properties by using the HasForeignKey method.
This method takes a lambda expression that represents the property to be used as the foreign key. The OfficeAssignment has the InstructorID property that is a primary key and a foreign key, because the name of the property does not follow the convention the HasKey method is used to configure the primary key.
The one-to-many relationship can be configured in the following ways. By using Fluent API Configurations Conventions for One-to-Many Relationships There are certain conventions in Entity Framework which if followed in entity classes domain classes will automatically result in a one-to-many relationship between two tables in the database.
- One to Many Relationship in Entity Framework
- Configuring One To Many Relationships in Entity Framework Core
- Fluent API - Relationships
You don't need to configure anything else. Let's look at an example of all the conventions which create a one-to-many relationship. Convention 1 We want to establish a one-to-many relationship between the Student and Grade entities where many students are associated with one Grade.
Fluent API - Relationships - EF6 | Microsoft Docs
It means that each Student entity points to a Grade. This can be achieved by including a reference navigation property of type Grade in the Student entity class, as shown below. So, there can be many students in a single grade. Convention 2 Another convention is to include a collection navigation property in the principal entity as shown below.
This also results in a one-to-many relationship between the Student and Grade entities. This example produces the same result in the database as convention 1. Convention 3 Including navigation properties at both ends will also result in a one-to-many relationship, as shown below.
Configure One-to-One relationship in Code First Entity Framework
Convention 4 A fully defined relationship at both ends will create a one-to-many relationship, as shown below. This will create a one-to-many relationship with the NotNull foreign key column in the Students table, as shown below. If the data type of GradeId is nullable integer, then it will create a null foreign key. However, you may configure relationships using Fluent API at one place to make it more maintainable.