C# 从实体中获取单列
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Getting single column from an entity
提问by Kevin Albrecht
How can you get a single column back from a query instead of a whole object?
如何从查询中获取单个列而不是整个对象？
I could do something like this to get the whole object, but all I want is the names:
我可以做这样的事情来获取整个对象，但我想要的只是名称：
IList<Tribble> tribbles = session.CreateCriteria(typeof(Tribble)).List<Tribble>();
IList<string> names = new List<string>();
foreach (Tribble t in tribbles) {
names.Add(t.Name);
}
I would like to be able to specify additional criteria, so is it possible to just exclude certain columns from being retrieved?
我希望能够指定额外的条件，那么是否可以只排除某些列不被检索？
采纳答案by Kevin Albrecht
Here is the solution I eventually ended up using:
这是我最终使用的解决方案：
ICriteria c = session.CreateCriteria(typeof(Tribble));
c.SetProjection(Projections.ProjectionList().Add(Projections.Property("Name")));
IList<string> names = c.List<string>();
I got this idea from this old StackOverflow question.
我从这个旧的 StackOverflow 问题中得到了这个想法。
回答by Jamie Ide
You typically don't. It rarely makes sense to have a partially populated business object.
你通常不会。拥有部分填充的业务对象几乎没有意义。
Why would you want to do this?
你为什么想做这个？
回答by Moskie
What about executing a query by string?
按字符串执行查询怎么样？
IList<string> names = session.CreateQuery("select name from Tribbles").List<string>();
回答by Shiva
You can do something like this :
你可以这样做：
IQuery query = dao.GetQuery(@"SELECT u.Id
FROM UserImpl u
WHERE u.UserName = :username");
query.SetParameter("username", username);
return (long)query.UniqueResult();
回答by Ulf ?kerstedt
Almost five years later..., this is what you could do using NHibernate.Linq:
差不多五年后......，这就是你可以使用 NHibernate.Linq 做的事情：
IList<string> names = session.Query<Tribble>().Select(t => t.Name).ToList()
