repository pattern on asp core - asp.net

Question

we are trying to develop a asp core application (MVC) using ef code first . however it seems that requires the db context to be in an executable and not class library .
so the data context was added in the web UI project but the issue that how can the db context's dbset be made available in the repository project ..
example code is as under:
public class CompanyRepository : GenericRepository<Company>, /*IGenericRepository<Company>*/ ICompanyRepository
{
public CompanyRepository(DbContext dbContext) : base(dbContext)
{
}
public async Task<IEnumerable<Company>> GetAllAsync()
{
return await base.GetAllAsync<Company>();
}
}
MVC Project StartUp .cs
services.AddDbContext<DBContext>();
services.AddScoped<ICompanyRepository, CompanyRepository>();
DBCOntext.cs in MVC Project
public class DBContext : DbContext
{
private IConfigurationRoot _config;
public DBContext(IConfigurationRoot config, DbContextOptions options):base(options)
{
_config = config;
}
}
currently it seems to raise following error:
An unhandled exception occurred while processing the request. InvalidOperationException: Unable to resolve
service for type 'Microsoft.EntityFrameworkCore.DbContext' while
attempting to activate
'On.Store.Repository.Companies.CompanyRepository'.

Answer 1

We have two problems here:
1) When you configure services in a Startup class, you are configuring your custom context (for easier reference, let's name it CustomDbContext):
public class CustomDbContext: DbContext
{
... and in the Startup class:
services.AddDbContext<CustomDbContext>();
... so in your repository, you need to inject a context of declared class, instead of base DbContext class:
// THIS WILL NOT WORK
public class CompanyRepository : GenericRepository<Company>, ICompanyRepository
{
public CompanyRepository(DbContext dbContext) : base(dbContext)
{
}
}
// THIS WILL WORK
public class CompanyRepository : GenericRepository<Company>, ICompanyRepository
{
public CompanyRepository(CustomDbContext dbContext) : base(dbContext)
{
}
}
2) Problem number two is revealed directly from the first problem. So you have CustomDbContext declared in a MVC project, so cannot be used in a referenced repository project. So the solution seems to be easy, you need to move the CustomDbContext out of the MVC project (either to repository project or any other/third project which could be referenced by both MVC and repository). In such way you will easy configure your CustomDbContext in a Startup class, as well as use this context in repositories.
3) As it comes to registering context from external library you can do it easily with MigrationsAssembly method, it will look like this:
services.AddDbContext<CustomDbContext>(options => options.UseSqlServer(
_configuration.GetConnectionString("YourConnectionStringName"),
b => b.MigrationsAssembly("YourExternalAssemblyName")));

Answer 2

This is an very simples project that can help you and other developers.
Generic Repository Pattern in ASP.NET Core

Answer 3

This is addressing your orginal issue of being unable to use migration command line tools and allow you to keep proper separation of layers.
This is a know issue (tracked here) and there are two workarounds as of now, directly taken from the EntityFramework Core documentation:
Workaround 1 - Utilize a separate startup project
Convert the class library project into an “app” project. This can either be a .NET Core app or a desktop .NET app.
Example:
{
"frameworks": {
"netcoreapp1.0": {
"dependencies": {
"Microsoft.NETCore.App": {
"type": "platform",
"version": "1.0.0-*"
}
}
}
}
}
Be sure to register the EntityFramework Tools as a project dependency and in the tools section of your project.json.
Example:
{
"dependencies": {
"Microsoft.EntityFrameworkCore.Tools": {
"version": "1.0.0-preview2-final",
"type": "build"
}
},
"tools": {
"Microsoft.EntityFrameworkCore.Tools": "1.0.0-preview2-final"
}
}
Finally, specify a startup project that is a “runnable app.”
Example:
dotnet ef --startup-project ../MyConsoleApplication/ migrations list
Workaround 2 - Modify your class library to be a startup application
Convert the class library project into an “app” project. This can either be a .NET Core app or a desktop .NET app.
To make the project a .NET Core App, add the “netcoreapp1.0” framework to project.json along with the other settings in the sample below:
{
"buildOptions": {
"emitEntryPoint": true
},
"frameworks": {
"netcoreapp1.0": {
"dependencies": {
"Microsoft.NETCore.App": {
"type": "platform",
"version": "1.0.0-*"
}
}
}
}
}
To make a desktop .NET app, ensure you project targets “net451” or newer (example “net461” also works) and ensure the build option "emitEntryPoint" is set to true.
{
"buildOptions": {
"emitEntryPoint": true
},
"frameworks": {
"net451": { }
}
}