03_DbContext - Maniconserve/EF-Core GitHub Wiki

• The DbContext class is part of the Microsoft.EntityFrameworkCore package.
• It acts as a bridge between the database and the application.
• It manages database operations like querying, inserting, updating, and deleting records.

Common Methods in DbContext

Add(entity) – Adds a new record to the database.

AddRange(entities) – Adds multiple records at once.

Find(key) – Retrieves an entity by primary key.

FirstOrDefault() – Returns the first matching record or null if none found.

Update(entity) – Updates an existing record.

Remove(entity) – Deletes a record from the database.

SaveChanges() – Commits all changes to the database.

SaveChangesAsync() – Asynchronously commits changes to the database.

Set() – Gets the DbSet for a specific entity type.

Entry(entity) – Provides access to entity tracking information.

1. Constructor Injection in DbContext

• Uses dependency injection to provide the DbContextOptions at runtime.
• Recommended for ASP.NET Core applications to manage the DbContext through DI container.

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

    public DbSet<Employee> Employees { get; set; }  
}

• The DbContext is registered in Program.cs:

builder.Services.AddDbContext<ApplicationDbContext>(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection")));

2. OnConfiguring Method in DbContext

• Used when dependency injection is not available.
• Manually configures the database connection inside DbContext.

public class ApplicationDbContext : DbContext  
{  
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)  
    {  
        optionsBuilder.UseSqlServer("Server=.;Database=MyDB;Trusted_Connection=True;");  
    }  

    public DbSet<Employee> Employees { get; set; }  
}

• This method directly sets the connection string, useful in small applications or console applications without dependency injection.