创建树：递归或表达式树C＃

Question

I have three DataSets. DataSet 1 has all the parent Ids, DataSet 2 has children of DataSet 1 and DataSet 3 has children of DataSet3.

I want to build a DataSet of tree like structures with Id of DataSet1 as root node.

DataSet 1-

<NewDataSet>
    <Table>
        <Id>A</Id>
        <Desc>ABC</Desc>
    </Table>
    <Table>
        <Id>B</Id>
        <Desc>DEF</Desc>
    </Table>
    <Table>
        <Id>C</Id>
        <Desc>PQR</Desc>
    </Table>
</NewDataSet>

DataSet 2-

<NewDataSet>
    <Table>
        <ParentId>A</ParentId>
        <Id>AA</Id>
        <Desc>ABC</Desc>
    </Table>
    <Table>
        <ParentId>B</ParentId>
        <Id>BB</Id>
        <Desc>DEF</Desc>
    </Table>
    <Table>
        <ParentId>B</ParentId>
        <Id>CB</Id>
        <Desc>PQR</Desc>
    </Table>
</NewDataSet>

DataSet 3-

<NewDataSet>
    <Table>
        <ParentId>AA</ParentId>
        <Id>AAA</Id>
        <Desc>ABC</Desc>
    </Table>
    <Table>
        <ParentId>BB</ParentId>
        <Id>BBB</Id>
        <Desc>DEF</Desc>
    </Table>
    <Table>
        <ParentId>BB</ParentId>
        <Id>CBB</Id>
        <Desc>PQR</Desc>
    </Table>
</NewDataSet>

Result Should be like this if don't specify any root node or if I want the children nodes or not:

GetTree(null, false);

<NewDataSet>
    <Table>
        <Id>A</Id>
        <Desc>ABC</Desc>
        <HasChildren>True</HasChildren>
        <NewDataSet>
            <Table>
                <Id>AA</Id>
                <Desc>ABC</Desc>
                <HasChildren>True</HasChildren>
                <DataSet>
                    <Table>
                        <Id>AAA</Id>
                        <Desc>ABC</Desc>
                        <HasChildren>False</HasChildren>
                    </Table>    
                </DataSet>
            </Table>
        </NewDataSet>
    </Table>
    <Table>
    ..... //All Root Nodes and their children
    </Table>
</NewDataSet>

But If I Provide an Id and also provide if I want the Id's children. GetTree("BB", true);

<NewDataSet>
    <table>
        <Id>BB</Id>
        <Desc>ABC</Desc>
        <HasChildren>True</HasChildren>
        <DataSet>
            <Table>
                <Id>BBB</Id>
                <Desc>ABC</Desc>
                <HasChildren>False</HasChildren>
            </Table>
            <Table>
                <Id>CBB</Id>
                <Desc>PQR</Desc>
                <HasChildren>False</HasChildren>
            </Table>
        </DataSet>
    </table>
</NewDataSet>

GetTree("BB", false);

<NewDataSet>
    <table>
        <Id>BB</Id>
        <Desc>ABC</Desc>
        <HasChildren>True</HasChildren>
    </table>
</NewDataSet>

I know I can do this with Nested Foreach but I want to write a recursive function to perform this operation. I have been searching the Internet for 2 days now for some examples and not able to do this. Any reference to a website would also help me alot.

Answer 1

Foreach is probably still the way to go, but instead of nested, you would just use it once for each 'node'.

public class MyDataSet
{
    public string ID {get;set;}
    public string Description {get;set;}
    public readonly List<MyDataSet> Children = new List<MyDataSet>();
    public bool HasChildren 
    {
        get { return Children.Count > 0 }
    }
    public void GetTree(string id, bool includeChildren)
    {
        MyDataSet mySet = id == null ? this : Children.FirstOrDefault(child => child.ID == id);

        if(mySet == null) return;
        // TODO: handle mySet

        if(includeChildren)
        {
            foreach (MyDataSet child in Children)
            {
                child.GetTree(null, true);
            }
        }
    }
}