使用JavaScript从数据库检索深层数据结构

Question

I have a data structure like below:

Task(id,name,subTasks[Task])

But the problem is the subTasks can contain Tasks which have another subTasks. This can run to very deep like this:

Task1 Contains SubTask1

SubTask1 contains it's sub tasks

and you can understand this can be run to very deep.

I can retrieve these data from a database tables. But how can I store this in a data structure in java script. Using for loops without knowing the deep is useless and not a elegant way. What would be the best data structure and data traversal way?

Answer 1

If you want to transfer arbitrarily-nested data structures to and from some other program (perhaps written in some other language), JSON format is a good format, which can be easily read or written in JavaScript -- see JSON objects in JavaScript . But there is no need for JSON if you're going to create and use such structures entirely internally in a single JavaScript program.

The general technique to traverse arbitrarily nested data structures is recursion . (Some people claim that "recursion" is one of the 2 most important things to learn about programming, even though they are not needed in 90% of written code -- Spolsky , Tim Bray , Jeff Atwood , Wenham , Sooriamurthi , etc. )

There are many stackoverflow questions that discuss recursion in JavaScript . You will get much better answers if you read a few of them, write a little bit of code, test it, and then post a short bit of code -- it doesn't have to be perfect.

// define the "Task" class
function Task(id, name, depth){
    this.id = id;
    this.name = name;
    this.depth = depth;
    this.subTask = []; // Use "[]" rather than "{}" so it works with "forEach".
    this.stringify_name_and_all_subtasks = function(depth){
        var return_string = this.depth + ":" + this.name + " ";
        // If "forEach" doesn't work for you,
        // use the "Compatibility" code in
        // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach
        this.subTask.forEach( function(entry){
            return_string += entry.stringify_name_and_all_subtasks(depth);
        });
        return return_string;
    };
};

Answer 2

All too often, programmers try to force the data to fit into a strict hierarchy, with nested data structures. ( DOM manipulation and Javascript Data Structures: Flat or Structured? , Hierarchy Considered Harmful , etc. )

However, non-nested structures are better when you don't have a pure hierarchy. Sometimes they work better even when you do have a pure hierarchy -- such as when you want to look up things without traversing the entire structure. For example, "What tasks depend on the sub-task named 'rotate stock' ?"

Perhaps one of the many alternatives to hierarchy might work better in your case. For example, an associative array:

<script>
"use strict";
// global task list
var tasklist_by_id = [];
var task_name_to_id = {};

// add a new task to global tasklist
function add_task(id, name, supertaskid){
    tasklist_by_id[ id ] = {"id":id, "name":name, "supertaskid":supertaskid};
    /* in other words,
    var new_task = {};
    new_task.id = id;
    new_task.name = name;
    new_task.supertaskid = supertaskid;
    tasklist_by_id[ id ] = new_task;
    */
    task_name_to_id[ name ] = id;
};

function ancestors_of( task_id ){
    if( task_id ){
        var my_name =  tasklist_by_id[ task_id ].name;
        var my_supertaskid = tasklist_by_id[task_id].supertaskid;
        var my_ancestors = ancestors_of( my_supertaskid );
        var ancestor_string = " -- " + my_name + my_ancestors;
        return ancestor_string;
    }else{
        return ".";
    };
};

function test(){
    add_task( 1, "Main task #1", 0 );
    add_task( 2, "Subtask 1", task_name_to_id[ "Main task #1" ] );
    add_task( 3, "Sub-subtask 1", task_name_to_id[ "Subtask 1" ] );
    add_task( 4, "Another Subtask of Main task 1", task_name_to_id[ "Main task #1" ] );
add_task( 5, "Sub-sub-subtask 1", task_name_to_id[ "Sub-subtask 1" ] );
    add_task( 6, "rotate_stock", task_name_to_id["Sub-sub-subtask 1" ])

    // What task is the parent task(s) of "rotate_stock" ?

    var some_task_name = "rotate_stock";
    var some_task_id = task_name_to_id[some_task_name];
    var ancestors = ancestors_of( some_task_id );

    alert("The ancestry line of " + some_task_name + " is " + ancestors);
}

test();
</script>