Configure Many-to-Many Relationship in Code First
The way I understand it, you want to configure one-to-many relationship between EntityGroup and Entity without navigation property in Entity class and using. Docs · Entity Framework · Entity Framework 6 · Fundamentals This topic gives an overview of how Entity Framework manages relationships between entities. In a one-to-many relationship, the foreign key is defined on the table that . Code First maps this property to a non-nullable field in the database. Here, we will learn how to configure One-to-Many relationships between two entities (domain classes) in Entity Framework 6.x using the code-first approach.
In this class, we override the OnModelCreating method. This method is called when the model for a context class EFDbContext has been initialized, but before the model has been locked down and used to initialize the context such that the model can be further configured before it is locked down.
The following is the code snippet for the context class. CreateInstance type ; modelBuilder.
Config file and it connects to that server. In the OnModelCreating method, we used a reflection to map an entity to its configuration class in this specific project.
UnitTest to test the code above. This method creates a database and populates User and UserProfile tables as per their relationship. The following is the code snippet for the UserTest class.C# Entity Framework 6 - Database First - Part 2 - Foreign Keys & Relationships
Run a select query in the database and get results like: Result of User and UserProfile. One-to-Many Relationship The primary key table contains only one record that relates to none, one, or many records in the related table. This is the most commonly used type of relationship.
To understand this relationship, consider an e-commerce system where a single user can make many orders so we define two entities, one for the customer and another for the order. The Customer entity has a collection of Order entity types and the Order entity has a Customer entity type property, that means a customer can make many orders. Now create a class, the CustomerMap class in the EF.
Configure One-to-One relationship in Code First Entity Framework
Here, we use four methods to define the relationship between both entities. The WithMany method allows us to indicate which property in Customer contains the Many relationship.
We add to that the HasForeignKey method to indicate which property of Order is the foreign key pointing back to customer. The WillCascadeOnDelete method configures whether or not cascade delete is on for the relationship. Now, we create another unit test class in the EF. UnitTest Project to test the code above. Many-to-Many Relationship Each record in both tables can relate to any number of records or no records in the other table.
Many-to-many relationships require a third table, known as an associate or linking table, because relational systems can't directly accommodate the relationship.
To understand this relationship, consider an online course system where a single student can join many courses and a course can have many students so we define two entities, one for the student and another for the course.
The Student entity is as in the following code snippet that is defined under EF. Now creates a class StudentMap class in the EF. As you know, to implement Many-to-Many relationships, we need a third table named StudentCourse. The Left key or first key will be that in which we are defining the relationship.
Relationships, navigation properties and foreign keys
Now create a class, the CourseMap class, in the EF. Run the select query in the database and get results like: However, when both ends of the relationship are required or both sides are optional Entity Framework cannot identify the dependent and principal. Instructor ; Configuring a Many-to-Many Relationship The following code configures a many-to-many relationship between the Course and Instructor types.
In the following example, the default Code First conventions are used to create a join table. Courses If you want to specify the join table name and the names of the columns in the table you need to do additional configuration by using the Map method.
ToTable "CourseInstructor" ; m. By convention, Code First always interprets a unidirectional relationship as one-to-many.
Entity Framework Code First: Relationship mapping
For example, if you want a one-to-one relationship between Instructor and OfficeAssignment, where you have a navigation property on only the Instructor type, you need to use the fluent API to configure this relationship. If a foreign key on the dependent entity is not nullable, then Code First sets cascade delete on the relationship. 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.
You can remove these cascade delete conventions by using: