如何从 SqlLite 数据库加载 TreeView 节点

Question

I am trying to load nodes into ac# winform treeview using System.Data.SQLite.

Currently my database table looks like this:

ID  Parent_ID  Name 
1   0          Apple
2   0          Pear 
3   2          Grapes 
4   3          Banana

I need my treeview to look like this:

Apple
Pear
-> Grapes
-> -> Banana

'Grapes' has a Parent_ID of '2', making it a child node of 'Pear', and 'Banana' has a Parent_ID of '3', making it a child node of 'Grapes'.

I'm not very experienced with SQL and am not sure how to go about getting the data out of my SQLite file 'Database.db', containing a table 'MyTable'.

Any help is much appreciated.

Answer 1

Try following :

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication41
{
    public partial class Form1 : Form
    {
        DataTable dt = null;
        public Form1()
        {
            InitializeComponent();

            dt = new DataTable();
            dt.Columns.Add("ID", typeof(int));
            dt.Columns.Add("Parent_ID", typeof(int));
            dt.Columns.Add("Name", typeof(string));

            dt.Rows.Add(new object[] {1, 0, "Apple"});
            dt.Rows.Add(new object[] {2, 0, "Pear"});
            dt.Rows.Add(new object[] {3, 2, "Grapes"});
            dt.Rows.Add(new object[] {4, 3, "Banana"});

            TreeNode node = new TreeNode("Root");
            treeView1.Nodes.Add(node);
            int parentID = 0;
            MakeTree(parentID, node);

            treeView1.ExpandAll();
        }

        public void MakeTree(int parentID, TreeNode parentNode)
        {
            foreach(DataRow row in dt.AsEnumerable().Where(x => x.Field<int>("Parent_ID") == parentID))
            {
                string name = row.Field<string>("Name");
                int id = row.Field<int>("ID");
                TreeNode node = new TreeNode(name);
                parentNode.Nodes.Add(node);
                MakeTree(id, node);

            }
        }
    }
}

Answer 2

Many thanks to Jdweng for providing a solution.

I modified their code slightly so that it didn't rely on making the datatable manually and instead took it from my SQLite database file.

Jdweng's code also made a 'Root' node which was not necessary for my application so I changed it to only include the nodes included in my SQLite DB table.

I also needed to change the 'MakeTree' method to look for Int64 as I was receiving an error, 'Specified cast is not valid' when querying ID and Parent_ID.

using System;
using System.Data;
using System.Data.SQLite;
using System.Linq;
using System.Windows.Forms;

namespace TreeView_SQL_Loader
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            DataTable DT = new DataTable();

            SQLiteConnection sql_con = new SQLiteConnection("data source=\"mydatabase.db\"");
            sql_con.Open();
            SQLiteCommand sql_cmd = sql_con.CreateCommand();
            sql_cmd.CommandText = "SELECT * FROM mytable";
            SQLiteDataAdapter DA = new SQLiteDataAdapter(sql_cmd.CommandText, sql_con);

            DA.Fill(DT);

            sql_con.Close();


            int parentID = 0;
            MakeTree(parentID, treeView1.Nodes, DT);

            treeView1.ExpandAll();
        }

        public void MakeTree(Int64 parentID, TreeNodeCollection parentNode, DataTable DT)
        {
            foreach (DataRow row in DT.AsEnumerable().Where(x => x.Field<Int64>("Field2") == parentID))
            {
                string name = row.Field<string>("Field3");
                Int64 id = row.Field<Int64>("Field1");
                TreeNode node = new TreeNode(name);
                parentNode.Add(node);
                MakeTree(id, node.Nodes, DT);

            }
        }
    }
}