System.InvalidCastException occurred in EntityFramework.Core.dll

The below is the the Application Entity:

public class Application
{
    [Key]
    [Column(TypeName = "integer")]
    public int ApplicationID { get; set; }

    [Required]
    [Column(TypeName = "nvarchar(50)")]
    public string ApplicationName { get; set; }

    [Column(TypeName = "nvarchar(150)")]
    public string Description { get; set; }

    [Required]
    [ForeignKey("mTechnology")]
    [Column(TypeName = "integer")]
    public int TechnologyID { get; set; }

    [Required]
    [Column(TypeName = "int")]
    public string CreatedBy { get; set; }

    [Required]
    [Column(TypeName = "datetime")]
    public DateTime CreatedDate { get; set; }

    public virtual mTechnology Technology { get; set; }
}

On executing the below LINQ query, I am getting an error at run-time in the foreach loop

List<int> technologyList = new List<int>();
var query = from a in _mApplicationDbContext.Applications
        group a.Technology by a.TechnologyID into g
        select new
        {
            TechnologyID = g.Key
        };

foreach (var item in query)
{
    technologyList.Add(item.TechnologyID);
}

The below is the error message:

An exception of type 'System.InvalidCastException' occurred in EntityFramework.Core.dll but was not handled in user code

Additional information: Unable to cast object of type 'System.Int32' to type 'System.String'.

Is the LINQ query wrong or any other error?