mysql - Modeling a directed graph with a special center node -

-

I am looking for opinions about a modeled model of a specific node.

Special node:

  1. It can not contain any edges.
  2. Can not Remove.

Current design:

Tables: Nodes, edges have two columns in the edges; The node refers to each record in the table.

Rather than storing the special node as the first record in the nodes table, I decided not to keep it completely recordable for its creation, from any database queries, in the table of edges, by tap In the context of node, by_node_id takes a special meaning in the column.

My motivation for using this design was that I would not be worried about defending the center node record by deletion / modification or being referenced in the to_node_id column of the edge table. It automatically prevents one edge from going to the same node I know that there are some drawbacks in this design, such as that is not able to make the _node_id and to_node_id the whole primary key, and possibly too much

I am currently leaning towards the center node and making a check for that node in relevant database methods. What is the best way to go about this design?

I see some arguments against using zero in this case.

  1. If the nodes contain actual data then you have hard-code data for the central node in the application.
  2. If the middle node can be changed, then the problem will be.
  3. The general meaning of zero is that there is no value or value is unknown. Because of this, it may be unwelcome to any other person who approaches the proposed design.

In other words, I would prefer to place a row in the database for the central node.


Comments

Post a Comment

Popular posts from this blog

c# - ListView onScroll event -

-
I am programming a simple C # application, and I need a Scallow event on the list view. So I inherited the original ListView class created in ListviewEx witch. I found out how to locate the scroll message from WinAPI and I modified the WndProc method. Now I have this WndProc: protected override zero WndProc (Ref message message) {base.WndProc (Ref I); If (m.msg == WM_VSCROLL) {onScroll (This, New EventArgs ()); }} But the problem is, I do not know how to know about scrolling information. This data should be in wParam, but there is a LOWORD macro ++ like in C in C # and I switch to find the criteria like SB_ below, SB_ENDSCROLL, SB_PAGEUP etc. there any way Need to change the LOWORD macro from C #? Or any other way to find the necessary parameters about scrolling? You can define the WParam constants as the following: Private const int WM_HSCROLL = 0x114; Private Constant WM_VSCROLL = 0x115; Private contact int SBHOZZ = 0; Private Consultant SB_VERT = 1; Private Con...
Read more

PHP - get image from byte array -

-
I am trying to create a back-end for my mobile application. I am sending the content of an image in the body of the HTTP request (output stream) as a byte array, I want to read this stream of bytes in PHP scripts and take back an image. Can anyone tell me how can I do this? Thank you. You can obtain the request body $ body = Reading from file_get_contents ('php: // input'); What you do with that data Depending on you, you can write the data in a file as you mentioned that this is image data, you can drop the data into the object can do. Another option is to use and load the image.
Read more

Linux Terminal Problem with Non-Canonical Terminal I/O app -

-
I have a small app written in C to run on Linux. Part of the app accepts user-input from keyboard , And it uses non-canonical terminal mode so that it can respond to each keystroke. The section of the code that accepts input is a simple task that is called repeatedly in the loop: char get_input () {char C = 0; Int res = reading (input_tamille, & amp; c, 1); If (RSS == 0) 0 returns; If (res == -1) {/ * snip error handling * /} return c; } It reads a letter from the terminal if there is no input within a given time limit, (c_cc [VTIME] value in the vocabulary structure), read () 0 And get_input () is called again It all works very well, I have recently discovered that if you run this app in a terminal window, and then the app Close the terminal window without ending, the app will not exit Received, but CPU intensive launches into an infinite loop, where the read () returns 0 without waiting continued. So how can I get out of the apple if it runs from the terminal win...
Read more