insert data from source to destination with no primary key

Once you have the data in the destinationData list, you can insert it into the destination table using the AddRange method of the DbContext class.

_dbContext.Data2.AddRange(destinationData);
_dbContext.SaveChanges();

This will insert all the data from the destinationData list into the Data2 table.

To insert data from a source to a destination table in Entity Framework Core with different column names and no primary key, you can use a combination of LINQ and mapping to achieve this. Fetch the data from the source table and map it to the destination table. 

var sourceData = _dbContext.Data.ToList();

var destinationData = sourceData.Select(s => new Data2
{
    A_Abc = s.Abc,
    A_cde = s.cde,
    A_efg = s.efg
}).ToList();

after using fluent API .HasNoKey to define the keyless entity issue is resolved but again getting another error invalid column name

source table

column name : abc,bcd,egf

destination table:

column name: A_abc,A_bcd,A_egf

Hello Meghana M ,
To define Keyless Entities in EF, there are two ways : based  in your example 
1- Use data annotation [Keyless]. Annotate a model with this attribute

[Keyless]
 public class Data
    {
        public string Abc { get; set; }
        public string cde { get; set; }
        public string efg{ get; set; }
      }

OR

2- use fluent API .HasNoKey to define the keyless entity

// DbContext
public class Data2DBcontext : DbContext
{
    public Data2DBcontext(DbContextOptions options)
        : base(options)
    {
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity()
            .HasNoKey();
    }

    public DbSet Datas { get; set; }
}

BENCHAABAN Ali