I'm creating a CMS from scratch.
I'm looking for a way to set a value in my database following a specific condition.
The context here is I want to save records for the deleted or edited comments that would have been reported by the community.
Then I wanna view those logs/records but I have trouble defining wheter or not those values are deleted or edited.
( this is important to view the logs, obviously )
Here is the code i've done so far to insert the logs.
// Insert logs moderation
public function insertLogs($idCommentaire){
$sql ="INSERT INTO logs(com_id, com_date, com_author, com_content, post_id)
SELECT com_id, com_date, com_author, com_content, post_id FROM
comments WHERE com_id = ?";
$this->executeRequest($sql, array($idCommentaire));
}
Now I would like to set it up if it's modified or deleted, depending on which method I call this SQL, here is an example for the deletion :
$this->admin->insertLogs($idCommentaire);
$this->admin->suppressCom($idCommentaire);
I've created a new column ENUM from MySql ("deleted" "modified") but can't figure out how can I update this Logs table with the datas on it.
Here is the SQL I'm thinking about :
UPDATE logs SET type =("modified"OR"deleted") WHERE com_id = 70;
Note that it's not a good coding, just what I want to do in my mind.
I'm talking about plain MySQL here, if it's possible to combine it all in one request.
Otherwise I would set up 1 more request, 1 for each, but I don't know if it's really clean to do so.
What's your advices and thoughts about it ?
Thanks you all.
Your logic isn't too bad. However, I'll note a couple of things.
TYPE is a reserved word in MySQL and probably most RDBMSs. Pick
another name for your column that indicates if a post has been
modified or deleted.
There is at least one more state for a post; it's approved, or
published, or 'okay', or whatever you'd like to call it. So if you
create an ENUM field called
SomethingOtherThanTypeThatStillMeansType, or foo or
post_status or whatever, include fields for all potential states
your data may have, including deleted, modified, posted, not_yet_posted, edited, or whatever you think the system may support at the time of some future feature update.
You might consider using an INT type for your status field. I'm
thinking that might be a tad faster than an ENUM.
Related
Well, I'm afraid that I will not be able to post a minimum reproducible example, and for that I apologize. But, here goes nothing.
Ours is a weekly prepared meals service. I track order volume in many ways. Here is the structure of the relevant table:
So then I utilize the highlighted fields in many ways, such as indicating to delivery drivers if a customer is returning from the prior order being more than a month ago (last_order_w - prev_order_w > 4), for instance.
Lately I have been noticing that the data is not consistently updating properly. In the past 3 weeks, I would say it is an occurrence of 5%. If it were more consistent, I would be more confident in my ability to track down the issue, but I am not even sure how to provoke it, as I only really notice it after the fact.
The code that should cause the update is below:
<?php
//retrieve and iterate over IDs of orders placed since last synchronization.
$newOrders=array_map('reset',$dbh->query("select id from wp_posts where id > (select max(synced) from fitaf_weeks) and post_type='shop_order' and post_status='wc-processing'")->fetchAll(PDO::FETCH_NUM));
foreach($newOrders as $no){
//retrieve the metadata for the current order
$newMetas=array_map('reset',$dbh->query("select meta_key,meta_value from wp_postmeta where post_id=$no")->fetchAll(PDO::FETCH_GROUP|PDO::FETCH_UNIQUE));
//check if the current order is associated with an existing customer
$exist=$dbh->query("select * from fitaf_customers where id=".$newMetas['_customer_user'])->fetch();
//if not, gather the information we want to store from this post
$noExist=[$newMetas['_customer_user'],$newMetas['_shipping_first_name'],$newMetas['_shipping_last_name'],$newMetas['_shipping_address_1'],(strlen($newMetas['_shipping_address_2'])==0?NULL:$newMetas['_shipping_address_2']),$newMetas['_shipping_city'],$newMetas['_shipping_state'],$newMetas['_shipping_postcode'],$phone,$newMetas['_billing_email'],1,1,$no,$newMetas['_paid_date'],$week[3],$newMetas['_order_total']];
if($exist){
//if we found a record in the customer table, retrieve the data we want to modify
$oldO=$dbh->query("select last_order_id,last_order,last_order_w,lo,num_orders from fitaf_customers where id=".$newMetas['_customer_user'])->fetch(PDO::FETCH_GROUP|PDO::FETCH_ASSOC|PDO::FETCH_UNIQUE);
//make changes to the retrieved data, and make sure we are storing the most recently used delivery address and prepare the data points for the update command
