Enumerable.Concat无法正常工作 [英] Enumerable.Concat not working

问题描述

下面是代码:

string[] values = Acode.Split(',');
IEnumerable<Test> tst = null;

foreach (string a in values)
{
    if (tst== null)
        tst = entities.Test.Where(t=> (t.TCode == Convert.ToInt16(a)));
    else
        tst.Concat(entities.Test.Where(g => (g.TCode == Convert.ToInt16(a))));

}

return tst.ToList();

我无法在tst中获取所有记录，它只为数组中的最后一个值提供记录.

I am not able to get all the records in tst, it is giving me records only for the last value in array.

因此，如果我的数组包含1,2,3,4，则仅获取4的记录.而我需要将1,2,3和4的所有结果附加到tst中.

So if my array contains 1,2,3,4 I am getting records only for the 4. Whereas i need all the result for 1,2,3 and 4 get appended in tst.

任何帮助将不胜感激.

推荐答案

Concat不做任何修改-它返回一个新的序列，您当前正在忽略它.

Concat doesn't modify anything - it returns a new sequence, which you're currently ignoring.

但是，您应该只使用SelectMany来展平序列，而不是使用Concat:

However, rather than using Concat, you should just use SelectMany to flatten the sequence:

string[] values = Acode.Split(',');
return values.SelectMany(a => entities.Test.Where(t => t.TCode == Convert.ToInt16(a)))
             .ToList();

或更有效的方法是将values转换为List<short>，然后可以执行一个查询:

Or more efficiently, convert values into a List<short> and then you can do one query:

List<short> values = Acode.Split(',').Select(x => short.Parse(x)).ToList();
return entities.Test.Where(t => values.Contains(t.TCode)).ToList();

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