Creating a Generic DbSet.Find() query-CodePudding

I have a database with 3 tables for classes that all implement my IMeetingEntityEntityBaseClass.cs

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

        }
        
        public DbSet<MeetingSpace> MeetingSpaces { get; set; } 
        public DbSet<Employee> Employees { get; set; } 
        public DbSet<Booking> Bookings { get; set; } 
    }

I started off with only the MeetingSpaces table and was trying to make my database operation methods generic so they could be reused for the other two tables. However they (and my ASP.NET pages) rely on the Id to identify the meeting space. My problem is that I cant figure out how to make the GetById class generic. For the MeetingSpace table query it is as follows:

public MeetingSpace GetById(int id)
        {
            return db.MeetingSpaces.Find(id);
        }

I attempted to use the Find overload with the type specified but the typeof(T) returns 'object', throwing an error that type 'object' cannot be converted to 'T'.

public T GetById<T>(int id) where T : IMeetingEntityBaseClass
        {
            return db.Find(typeof(T), id);
        }

CodePudding user response：

You need to use the DbContext.Set method. Also, you need to add a type constraint since the Set method relies in it (as do all EF entities.) For example:

public T GetById<T>(int id) 
    where T : class, IMeetingEntityBaseClass
{
    return db.Set<T>().Find(id);
}