2

我有一种方法可以使用 LINQ 对两个 DataTable 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，但我不知道如何解决它。

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。我已经尝试过将整个 LINQ 表达式转换为 IEnumerable 之类的显而易见的方法，但这会产生运行时异常。

任何想法将不胜感激！

编辑：

最后的方法：

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;
}
4

2 回答 2

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;
}
于 2013-08-29T15:24:27.070 回答
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;
于 2013-08-29T15:24:24.007 回答