$exists=[$phone,$newMetas['_shipping_first_name'],$newMetas['_shipping_last_name'],$newMetas['_shipping_postcode'],$newMetas['_shipping_address_1'],(strlen($newMetas['_shipping_address_2'])==0?NULL:$newMetas['_shipping_address_2']),$newMetas['_shipping_city'],$newMetas['_shipping_state'],$newMetas['_paid_date'],$no,$week[3],$oldO['last_order'],$oldO['last_order_id'],$oldO['last_order_w'],($oldO['num_orders']+1),($oldO['lo']+$newMetas['_order_total']),$newMetas['_customer_user']];
}
if(!$exist){
//if the customer did not exist, perform an insert
$dbh->prepare("insert into fitaf_customers(id,fname,lname,addr1,addr2,city,state,zip,phone,email,num_orders,num_weeks,last_order_id,last_order,last_order_w,lo) values(?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)")->execute($noExist);
}
else{
//if the customer did exist, update their data
$dbh->prepare("update fitaf_customers set phone=?,fname=?,lname=?,zip=?,addr1=?,addr2=?,city=?,`state`=?,last_order=?,last_order_id=?,last_order_w=?,prev_order=?,prev_order_id=?,prev_order_w=?,num_orders=?,lo=? where id=?")->execute($exists);
}
}
//finally retrieve the most recent post ID and update the field we check against when the syncornization script runs
$lastPlaced=$dbh->query('select max(id) from wp_posts where post_type="shop_order"')->fetch()[0];
$updateSync=$dbh-> query("update fitaf_weeks set synced=$lastPlaced order by id desc limit 1");
?>
Unfortunately I don't have any relevant error logs to show, however, as I documented the code for this post, I realized a potential shortcoming. I should be utilizing the data retrieved from the initial query of new posts, rather than a selecting the highest post id after performing this logic. However, I have timers running on my scripts, and this section hasn't taken over 3 seconds to run in a long time. So it seems unlikely, that the script, which runs on a cron every 5 minutes, is experiencing this unintended overlap?
While I have made the change to pop the highest ID off of $newOrders, and hope it solves the issue, I am still curious to see if anyone has any insights on what could cause this logic to fail at such a low occurrence.
It seems likely your problem comes from race conditions between multiple operations accessing your db.
First of all, your last few lines of code do SELECT MAX(ID) and then uses that value to update something. You Can't Do That™. If somebody else adds a row to that wp_posts table anytime after the entry you think is relevant, you'll use the wrong ID. I don't understand your app well enough to recommend a fix. But I do know this is a serious and notorious problem.
You have another possible race condition as well. Your logic is this:
SELECT something.
make a decision based on what you SELECTED.
INSERT or UPDATE based on that decision.
If some other operation, done by some other user of the db, intervenes between step 1 and step 3, your decision might be wrong.
You fix this with a db transaction. The ->beginTransaction() operation, well, begins the transaction. The ->commit() operation concludes it. And, the SELECT operation you use for step one should say SELECT ... FOR UPDATE.
I have a small PHP function on my website which basically does 3 things:
check if user is logged in
if yes, check if he has the right to do this action (DB Select)
if yes, do the related action (DB Insert/Update)
If I have several users connected at the same time on my website that try to access this specific function, is there any possibility of concurrency problem, like we can have in Java for example? I've seen some examples about semaphore or native PHP synchronization, but is it relevant for this case?
My PHP code is below:
if ( user is logged ) {
sql execution : "SELECT....."
if(sql select give no results){
sql execution : "INSERT....."
}else if(sql select give 1 result){
if(selected column from result is >= 1){
sql execution : "UPDATE....."
}
}else{
nothing here....
}
}else{
nothing important here...
}
Each user who accesses your website is running a dedicated PHP process. So, you do not need semaphores or anything like that. Taking care of the simultaneous access issues is your database's problem.
Not in PHP. But you might have users inserting or updating the same content.
You have to make shure this does not happen.
So if you have them update their user profile only the user can access. No collision will occur.
BUT if they are editing content like in a Content-Management System... they can overwrite each others edits. Then you have to implement some locking mechanism.
For example(there are a lot of ways...) if you write an update on the content keeping the current time and user.
