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POSorting IList<Person> by parent object which can be null
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copied!<p>I've been looking through the search system and not come across an answer for my problem, while these questions are similar and I even used some of them to make a start I've hit a brick wall.</p> <p>I've already checked out these questions</p> <ul> <li><a href="https://stackoverflow.com/questions/867164/algorithm-for-sorting-a-list-of-objects-in-c-sharp">Algorithm for sorting a list of objects in c#</a></li> <li><a href="https://stackoverflow.com/questions/15486/sorting-an-ilist-in-c-sharp">Sorting an IList in C#</a></li> </ul> <p>I have an object brought back by nHibernate called Person as follows</p> <pre><code> public class Person : IPerson, IComparable<Person>{ // private properties private int _id; private string _name; private Person _parent; private IList<Person> _children; private IList<Group> _groups; // public properties public virtual int id { get { return _id; } set { _id = value; } } public virtual string name { get { return _name; } set { _name= value; } } public virtual Person Parent { get { return _parent; } set { _parent = value; } } public virtual IList<Person> Children { get { return _children; } set { _children = value; } } public virtual IList<Group> Groups { get { return _groups; } set { _groups = value; } } // constructor public Person() {} // this section I added after looking on SO public virtual Int32 parentid { get { if (_parent == null) { return _id; } else { return _parent.id; } } } public virtual Int32 CompareTo(Person obj) { if (this.id == obj.id) return 0; return this.parentid.CompareTo(obj.parentid); } } </code></pre> <p>Then a method in my Dao which brings back a list of all the Person Objects in the database under a group. Unfortunately it brings them back in the order they were entered and I want to sort them into a parent child relationship.</p> <pre><code> i.e. (id,name,parent) person 1 (1,"Alice",null) person 2 (2,"Bob",1) person 3 (3,"Charlie",null) person 4 (4,"Dejgo",2) // child of a child person 5 (5,"Edgar", null) person 6 (6,"Florence", 3) </code></pre> <p>When I do a sort as mentioned in this <a href="https://stackoverflow.com/a/867250/728841">answer</a> like so:</p> <pre><code> class PeopleBLL : IPeopleBLL { // spring properties private IGroupsBLL _groupsBLL; private IPeopleDao _peopleDao; // public properties where spring sets up the links to the other dao and bll methods public IGroupsBLL { set{_groupsBLL = value;} } public IPeopleDao { set{_peopleDao= value;} } // constructor public PeopleBLL() { } // method we are interested in public IList<Person> GetAllInGroup(int groupID){ //get the group object Group groupObject = _groupsBLL.Get(groupID); // get the people in the group IList<Person> people = _peopleDao.GetAllInGroup(groupObject); // do something here to sort the people people.Sort(); // return the list of people to aspx page return people; } } </code></pre> <p>I get the list in the format</p> <pre><code> person 2 person 1 person 6 person 3 person 5 person 4 </code></pre> <p>but I want it in the format</p> <pre><code> person 1 person 2 person 4 person 3 person 6 person 5 </code></pre> <p>Any ideas?</p> <p><strong>EDIT:</strong> </p> <p>I didn't put the rest of this in because I didn't want to confuse the question by all the extra technologies used but since I was asked. Spring.Net is used to link up all the objects, I have a 3-tier architecture Front end (asp.net pages), Business layer, and Dao layer which communicates with the database. I have updated the GetAllInGroup() to show everything it does but it is only the sorting I am interested in. The Dao uses an nHibernate Criteria Query to get all the objects under the group as follows.</p> <pre><code> public IList<Person> getRegistrationsForDonor(Group groupObject) { IList<Person> rv = CurrentSession.CreateCriteria(typeof(Person),"p") .CreateCriteria("Groups","g") .Add(Expression.Eq("g.id", groupObject.id)) .List<Person>(); return rv; } </code></pre> <p>And all this is started in an aspx page in an object datasource</p> <pre><code> <asp:ObjectDataSource ID="ObjectDataSource1" OnObjectCreating="DataSource_ObjectCreating" runat="server" DataObjectTypeName="Domain.Person" TypeName="BusinessLayer.PersonBLL" DeleteMethod="delete" SelectMethod="GetAllInGroup" UpdateMethod="update"> <SelectParameters> <asp:ControlParameter ControlID="groupid" Type="Int32" DefaultValue="0" Name="groupID" /> </SelectParameters> </asp:ObjectDataSource> </code></pre> <p>which is then used by a gridview, so unfortunately I need to return a sorted IList from the BLL to the front end in the BLL method as a single IList.</p> <p><strong>Edit 2</strong> </p> <p>Sorry An assumption has been made that all parents will be null at the top level and I can understand where that assumption can come from but you could in theory have only children in the group so none of the object would have a parent of null. for example the following is a valid group.</p> <pre><code> person 2 (2,"Bob",1) person 4 (4,"Dejgo",2) // child of a child person 6 (6,"Florence", 3) </code></pre> <p>which I would hope would return </p> <pre><code> person 2 person 4 person 6 </code></pre> <p><strong>Edit 3</strong></p> <p>Unfortunately all of this could not be surmised in a comment so I will have to respond here.</p> <p>Having tried @jon-senchyna answer at 17:30, I am definitely getting closer, I have just tried this on some live data and it is nearly there but I seem to be running into problems with the children coming before the parents in the group. Take the following example in Group 1 there are 48 people, I will highlight the ones of interest.</p> <pre><code> (789, "person 1", null) (822, "Person 34", null) (825, "Person 37", 789) (3060, "Person 47", 822) (3061, "Person 48", 825) </code></pre> <p>This is the order they are returned from the database, but when they are put through the sort they are in the order</p> <pre><code> Person 48 - id: 3061 Person 37 - id: 825 Person 1 - id: 789 Person 47 - id: 3060 Person 34 - id: 822 </code></pre> <p>So the children are next to the parents but in the reverse order, where I would like them in the order </p> <pre><code> Person 1 - id: 789 Person 37 - id: 825 Person 48 - id: 3061 Person 34 - id: 822 Person 47 - id: 3060 </code></pre>

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