转换类型c#
本文关键字:类型 转换 | 更新日期: 2023-09-27 18:17:03
我使用以下方法有困难:
public override List<Team> Search(Dictionary<string, string> prms,
int pageSize, int page, out int results)
{
List<Team> t = null;
//Team t = null;
var tresults = new List<Team>();
using (SqlConnection conn = DB.GetSqlConnection())
{
using (SqlCommand cmd = conn.CreateCommand())
{
cmd.CommandText = @"SearchForTeam";
cmd.CommandType = System.Data.CommandType.StoredProcedure;
foreach (var key in prms.Keys)
{
cmd.Parameters.Add(key, prms[key]);
}
SqlDataReader reader
= cmd.ExecuteReader(CommandBehavior.CloseConnection);
while (reader.Read())
{
var temp = Load(reader);
if (t == null)
{
t = temp;
}
else
{
t.CityHistory.Add(temp.CityHistory[0]);
}
}
}
}
results = 0;
return t;
}
错误主要在于if和else语句,其中if块中的temp声明它"不能隐式转换类型DataLayer"。Team to System.Collections.GenericList"
编辑:下面是我的加载方法:
public Team Load(SqlDataReader reader)
{
var team = new Team()
{
TeamID = Int32.Parse(reader["TeamID"].ToString()),
TeamName = reader["TeamName"].ToString()
};
team.CityHistory.Add(
new TeamCity(
Int32.Parse(reader["TeamCitiesID"].ToString()),
team.TeamID,
Int32.Parse(reader["CityID"].ToString()),
reader["CityName"].ToString(),
Int32.Parse(reader["YearStart"].ToString()),
Int32.Parse(reader["YearEnd"].ToString())
)
);
return team;
}
t
定义为List<Team>
,但您后来却说为t.CityHistory
。CityHistory显然不是List<>
的财产。我猜这是Team
的一个属性,但既然你从来没有告诉我们,我们不能说。
告诉我们Team
的定义和Load()
的方法签名,也许我们能给出答案。
UPDATE (from OP's UPDATE)
现在,我将假设您将获得多行,每个城市一行,团队信息重复。你想要的是:
var temp = Load(reader);
// remove t definition above
var t = tresults.FirstOrDefault(team=> team.TeamId == temp.TeamId);
if (t == null)
{
t = temp;
tresults.Add(t);
}
else
t.CityHistory.Add(temp.CityHistory[0]);
(根据Steve的评论再次更新)
您必须首先将temp
包装到List中以将其分配给t
:
if (t == null) {
t = new List<Team>() { temp }
} else {
t.add(temp);
}
很长的评论:
考虑对你的方法进行如下重构:
private IEnumerable<Team> LoadTeams()
{
using (SqlConnection conn = DB.GetSqlConnection())
{
using (SqlCommand cmd = conn.CreateCommand())
{
cmd.CommandText = @"SearchForTeam";
cmd.CommandType = System.Data.CommandType.StoredProcedure;
foreach (var key in prms.Keys)
{
cmd.Parameters.Add(key, prms[key]);
}
SqlDataReader reader
= cmd.ExecuteReader(CommandBehavior.CloseConnection);
while (reader.Read())
{
yield return Load(reader);
}
}
}
}
public override List<Team> Search(Dictionary<string, string> prms,
int pageSize, int page, out int results)
{
List<Team> searchResult = new List<Team>;
//Team t = null;
var tresults = new List<Team>();
foreach(Team team in LoadTeams())
{
if (team .....)
searchResult.Add(team);
}
results = 0;
return searchResult;
}
考虑需要初始化:
List<Team> searchResult = new List<Team>;
并问自己:下面的摘录应该做什么?:
if (team .....)
searchResult.Add(team);
注::
results = 0;
应该看起来像:
results = searchResult.Count;
我不得不在这里猜测一点,但我假设您的Load()方法返回数据类型'DataLayer '。Team',听起来像是一个Team,而你试图将它分配给't',这是一个团队列表。
试题:
t.Add(temp)
或
t.Add(temp as Team).
你总是使用'var'声明是没有帮助的。