Disable the default constructor on a Database-First workflow - entity-framework

Question

How can I prevent the use of the parameterless constructor of the generated DbContext?
var dcx = new DataEntities();
The default constructor is generated by the T4 template, and I thus cannot override it in a partial class. I would prefer it not compile, but a runtime error would also be good.

Answer 1

You can modify the template to provide the constructor you want.
Open the *.Context.tt file
Go to line ~59
Change this code.
public <#=code.Escape(container)#>()
: base("name=<#=container.Name#>")
Into the default constructor you want, for example.
public <#=code.Escape(container)#>(string nameOrConnectionString)
: base(nameOrConnectionString)
Save

Answer 2

You can inherit the DbContext created by the template, define your own constructor, and use the inherited DbContext instead of the one generated by the template.
public class MyModifiedDbContext : TheTemplateGeneratedDbContext
{
public MyModifiedDbContext()
{
// define your own constructor
}
}
Or make it private to avoid its use, so you get the error at compile time
public class MyModifiedDbContext : TheTemplateGeneratedDbContext
{
private MyModifiedDbContext()
// ...
}
Use MyModifiedDbContext instead of TheTemplateGeneratedDbContext

Answer 3

I gave up waiting for EF Core team to add this as an option. I don't want to make and maintain my own T4 templates for this - that's nuts!
Solution for me was just to run some regex on the generated code as part of a powershell script.
fix-dbcontext.ps1
$filename=$args[0]
# load context file
$content = (Get-Content -Raw $filename)
[regex] $commentOutConstructorRegex = '(?ms)(?<=: DbContext\s*.*?)(public.*?)(?=\s*public)'
$content = $commentOutConstructorRegex.Replace($content, '// Default constructor removed', 1)
[regex] $removeOnConfiguringRegex = '(?ms)(protected override void OnConfiguring).*?(?=\s*protected)'
$content = $removeOnConfiguringRegex.Replace($content, '// Generated OnConfiguring removed', 1)
[regex] $dateCommentRegex = '(?ms)(?=\s*public partial class)'
$content = $dateCommentRegex.Replace($content, "`r`n`t// Generated " + (Get-Date).ToString() + "`r`n", 1)
$content | Out-File -Encoding UTF8 $filename
This will:
Remove the default constructor
Remove the OnConfiguring method including hardcoded connection string
Add the date in a comment
Just run it with .\fix-dbcontext.ps1 .\MyDBContext.cs.
You probably want to change that last line to context.txt instead of $filename until you're sure it does what you want.
IMPORTANT: This was tested only on EFCore templates, but if you understand my Regexes you should be able to modify it for EntityFramework if it doesn't already work.