ASP/Entity：数据库每次都为空

Question

在 if 语句的末尾，busAddr 始终是“不存在此类型的地址...”

为什么会这样？

int counter = 0;
string queryID = "";
List<string> busAddr = new List<string>();
while (counter != busIDs.Count)
{
    queryID = busIDs[counter];
    var gathered = (from c in db.tblbus_address where c.BusinessID == queryID && c.AddressTypeID == addrnum select c);
    var address = gathered as tblbus_address;
    var all = address.Address1;
    if (address != null && !string.IsNullOrEmpty(all[counter].ToString()))
    {
        string test = address.Address1[counter].ToString();
        busAddr.Add(test);
    }
    else
    {
        busAddr.Add("No address for this type exists...");
    }
    counter++;
}

Answer 1

看看这一行

var gathered = (from c in db.tblbus_address where c.BusinessID == queryID && c.AddressTypeID == addrnum select c);

这将返回一个可查询的。数据库查询此时尚未完成。所以你需要以某种方式触发它，通过调用“ToList”、“First”或类似的实际请求值的东西。

现在来了

var address = gathered as tblbus_address;

您正在将此可查询对象转换为项目类型。当然这个演员表是无效的，所以这行结果是null。

要解决此问题，请强制执行数据库查询并确保您投射正确的内容。例如：

var gathered = (from c in db.tblbus_address where c.BusinessID == queryID && c.AddressTypeID == addrnum select c).ToList();
var address = gathered[0] as tblbus_address;

或者

var gathered = (from c in db.tblbus_address where c.BusinessID == queryID && c.AddressTypeID == addrnum select c);
var address = gathered.First() as tblbus_address;

并记得处理边缘情况，例如找不到项目。