Entity Framework Database First .Net Core

问题

I have a .Net Standard 2.0 class library project and I want to add Entity Framework to it. I have added the Entity Framework Core package to the project but no Entity Framework Templates appear when I try to add a new item to the project. I have looked on the web and all I can seem to find is instructions for Code First!

How do I get the database first functionality back?

回答1:

EF Core does not, and will never, support the EDMX-based Database First workflow with the designer. EF Core stores all object-to-database mapping in Attributes and Fluent API mapping in your source code.

In EF 6 the term "Code First" meant two very different things. One is a code-first modeling workflow where your database was generated from your .NET classes. The other meaning of "Code First" was just that the mapping metadata was embedded in your source code (Attributes/Fluent API) rather than in an EDMX file. EF 6 supported two different database-first workflows. Database-first with the EDMX, and the workflow officially called "Code First From an Existing Database", but which could have been called "Database-First with Code-Based Mapping".

In EF Core, your code will always have the mapping, and so in that sense it's "code first". But you can still do a database-first design workflow, and write entities and mapping code that match your existing database.

And you can use the scaffold-dbcontext in the Package Manager Console, or dotnet ef dbcontext scaffold in the CLI command to generate entity classes and mapping metadata from an existing database. See Getting Started with EF Core on ASP.NET Core with an Existing Database

回答2:

In ".net core", you can not use EF from the menu and the "add a new item" button.

Make sure the "Microsoft.VisualStudio.Web.CodeGeneration.Design" package is installed:

1. Goto Tools –> NuGet Package Manager –> Package Manager Console

2. Run Install-Package Microsoft.VisualStudio.Web.CodeGeneration.Design

Then follow these steps:

1. Create a connection string by the sample code. (SQLSERVER,DATABASE,USERNAME,PASS)

   Data Source=SQLSERVER;Initial Catalog=DATABASE;persist security info=True;user id=USERNAME;password=PASS

2. Edit the sample code and place the code above in the quotation. (CONECTIONSTRING,FOLDERNAME)

   Scaffold-DbContext "CONECTIONSTRING" Microsoft.EntityFrameworkCore.SqlServer -OutputDir FOLDERNAME

3. For example, this is the result of steps 1 and 2.

   Scaffold-DbContext "Data Source=localhost;Initial Catalog=myDb;persist security info=True;user id=sa;password=0000" Microsoft.EntityFrameworkCore.SqlServer -OutputDir Models/EF

4. Run the code above through the Tools –> NuGet Package Manager –> Package Manager Console

More details on the Getting Started with EF Core on ASP.NET Core with an Existing Database

来源：https://stackoverflow.com/questions/48552258/entity-framework-database-first-net-core