我有一个多选复选框。根据检查的是哪一个,我想将结果合并到一个查询中。有点像:
if (Checkbox1.Checked)
{
var query1 = from t in table1 ...
}
if (Checkbox2.Checked)
{
var query2 = from t in table2 ...
}
DataGridView1.DataSource = query1.Union(query2); // obviously doesnt
// work since query1 and query2 are not defined in this scope.
知道如何有选择地组合这些吗?
答案 0 :(得分:8)
假设查询类型相同,您可以在条件语句之外定义查询。
首先,一个辅助方法,它创建一个与参数类型相同的空枚举:
static IEnumerable<T> CreateEmptyEnumerable<T>(IEnumerable<T> templateQuery)
{
return Enumerable.Empty<T>();
}
然后,新代码:
var query1 = from t in table1 ...
var query2 = from t in table2 ...
var finalQuery = CreateEmptyEnumerable(query1);
if (Checkbox1.Checked)
{
finalQuery = query1;
}
if (Checkbox2.Checked)
{
finalQuery = finalQuery.Union(query2);
}
DataGridView1.DataSource = finalQuery.ToList(); // to avoid re-enumeration
这样做很好,因为查询在枚举之前不会被实际执行,就像调用ToList()
一样。
答案 1 :(得分:1)
使用Rx,您可以执行以下操作:
public partial class _Default : System.Web.UI.Page
{
IEnumerable<int> table1;
IEnumerable<int> table2;
protected void Page_Load(object sender, EventArgs e)
{
table1 = Enumerable.Range(0, 10);
table2 = Enumerable.Range(10, 10);
}
protected void Button1_Click(object sender, EventArgs e)
{
var query =
Observable.If(() => CheckBox1.Checked,
(from t in table1 select t).ToObservable(), Observable.Empty<int>())
.Concat(
Observable.If(() => CheckBox2.Checked,
(from t in table2 select t).ToObservable(), Observable.Empty<int>())
);
query.Subscribe(i => Response.Write(i));
}
}
答案 2 :(得分:0)
如果您不使用var但已知类型,则可以通过
初始化query1和query2 如果未选中复选框,则 Enumerable.Empty<T>
。
答案 3 :(得分:0)
我刚刚在一个控制台应用程序中试过这个,因为我很好奇,它只是起作用....
class Program
{
private class Data1
{
public int Code1 { get; set; }
public string Value1 { get; set; }
}
private class Data2
{
public int Code2 { get; set; }
public string Value2 { get; set; }
}
static void Main(string[] args)
{
var data1 = new[] { new Data1 { Code1 = 1, Value1 = "one" }, new Data1 { Code1 = 2, Value1 = "two" }, new Data1 { Code1 = 3, Value1 = "three" } };
var data2 = new[] { new Data2 { Code2 = 101, Value2 = "aaa" }, new Data2 { Code2 = 102, Value2 = "bbb" }, new Data2 { Code2 = 103, Value2 = "ccc" } };
var query1 = from d1 in data1 select new { code = d1.Code1, text = d1.Value1 };
var query2 = from d2 in data2 select new { code = d2.Code2, text = d2.Value2 };
var datasource = query1.Union(query2);
foreach (var d in datasource)
{
Console.WriteLine(d);
}
}
}
但是,如果我将匿名类型中的字段名更改为不同,则会出现编译器错误,因此看起来关键是要在匿名类型中使用相同的名称。或者只是将结果定义为:)