![]() Map(m => m.ToTable( "StudentCourse").MapLeftKey( "CourseId"). Protected override void OnModelCreating(DbModelBuilder modelBuilder) Complex index that spans two fields and adds another three as include columns Not a problem in Fluent but no way to do it in DataAnnotations (Infact Indexes in general got ripped out of attributes and are only just now making their way back in with a much weaker configuration than just using Fluent https. Public partial class SchoolContext : DbContext The thing is, Fluent Configurations are much more powerful than Data Annotations. This will generate all the entity classes for your DB tables and views as shown below.įor example, it will create the following context class which uses Fluent API to configure entity classes as per your database. Now, choose the tables and views for which you want to generate classes and click on Finish. So know we have a T4 template, that generates entities with support for WPF validation using data annotations and the buddy mechanism. Create a new connection for your database if the dropdown does not include the connection to your existing database. Now, select the data connection for the existing database. Select Code First from database option and click Next. This will open the Entity Data Model wizard as shown below. Select ADO.NET Entity Data Model in the Add New Item dialog box and specify the model name (this will be a context class name) and click on Add. The following table lists options for aspnet-codegenerator razorpage, controller and view: Option Description-model or -m: Model class to use.-dataContext or -dc: The DbContext class to use or the name of the class to generate.-bootstrapVersion or -b: Specifies the bootstrap version. If you already have scaffolding and want to override existing files with new scaffolding (generated using new or updated schema) please use the below command. To use code-first for an existing database, right click on your project in Visual Studio -> Add -> New Item. dotnet ef dbcontext scaffold -output-dir EmployeeContextModels. It will create entity classes for all the tables & views in your existing database and configure them with data annotations attributes and Fluent API. Here, you will learn how to generate context and entity classes for an existing database, using the code-first approach.Įntity Framework provides an easy way to use the code-first approach for an existing database. ![]() using Microsoft.Next Generate Context and Entity Classes from an Existing Database in EF 6 Code-First Approach ![]() If you are using EF Core 5, you can use Data Annotation attribute to indicate that the entity doesn't need a primary key. protected override void OnModelCreating(ModelBuilder modelBuilder) If you don't want a primary key for the entity, add the following code inside OnModelCreating method of your DbContext class. Here, the key attribute is used to mention the primary key property name. If you want a field with a custom name as the primary key, the following solution will work. Here, when you have an entity with a property named Id, EF Core accepts that property as the primary key by EF Core conventions. The error will disappear when the entity class is modified as follows. Its caused by a specific Data Seeding (HasData) requirement. The same happens for any autogenerated key values, including the commonly used auto increment (identity) columns. You can configure any property to have its value generated for inserted entities as follows: Data Annotations. Obviously, the first solution is defining a primary key for the entity.ĭefine a primary key. The problem you are experiencing is not specific for autogenerated Guids. Scaffold-Dbcontext with Data Annotations. We saw above that EF Core automatically sets up value generation for primary keys - but we may want to do the same for non-key properties. I have edited the nearly useless (for Winforms) EF5 DBContext Generator template, implementing IDataErrorInfo. If the entity is a keyless entity, we have to specify it explicitly in OnModelCreating method. You will note, perhaps, that I was asking if the DataGridView can communicate with whatever interfaces are implemented by EF5 DbContext. The entity requires a primary key to be defined. Updating the Model The recommended approach to keeping changes to the database in sync with the generated model is to use migrations i.e. For more information on keyless entity types, Since Data Annotations only cover a subset of configuration options, you are likely to find that the Fluent API has also been used to configure the model. If you intended to use a keyless entity type,Ĭall 'HasNoKey' in 'OnModelCreating'. } The entity type 'Student' requires a primary key to be defined. I got the following error when I ran the add-migration command for the following entity.
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