Linq如何根据父项目的属性查询项目列表以获取子集合的组合列表

Question

Hi say I have the objects:

public class InvoiceLine
{
}

and

public class InvoiceHeader
{
    public char Group { get; set; }
    public List<InvoiceLine> InvoiceLines { get; set; }
}

Data is set up for them as follows:

var invoiceLine1 = new InvoiceLine();
var invoiceLine2 = new InvoiceLine();
var invoiceLine3 = new InvoiceLine();
var invoiceLine4 = new InvoiceLine();
var invoiceLine5 = new InvoiceLine();
var invoiceLine6 = new InvoiceLine();
var invoiceLine7 = new InvoiceLine();
var invoiceLine8 = new InvoiceLine();

var invoiceHeader1 = new InvoiceHeader { Group = 'A', InvoiceLines = new List<InvoiceLine> { invoiceLine1, invoiceLine2 } };
var invoiceHeader2 = new InvoiceHeader { Group = 'A', InvoiceLines = new List<InvoiceLine> { invoiceLine3, invoiceLine4 } };
var invoiceHeader3 = new InvoiceHeader { Group = 'B', InvoiceLines = new List<InvoiceLine> { invoiceLine5, invoiceLine6 } };
var invoiceHeader4 = new InvoiceHeader { Group = 'B', InvoiceLines = new List<InvoiceLine> { invoiceLine7, invoiceLine8 } };

var invoiceHeaders = new List<InvoiceHeader>
{
    invoiceHeader1,
    invoiceHeader2,
    invoiceHeader3,
    invoiceHeader4
};

What I want to get is a Lists of invoiceLines for each Group.

So I would like for group A:

invoice1 , invoice2 , invoice3 and invoice4

and for group B:

invoice5 , invoice6 , invoice7 and invoice8

The furthest I got was:

var invoiceLinesGroupA = invoiceHeaders.SelectMany(x => x.InvoiceLines);

which as far as I can tell will get all eight invoiceLines. Somehow I need to discrimate by group to just get the ones for groupA and do likewise for groupB.

Can anyone help with this?

Answer 1

You may just want to group the invoice headers by the group:

var groups = invoiceHeader.GroupBy(ih => ih.Group);

Then you can access the lines of the groups:

foreach(var group in groups)
{
    Console.WriteLine("Group " + group.Group);
    Console.WriteLine("Lines:");
    Console.WriteLine(string.Join(", ", group.SelectMany(h => h.InvoiceHeader.InvoiceLines)));
}

Output would be something like

Group A
Lines:
invoice1, invoice2, invoice3, invoice4

Group B
Lines:
invoice5, invoice6, invoice7, invoice8

Answer 2

var regrouped = invoiceHeaders
    .SelectMany(
        header => header.InvoiceLines,
        (header, line) => new { header, line }
    )
    .GroupBy(
        o => o.header.Group,
        o => o.line,
        (groupName, lines) => new InvoiceHeader
        {
            Group = groupName,
            InvoiceLines = lines.ToList()
        }
    )
    .ToList();

Answer 3

Look at this overload of Enumerable.SelectMany

var result = invoiceHeaders
               .SelectMany(x => x.InvoiceLines,
                           (group, InvoiceLine)=>{group, InvoiceLine})
               .Where(res => res.group='A');

Answer 4

This should do it:

        var test = from h in invoiceHeaders
                   from i in h.InvoiceLines
                   group i by h.Group
                   into g
                   select new {key = g.Key, rows = g.ToArray()};

You can then access the items like this test.Where(x => x.key == 'A').rows

Answer 5

var q = from current in myInvoiceHeaders
                join c in myInvoiceLines on current.Id equals c.Header.Id into linesByHeader                    
                select new {
                    Header = current,
                    Lines = linesByHeader
                };

should work under the premise that you have a criteria to join both entities.