Entity Framework Core - Error when trying to Add Migration after creating Model from existing database

Question

I have .NET Core Project with Entity Framework Core. I created a model from an existing database using the following command

Scaffold-DbContext "Server=.\SQLEXPRESS;Database=DBName;Trusted_Connection=True;" Microsoft.EntityFrameworkCore.SqlServer -OutputDir Models

The Model was generated and I tried to add migration but the migration that is generated is actually trying to create anew the already existing tables in the database. So when I try to run Update-Database I naturally run into the following error

Applying migration '20200912095755_SetMaxLengthToBookTitle'. Failed executing DbCommand (20ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] CREATE TABLE [Authors] ( [Id] int NOT NULL IDENTITY, [Name] nvarchar(max) NULL, CONSTRAINT [PK_Authors] PRIMARY KEY ([Id]) ); Microsoft.Data.SqlClient.SqlException (0x80131904): There is already an object named 'Authors' in the database. at Microsoft.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action1 wrapCloseInAction) at Microsoft.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action1 wrapCloseInAction) at Microsoft.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose) at Microsoft.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady)

What is the reason for that and what is the correct way to update database after creating the model from an already existing database in EF Core?

It's either code first (with migrations) or DB first (with code generated from tables), you have to pick one — Camilo Terevinto
Yes, but with Entity Framework it was possible to do code first with an existing DB. Is this not possible with Entity Framework Core? — slavhadz
Roll-back your model change so it is as originally scaffolded. Delete all of your migrations, then create a fresh initial migration e.g. dotnet ef migrations add InitialCreate. Then make your model change, and create a second migration. Remove the first migration, and see if EF will apply the second migration. May take some experimenting. — Michael

slavhadz slavhadz · Accepted Answer · 2020-09-12T17:49:38

Basically the answer that I found for myself is that I have to add an Initial migration and delete everything in it to make an empty migration. From then on I can proceed by using the code first approach as with the option 'Code first from database' that was available in EF 6.

Entity Framework Core - Error when trying to Add Migration after creating Model from existing database

1 Answers