Configuring One To One Relationships In Entity Framework Core | Learn Entity Framework Core
I try to set a 1 to relation in EDMX model. The Model is generate by Database first. Table A: id_a. Table B: id_b. id_a. With Foreign Key. To configure relationships in Code First, see Data Annotations and Fluent . based on the foreign key value that is currently in the database. Configure One-to-Many Relationships in EF 6. Here (domain classes) in Entity Framework 6.x using the code-first approach. the one-to-many relationship in the above entities, the database tables for one-to-one relationship in code first.
In a one-to-many relationship, the foreign key is defined on the table that represents the many end of the relationship. The many-to-many relationship involves defining a third table called a junction or join tablewhose primary key is composed of the foreign keys from both related tables. In a one-to-one relationship, the primary key acts additionally as a foreign key and there is no separate foreign key column for either table.
The following image shows two tables that participate in one-to-many relationship. The Course table is the dependent table because it contains the DepartmentID column that links it to the Department table.
Configuring Entity Relationships with Entity Framework
In Entity Framework, an entity can be related to other entities through an association or relationship. Each relationship contains two ends that describe the entity type and the multiplicity of the type one, zero-or-one, or many for the two entities in that relationship. The relationship may be governed by a referential constraint, which describes which end in the relationship is a principal role and which is a dependent role.
Navigation properties provide a way to navigate an association between two entity types. Every object can have a navigation property for every relationship in which it participates. Navigation properties allow you to navigate and manage relationships in both directions, returning either a reference object if the multiplicity is either one or zero-or-one or a collection if the multiplicity is many.
You may also choose to have one-way navigation, in which case you define the navigation property on only one of the types that participates in the relationship and not on both.
It is recommended to include properties in the model that map to foreign keys in the database. With foreign key properties included, you can create or change a relationship by modifying the foreign key value on a dependent object. This kind of association is called a foreign key association. Using foreign keys is even more essential when working with disconnected entities.
Note, that when working with 1-to-1 or 1-to When foreign key columns are not included in the model, the association information is managed as an independent object. Relationships are tracked through object references instead of foreign key properties. This type of association is called an independent association.
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.
Consider the following Student and Grade entity classes. First, we need to start configuring with any one entity class. CurrentGrade specifies that the Student entity has required the CurrentGrade property. This will create a NotNull foreign key column in the DB. Now, it's time to configure the other end of the relationship - the Grade entity. Students specifies that the Grade entity class includes many Student entities.
Here, many infers the ICollection type property. Now, if the Student entity does not follow the Id property convention for foreign key, then we can specify the name of the foreign key using the HasForeignKey method.
CurrentGradeId ; specifies the foreign key property in the Student entity. On this dialog you can select all items from the database that you want to be modeled. For this demo, we'll be using all Tables and Stored Procedures in the Northwind database. That's a lot of dialogs, but hey, this is the last step. Click Finish to generate your model.
Creating a Database-First Model in Entity Framework - Exception Not Found
Once the code generation is complete, you'll see a new EDMX file in your project: Open that file to see a database diagram. Mine looks like this: Well now, that looks like a well-formed database. But, what are those other files besides the EDMX?C# Entity Framework 6 - Database First - Part 1 - Basic CRUD
Let's break them down. The objects modeled by my Northwind. But what does one of those classes actually look like?
Exception Not Found
Here's the Category class: Further, it appears to have created a virtual property for Products. But what does that mean?
Types of Relationships In relational databases, tables are related to each other via the use of keys. One table has a "foreign key" to another table, and the kind of relationship tells you something about how objects in each of those tables are related. For example, in our Northwind database we have the tables Region and Territory.