Tag: CodeFirst

Sequence contains more than one element

Easiest way to debug Seed-method in Code-first migrations in Entity Framework

This post describes the easiest way to debug the issues that may stop your Seed-method in Configuration.cs from going through. This problem concerns typically your ASP.NET MVC projects, either on .NET Framework or .NET Core – the same basic idea should work for both situations. The solution here shows you, how you can get a little bit more information out of the process, without attaching the debugger (there’s another blog post for that: How to launch the visual studio debugger from code/) Description Entity Framework’s […]

Applying Entity Framework’s Code-First Migrations against a Database in Azure by running Update-Database

This post describes how to run Entity Framework’s code-first migrations against a database located in the Windows Azure. This is done by running Update-Database commandlet with suitable switches, see below. The problem and symptoms Okay, so you’re developing your MVC+EF cool web app with a database in Azure, and you’re using code-first migrations. Cool! What’s nice with code-first-migrations is the fact they are run automatically even in the cloud the next time your app is running (as long as you publish your app with that […]

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Fixing the error: “Column XX in table dbo.YY is of a type that is invalid for use as a key column in an index.”

While using Entity Framework and code-first migrations, Entity Framework (EF) creates the indexes for you – but what if you need to create a custom one, explicitly based on certain field / column? Then you’ll have to tell EF which one to use as a key column. Usually, it’s easy – you just add the following annotation to the columns you’ll be using: [Index(“OfficialIds”, 1)] public int AreaId { get; set; } [Index(“OfficialIds”, 2)] public string EstateId { get; set; } (example stripped of extra code and other columns for clarity) And after adding the migration (Add-Migration… commandlet) you get […]

Entity Framework's Update-Database throwing an error

Fixing “An error occurred while updating the entries” while running code-first migrations in MVC 5 app

This post describes an issue with EF’s code-first migrations, when mapping between DB’s DateTime (datetime2) and C#’s DateTime simply fails, and results in the Update-Database cmdlet failing, too. It’s more or less a prime example of a situation, where the error itself tells very little about the actual issue, and since debugging code-first migrations is kind of difficult (see the best tips for that here!), it’s cumbersome to investigate. Symptoms So what’s the error that we’re running into, exactly? Below, you can find the most […]