c# – 使用未知数量的参数查询数据库

我正在尝试查询现有的访问数据库,并允许用户为WHERE子句选择多个值.我一直在使用此网站上的代码由用户Mark Brackett提供：

string[] tags = new string[] { "ruby","rails","scruffy","rubyonrails" };
string cmdText = "SELECT * FROM Tags WHERE Name IN ({0})";

string[] paramNames = tags.Select(
    (s,i) => "@tag" + i.ToString()
).ToArray();

string inClause = string.Join(",",paramNames);
using (sqlCommand cmd = new sqlCommand(string.Format(cmdText,inClause))) {
    for(int i = 0; i < paramNames.Length; i++) {
       cmd.Parameters.AddWithValue(paramNames[i],tags[i]);
    }
}

这给了这个：

cmd.CommandText = "SELECT * FROM Tags WHERE Name IN (@tag0,@tag1,@tag2,@tag3)"
cmd.Parameters["@tag0"] = "ruby"
cmd.Parameters["@tag1"] = "rails"
cmd.Parameters["@tag2"] = "scruffy"
cmd.Parameters["@tag3"] = "rubyonrails"

这非常有效,但我也想要以下功能.如果用户决定不输入任何值(在此示例中,如果tags数组为空),则我希望返回所有结果.实际上只是一个SELECT * FROM标签.

解决方法

怎么样的

string[] tags = new string[] { "ruby","rubyonrails" };
string cmdText = "SELECT * FROM Tags {0}";

string[] paramNames = tags.Select(
            (s,i) => "@tag" + i.ToString()
        ).ToArray();

string cmdWhere = paramNames.Length > 0 ? String.Format("WHERE Name IN ({0})",string.Join(",paramNames)) : "";
using (sqlCommand cmd = new sqlCommand(string.Format(cmdText,cmdWhere)))
{
    for (int i = 0; i < paramNames.Length; i++)
    {
        cmd.Parameters.AddWithValue(paramNames[i],tags[i]);
    }
}

因此,如果没有参数,则最后不添加where子句.