Entity Framework in Depth | Code with Mosh
Entity Framework 6 in Depth Understand the differences between code-first and database-first workflows; Build a domain model using database-first workflow; Build This course is produced with Entity Framework 6. "May God bless you and your efforts to create high-quality courses. Fluent API- Relationships (). Part 1: Using Entity Framework with an existing database SQL Server databases with predefined tables and relationships. Entity Framework 6 has a number of features to make working with existing databases fairly straightforward. entities is automatically loaded from the database the first time that a. There are a small number of mistakes in database design that causes In reality, however, it is quite common that not even the first Normal Form is implemented correctly. it will also contain definitions on its tables, columns, relationships, and even default .. The one from Lord of the Rings is the best.
The generation of the EF classes and DbContext is done using some t4 templates, referred to as scaffolding. Be default it uses some internal scaffolding, but you can import the scaffolding and change it. Once you have installed the EntityFramework.
CodeTemplates you will find two files called Content. I found the word virtual in the EntityType. I also removed virtual from the Content. You may want to alter the scaffolding more extensively, say to add a [Key] attribute on primary keys for some reason.
All is possible, but you must dig into the. One warning about using importing scaffolding — Visual Studio threw a nasty error message when first tried to import using the EntityFramework. CodeTemplates scaffolding see stackoverflow entry. It took a bit of finding but it turns out if you have Entity Framework Power Tools Beta 4 installed then they clash.
I hope that gets fixed as Entity Framework Power Tools is very useful.
There are two other methods to reverse engineer an existing database: Entity Framework Power Tools Beta 4 can also reverse engineer a database. Its quicker, only two clicks, but its less controllable. This caused problems when I tried to create a new SalesOrderDetail so that I could add a line item to an order. I got the SQL error: That confused me for a bit, as other two-key items had worked, such as CustomerAddress.
The best solution would be to edited the scaffolding again to always add that attribute to identity keys. This is a generally useful feature so I use this example to show you how to do this in the next section. Adding new DataAnnotations to EF Generated classes Being able to add attributes to properties in already generated classes is a generally useful thing to do.
I needed it to fix the key problem see 1. What happens when the database changes? There are a few things you need to do before, during and after the reimport.
That way it will recompile properly without major name changes. Because you are using the same name as the existing DbContext you must delete the previous DbContext otherwise the reimporting process will fails. If its easier you can delete all the generated files as they are replaced anyway.
Configure One-to-One relationship in Code First Entity Framework
That is why I suggest you put them in a separate directory with no other files added. When reimporting by default the process will add the connection string to your App.
- One-to-One Relationship
- Your Instructor
- Configure a One-to-Zero-or-One relationship using Fluent API
I suggest you un-tick that otherwise you end up with lots of connection strings minor point, but can be confusing. To represent this, the Standard entity has the collection navigation property Teachers please notice that it's pluralwhich indicates that one Standard can have a collection of Teachers many teachers. And the Teacher entity has a Standard navigation property reference propertywhich indicates that Teacher is associated with one Standard.
This makes it a One-to-Many relationship.
Entity Framework: working with an existing database
It means one Student can enroll for many Courses and also, one Course can be taught to many Students. The database includes the StudentCourse joining table which includes the primary key of both the tables Student and Course tables. Entity Framework represents many-to-many relationships by not having the entity set DbSet property for the joining table in the CSDL and visual designer.
Instead it manages this through mapping. However, we also need to make it a foreign key which points to StudentId of the Student entity. So, apply [ForeignKey "Student" ] on the StudentAddressId property which will make it a foreign key for the Student entity, as shown below.
Student includes the StudentAddress navigation property and StudentAddress includes the Student navigation property. With the one-to-zero-or-one relationship, a Student can be saved without StudentAddress but the StudentAddress entity cannot be saved without the Student entity. EF will throw an exception if you try to save the StudentAddress entity without the Student entity. 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.