how to write api's in dotnet core and entity code example

Example: insert multiple records on the Database in Entity Framework Core

var dept1 = new Department() { Name = "Development" };
var dept2 = new Department() { Name = "HR" };
var dept3 = new Department() { Name = "Marketing" };
 
using (var context = new CompanyContext())
{
    context.Department.AddRange(dept1, dept2, dept3);
    context.SaveChanges();
}