Lifetime

The lifetime of DbContext begins when the instance is created and ends when it is disposed. It lasts for a unit of work.

A unit of work keeps track of everything you do during a business transaction that can affect the database. When you’re done, it figures out everything that needs to be done to alter the database as a result of the work."

Threading and Concurrency

DbContext is not thread-safe. This includes parallel execution of async queries and any explicit concurrent use from multiple threads. Always await async calls immediately.

Concurrent access detection

EF Core detects attempts to use a DbContext instance concurrently and throws an InvalidOperationException. Undetected attempts result in undefined behavior, crashes, and data corruption.

Error Handling

An InvalidOperationException thrown by EF Core puts the context into an unrecoverable state. The context must be discarded at this point.

Creating & Configuring a DbContext

Create a subclass of DbContext:

SomeDbContext.cs

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

Register the DbContext in DI

Each DbContext instance must be configured to use exactly one database provider: Program.cs

using Microsoft.EntityFrameworkCore;

builder.Services.AddDbContext<EmployeeManagerDbContext>(
    opt => 
        opt.UseSqlServer(builder.Configuration.GetConnectionString("EmployeeManagerDb")));

Database-provider specific configuration is performed in a provider-specific options builder:

builder.Services.AddDbContext<EmployeeManagerDbContext>(
    opt => 
        opt.UseSqlServer(
            builder.Configuration.GetConnectionString("EmployeeManagerDb"),
            providerOptions => { providerOptions.EnableRetryOnFailure() } ));

Other DbContext Configuration Notes

DbContextOptions<T> vs DbContextOptions

• DbContext subclasses that accept a DbContextOptions must use DbContextOptions<T> to ensure the correct options for that DbContext subtype are resolved from DI.
• If the DbContext subtype itself is intended to be inherited, use the DbContextOptions.

DbContextOptionsBuilder methods

DbContextOptionsBuilder has other common methods for configuring the DbContext:

Using DbContext

Inject the DbContext into the desired code via dependency injection:

public class SomeController
{
    private readonly SomeDbContext _context;

    public SomeController(SomeDbContext context) 
    {
        _context = context;
    }
}