如何使用父子关系初始化列表

Question

Let's say I have the following classes:

public class Parent
{
   public string name;
   IList<Child> children;
}

public class Child
{
  public string parentName;
  public int age;
}

As it is understandable, each parent can have multiple children, and we can have multiple parents. What is the best way to initialize these classes? Is it better to get all of the parents, and all of the children from database then use LINQ?

IList<Parent> parents = GetParents() //assume this gets parents from db
IList<Child> children = GetChildren() //assume this gets children from db
foreach(Parent parent in parents)
{
   parent.children = children.Where(x=>x.parentName == parent.name).ToList();
}

or get all of the parents and iterate through each parent to query database by parentName to get children information? Due to requirement that I have, I cannot use datatable or dataset; I can only use datareader.

IList<Parent> parents = GetParents()//assume this gets parents from db
foreach(Parent parent in parents)
{
  parent.children = GetChildrenByParentName();//assume this gets parents from db by parentName
}

Thank you

Answer 1

If you are not able to leverage LinqToSql, Entity Framework or some other custom querying method and you must load all the parents and their children in the database per the manor you suggest then your first option is most likely superior. Assuming you'll query all the rows of both tables, the first option will result in only two database queries. In the second option you'll have as many queries as there are children plus the query for the parents.

EDIT

Additionally, especially if the data sets are large you can achieve further performance by using Enumerable.ToLookup . This essentially creates a sorted dictionary for you which makes searching for the appropriate children much more efficient as the framework can make use of a binary search. You could use it as follows:

var children = GetChildren().ToLookup(p => p.parentName);

... and then in your loop ...

parent.children = children[parent.name].ToList();

Answer 2

我认为，如果父级和子级具有基本字段，则数据库中应该为它们提供一个表，并具有一个附加属性Parent ，它引用同一表row，（因此它指向数据库中的父级），您可以确定，如果该行是子级或父级，如果其Parent不为null，则它应该是具有Parent的行的子元素