Error when trying to share DB Context through and migrate

Question

I am starting to lean asp.net core 3 and I have an issue at present. I am trying to share my db context like I used to through a .net core dll but I have an error.

I have the following declared in my class.

// This method gets called by the runtime. Use this method to add services to e container.
public void ConfigureServices(IServiceCollection services)
{
    services.AddControllersWithViews();
    services.AddDbContext<DbContext_Model>(options =>
    options.UseSqlServer(Configuration.GetConnectionString("AppliedContext")));
}

The db context which I have in my core dll project solution.

public class DbContext_Model: DbContext
{
    public DbContext_Model(DbContextOptions<DbContext_Model> options)
      : base(options)
    { }

    public DbSet<Customer> Customer { get; set; }
    public DbSet<Policys> Policys { get; set; }

}

I have declared my connection string below with password masked

"ConnectionStrings": { "AppliedContext": "Server=DESKTOP\MSSQLSERVER2017;Database=Systems;User Id=sa;Password=xxxxx;MultipleActiveResultSets=true"

But When I do Add-Migration InitalCreate I get this error.

Unable to create an object of type 'DbContext_Model'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728

Is sharing of the context no longer allowed between .net core libarys and a web site ?

Edit 2

Please see screen shot which shows I am selecting the correct project.

Edit 3

That seemed to cause an another error the suggestion below. So I added the nugets in for the json tooling but still get this error.

dotnet ef migrations add InitialCreate System.MissingMethodException: Method not found: 'System.Text.Json.JsonDocument System.Text.Json.JsonDocument.Parse(System.IO.Stream, System.Text.Json.JsonReaderOptions)'. at Microsoft.EntityFrameworkCore.Tools.RootCommand.Execute() at Microsoft.EntityFrameworkCore.Tools.Commands.CommandBase.<>c__DisplayClass0_0.b__0() at Microsoft.DotNet.Cli.CommandLine.CommandLineApplication.Execute(String[] args) at Microsoft.EntityFrameworkCore.Tools.Program.Main(String[] args) Method not found: 'System.Text.Json.JsonDocument System.Text.Json.JsonDocument.Parse(System.IO.Stream, System.Text.Json.JsonReaderOptions)'. PM> dotnet ef migrations add InitialCreate

You’re probably trying to create the migrations with the wrong project. You will have to use the one that actually _configures_ the context. Otherwise, the migration tool won’t be able to construct it. At least if you want to configure it that way. — poke, Aug 29 '19 at 22:36
Hi Please see screen shot that i am selecting the shared libary — c-sharp-and-swiftui-devni, Aug 29 '19 at 22:55

score 0 · Answer 1 · answered Aug 29 '19 at 22:57

0

Try something like this:

options.UseSqlServer(
    Configuration.GetConnectionString("AppliedContext"),
    options => options.MigrationsAssembly(<DB_PROJECT>)

Then you should be able to run this from within the folder that has the DbContext project:

dotnet ef migrations add <NAME> --startup-project <STARTUP_PROJECT>

answered Aug 29 '19 at 22:57

crgolden

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Oh ok - I didn't know you were using 3.0. Try this: https://stackoverflow.com/a/56487123 – crgolden Aug 29 '19 at 23:22
Try running `dotnet tool install --global dotnet-ef --version 3.0.0-*` to update your `dotnet ef` tools then. – poke Aug 30 '19 at 05:14

score 0 · Answer 2 · answered Aug 30 '19 at 07:03

From the screenshot in your Edit3, your need to update EF Core related package to version 3.0 . In Manage NutGet Packages , check Include prerelease next to the search box and update them to latest version like below :

<PropertyGroup>
<TargetFramework>netcoreapp3.0</TargetFramework>
</PropertyGroup>

<ItemGroup>
  <PackageReference Include="Microsoft.EntityFrameworkCore" Version="3.0.0-preview8.19405.11" />
  <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="3.0.0-preview8.19405.11">
    <PrivateAssets>all</PrivateAssets>
    <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
  </PackageReference>
  <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="3.0.0-preview8.19405.11" />
  <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="3.0.0-preview8.19405.11">
    <PrivateAssets>all</PrivateAssets>
    <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
  </PackageReference>
</ItemGroup>

</Project>

Note :When adding migration , set your web application as the Startup project and set the class library as the default project where you want Migration folder generates.

Reference :https://dotnetthoughts.net/using-ef-core-in-a-separate-class-library/

Dejan · Answer 3 · 2019-09-01T15:21:40.890

The screenshot of your Edit3 seems to indicate that your EF tool version is outdated. You can check by executing:

dotnet ef --version

on the command line. If it's not preview8, then install it:

dotnet tool update dotnet-ef --version 3.0.0-preview8.19405.11

(optionally use the --global switch).

Beware: EF preview8 has an additional issue when used with HasData. It should be fixed in preview9 (which at the time of this writing is not out yet).

Error when trying to share DB Context through and migrate

3 Answers3