從SQL Server 2012 Express檢索數據時出現“ System.InvalidCastException”錯誤

Question

我正在嘗試測試一種從SQL Server 2012 Express實例檢索一些信息並將其“添加”到列表中的方法。 問題是當我嘗試運行測試時出現錯誤：

“ System.InvalidCastException”

這是代碼：

List<Reference> lst = new List<Reference>();
//DB Connections is a class instance that takes care of the
//connection with the db.
DBConnections db = new DBConnections(DbConfig.conStr);
db.UpdateCmd("SELECT * FROM freelancers_references");

SqlDataReader dr = db.ExecuteReader();

if (dr.HasRows) {
    lst = dr.Cast<IDataRecord>().Select(r =>
        new Reference {
            Id = (int)dr["id"],
            OwnerId = (int)dr["owner_id"],
            Name = (string)dr["name"],
            Active = (bool)dr["active"]
        }).ToList<Reference>();
}

dr.Close();
return lst;   

編輯：@丹提供了一個有效的答案。 盡管使用Convert.ToInt / ToString（）等方法也能達到目的。

Answer 1

檢查列是否允許為空。 如果是這樣，則將類型設置為可為空

OwnerId = (int?)dr["owner_id"],

Answer 2

DBConnections db = new DBConnections(DbConfig.conStr);
db.UpdateCmd("SELECT * FROM freelancers_references");
SqlDataReader dr = db.ExecuteReader();
if (dr.HasRows) {
    lst = dr.OfType<IDataRecord>().Select(r =>
        new Reference {
            Id = (int)dr["id"],
            OwnerId = (int)dr["owner_id"],
            Name = (string)dr["name"],
            Active = (bool)dr["active"]
        }).ToList();
}
dr.Close();