c# - 从 SqlDataReader 填充通用列表 [英] c# - Fill generic list from SqlDataReader
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问题描述
如何将 SqlDataReader
返回的值添加到通用列表?我有一种方法,我使用 SqlDataReader
从 Category
表中获取 CategoryID
.我想添加所有 CategoryID
一个通用列表.
How can I add values that a SqlDataReader
returns to a generic List? I have a method where I use SqlDataReader
to get CategoryID
from a Category
table. I would like to add all the CategoryID
a generic List.
这不起作用,因为它只返回一个 categoryID
而这是最后一个.我想将所有 categoryID
添加到列表中,然后返回它们.
This dose not work because it returns only one categoryID
and that is the last one. I want to add all the categoryID
to the list and then return them.
我该怎么做?
SqlConnection connection = null;
SqlDataReader reader = null;
SqlCommand cmd = null;
try
{
connection = new SqlConnection(connectionString);
cmd = new SqlCommand("select CategoryID from Categories", connection );
connection.Open();
List<int> catID = new List<int>();
dr = cmd.ExecuteReader();
while (dr.Read())
{
catID.Add(Convert.ToInt32(dr["CategoryID"].ToString()));
}
}
finally
{
if (connection != null)
connection.Close();
}
return catID;
推荐答案
试试这个,更好,更安全,使用延迟加载,更少的代码,工作,...:
Try like this, it's better, safer, uses lazy loading, less code, working, ...:
public IEnumerable<int> GetIds()
{
using (var connection = new SqlConnection(connectionString))
using (var cmd = connection.CreateCommand())
{
connection.Open();
cmd.CommandText = "select CategoryID from Categories";
using (var reader = cmd.ExecuteReader())
{
while (reader.Read())
{
yield return reader.GetInt32(reader.GetOrdinal("CategoryID"));
}
}
}
}
然后:
List<int> catIds = GetIds().ToList();
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