在Datset上的运行时使用C#动态Linq查询 [英] c# dynamic linq query at runtime on datset

问题描述

我需要您的帮助来解决一个小问题.我想使以下LINQ查询动态(在运行时)，因为我不知道数据库中将有多少个表(在运行时知道表名).

I need your help for a small problem. I would like to make the following LINQ query dynamic (at runtime) because I don´t know how many tables there will be in the database (the tablenames are known while runtime).

var query = from row1 in ds.Tables["tab1"].AsEnumerable()
        from row2 in ds.Tables["tab2"].AsEnumerable()
        from row3 in ds.Tables["tab3"].AsEnumerable()
        select new { row1, row2, row3 };

在这种情况下，是否可以在生成动态LINQ查询并将结果写入数据表或数组中?

Is this possible at generate a dynamic LINQ query in this case and write the result to a datatable or array?

提前谢谢！

推荐答案

此扩展方法可以创建以下项的笛卡尔积DataSet中的所有表行.

This extension method can create a cartesian product of all tables rows in a DataSet.

public static class Extensions
{
    public static IEnumerable<IEnumerable<T>> CartesianProduct<T>(this IEnumerable<IEnumerable<T>> sequences)
    {
        IEnumerable<IEnumerable<T>> emptyProduct = new[] { Enumerable.Empty<T>() };
        return sequences.Aggregate(
            emptyProduct,
            (accumulator, sequence) =>
                from accseq in accumulator
                from item in sequence
                select accseq.Concat(new[] { item })
            );
    } 
}

现在您可以通过以下方式使用它:

Now you can use it in this way:

IEnumerable<IEnumerable<DataRow>> allTablesRows = ds.Tables.Cast<DataTable>()
    .Select(table => table.AsEnumerable())
    .CartesianProduct();

输出:

foreach (var x in allTablesRows)
{
    foreach (DataRow row in x)
    {
        Console.WriteLine("table:{0} fields:{1}", 
            row.Table.TableName, 
            string.Join(",", row.ItemArray));
    }
}

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