使用Entity Framework和LINQ从数据库查询动态类别/子类别

Question

I need to come up with a solution to have infinite category and subcategories in a database. So this is my idea: creating a table that references parents/child as follows:

As you can see items can be followed down by its id and ParentItemID . However I don't know how I can apply this solution using LINQ.

I have create a model for above table as follow:

    class Items
    {
        public int id { get; set; }
        public string ItemName { get; set; }
        public int ParentItemID { get; set; }
    }

I have loaded list of 'Items' form database using EF, and I would like to query the list so it can be grouped and browsed like this:

How can it be done?

Thank in advance for any help.

Answer 1

1) With your model Add a foreign key (self reference) between parent item id and item id.

CREATE TABLE [dbo].[26957446_All]([id] [int] NOT NULL,[name] [varchar](50) NOT NULL, [parentid] [int] NULL, CONSTRAINT [PK_26957446_All] PRIMARY KEY CLUSTERED ( [id] ASC )
ALTER TABLE [dbo].[26957446_All]  WITH CHECK ADD  CONSTRAINT [FK_26957446_Circular] FOREIGN KEY([parentid]) REFERENCES [dbo].[26957446_All] ([id])
ALTER TABLE [dbo].[26957446_All] CHECK CONSTRAINT [FK_26957446_Circular]

Generated model: , notice the self reference, names auto generated, All1 are children, All2 is parent reference.

  var ents = new DynamicCategory.StackOverflowEntities26957446All();
  // all root items loop
  foreach (var item in ents.C26957446_All.Where(x => x.C26957446_All2 == null))
  {
    Console.WriteLine("Id: {0} Name: {1}", item.id, item.name);
    PrintChildrenRecursively(item);
  }  

  static int i = 1; //level
  static void PrintChildrenRecursively (DynamicCategory.C26957446_All item)
  {
    foreach (var c in item.C26957446_All1)
    {
      Console.WriteLine("{2} Child Id: {0} Name: {1}", c.id, c.name, new string('\t', i));

    if (c.C26957446_All1.Count > 0)
    {
      i++;
      PrintChildrenRecursively(c);
      i--;
    }
    Console.WriteLine();
    }
  }

Output:

2) With a different db organization . Separate items and relationships into separate tables. Add foreign keys from Relationship.Child and Relationship.Parent to Items table.

CREATE TABLE [dbo].[26957446_Items]([id] [int] NOT NULL, [name] [varchar](50) NOT NULL, CONSTRAINT [PK_26957446_Items] PRIMARY KEY CLUSTERED ([id] ASC))
CREATE TABLE [dbo].[26957446_Relationships](ParentId] [int] NOT NULL, [ChildId] [int] NOT NULL, CONSTRAINT [PK_Relationships] PRIMARY KEY CLUSTERED ([ParentId] ASC, [ChildId] ASC ))
ALTER TABLE [dbo].[26957446_Relationships]  WITH CHECK ADD  CONSTRAINT [FK_Child] FOREIGN KEY([ChildId]) REFERENCES [dbo].[26957446_Items] ([id]) 
ALTER TABLE [dbo].[26957446_Relationships] CHECK CONSTRAINT [FK_Child] 
ALTER TABLE [dbo].[26957446_Relationships]  WITH CHECK ADD  CONSTRAINT [FK_Parent] FOREIGN KEY([ParentId]) REFERENCES [dbo].[26957446_Items] ([id]) 
ALTER TABLE [dbo].[26957446_Relationships] CHECK CONSTRAINT [FK_Parent]

Generated EF: , notice only class generated with both bottom-up and top-down references. Output is identical, code is very much similar with the exception: item.ItemChildren are children, and root items acces is :

var ents = new DynamicCategory.StackOverflowEntities26957446();
ents.C26957446_Items.Where (x=>x.ItemParents.Count==0)