我有一个方法,使用LINQ在两个DataTable上执行不匹配的查询。它产生了一个错误,通过在线查看,我已经确定了我认为错误发生的位置,但我无法弄清楚如何修复错误。
public IEnumerable<int> UnbilledAuditKeys(DataTable audits, string keyFieldName) {
var billedAudits =
from x in this.GetBilledAudits().AsEnumerable()
select new {
k = x.Field<int>(keyFieldName)
};
var allAudits =
from x in audits.AsEnumerable()
select new {
k = x.Field<int>(keyFieldName)
};
var unbilled =
from a in allAudits
join b in billedAudits on a.k equals b.k
into combined
from c in combined.DefaultIfEmpty()
where c == null
select new { // This is what's causing the error (I think)
k = a.k
};
return unbilled; // This line the compiler is rejecting
}
返回的错误是
Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<AnonymousType#1>' to 'System.Collections.Generic.IEnumerable<int>'. An explicit conversion exists (are you missing a cast?)
我不知道如何解决它。我已尝试将整个LINQ表达式转换为IEnumerable,但这会产生运行时异常。
任何想法都将不胜感激!
编辑:
最终方法:
public IEnumerable<int> UnbilledAuditKeys(DataTable rosliAudits, string keyFieldName) {
var billed = this.GetBilledAudits().AsEnumerable().Select(x => x.Field<int>(keyFieldName));
var allaudits = rosliAudits.AsEnumerable().Select(x => x.Field<int>(keyFieldName));
var unbilled = allaudits.Except(billed);
return unbilled;
}
答案 0 :(得分:3)
简单修复:
var unbilled =
from a in allAudits
join b in billedAudits on a.k equals b.k
into combined
from c in combined.DefaultIfEmpty()
where c == null
select a.k;
此外,其他两个查询似乎不需要匿名结构,最后一个可以大大简化:
public IEnumerable<int> UnbilledAuditKeys(DataTable audits, string keyFieldName) {
var billedAudits =
from x in this.GetBilledAudits().AsEnumerable()
select x.Field<int>(keyFieldName);
var allAudits =
from x in audits.AsEnumerable()
select x.Field<int>(keyFieldName);
var unbilled = allAudits.Except(billedAudits); // LINQ has many useful methods like this
return unbilled;
}
答案 1 :(得分:2)
直接选择您的字段,而不是创建新的匿名类型:
var unbilled =
from a in allAudits
join b in billedAudits on a.k equals b.k
into combined
from c in combined.DefaultIfEmpty()
where c == null
select a.k;