Then the user has a lock on the content for maybe 10 min. You should show the (in this case) 10 min countdown in the frontend to the user. And a cancel button to unlock the content and ... you probably get the idea
If another person tries to load the content in those 10 min .. it gets an error. "user xy is already... lock expires at xx:xx"
Hope this helps.
In general, it is not safe to decide whether to INSERT or UPDATE based on a SELECT result, because a concurrent PHP process can INSERT the row after you executed your SELECT and saw no row in the table.
There are two solutions. Solution number one is to use REPLACE or INSERT ... ON DUPLICATE KEY UPDATE. These two query types are "atomic" from perspective of your script, and solve most cases. REPLACE tries to insert the row, but if it hits a duplicate key it replaces the conflicting existing row with the values you provide, INSERT ... ON DUPLICATE KEY UPDATE is a little bit more sophisticated, but is used in a similar situations. See the documentation here:
http://dev.mysql.com/doc/refman/5.0/en/insert-on-duplicate.html
http://dev.mysql.com/doc/refman/5.0/en/replace.html
For example, if you have a table product_descriptions, and want to insert a product with ID = 5 and a certain description, but if a product with ID 5 already exists, you want to update the description, then you can just execute the following query (assuming there's a UNIQUE or PRIMARY key on ID):
REPLACE INTO product_description (ID, description) VALUES(5, 'some description')
It will insert a new row with ID 5 if it does not exist yet, or will update the existing row with ID 5 if it already exists, which is probably exactly what you want.
If it is not, then approach number two is to use locking, like so:
query('LOCK TABLE users WRITE')
if (num_rows('SELECT * FROM users WHERE ...')) {
query('UPDATE users ...');
}
else {
query('INSERT INTO users ...');
}
query('UNLOCK TABLES')
Hello again Stackoverflow!
I'm currently working on custom forumsoftware and one of the things you like to see on a forum is a viewcounter.
All the approaches for a viewcounter that I found would just select the topic from the database, retrieve the number from a "views" column, add one and update it.
But here's my thought: If, lets say 400, people at the exact same time open a topic, the MySQL database probably won´t count all views because it takes time for the queries to complete, and so the last person (of the 400) might overwrites the first persons (of the 400) view.
Ofcourse one could argue that on a normal site this is never going to happen, but if you have ~7 people opening that topic at the exact same second and the server is struggleing at that moment, you could have the same problem.
Is there any other good approach to count views?
EDIT
Woah, could the one who voted down specify why?
I ment by "Retrieving the number of views and adding one" that I would use SELECT to retrieve the number, add one using PHP (note the tags) and updating it using UPDATE. I had no idea of the other methods specified below, that's why I asked.
If, lets say 400, people at the exact same time open a topic, the MySQL database apparently would count all the views because this is exactly what databases were invented for.
All the approaches for a viewcounter that you have found are wrong. To update a field you don't need to retrieve it, but just already update:
UPDATE forum SET views + 1 WHERE id = ?
So something like that will work:
UPDATE tbl SET cnt = cnt+1 WHERE ...
UPDATE is guaranteed to be atomic. That means no one will be able to alter cnt between the time it is read and the time it is replaced. If you have several concurrent UPDATE for the same row (InnoDB) or table (MyISAM) they have to wait their turn to update the date.
See Is incrementing a field in MySQL atomic?
and http://dev.mysql.com/doc/refman/5.1/en/ansi-diff-transactions.html
I've got a somewhat complicated question for you cakephp experts.
Basically, I have created a db table called "locations". Every month I will get this table sent to me in csv format from a client. Unfortunately, instead of updating this table, I will have to empty it and reimport all of the records. Unfortunately, I cannot alter this table at all.
Functionality wise, users will have the ability to look at a display of these records, and be able to choose to hide certain ones. This "hidden" attribute must be persistent and survive the month to month purging of all records.
I had all of this working yesterday. What I did was, create a separate table called location_properties (columns were: id(int), location_id(foreign key), is_hidden(boolean)). When showing these records, it would simply check to see if "is_hidden==true".
This was all well and good(AND WORKING!), but then my boss kind of gummed up the works. He told me to delete the "is_hidden" column from the table because it would be more efficient. That I should be able to simply check for the existence of the location_id to hide or show it.
It doesn't appear to be quite that simple. Anyone know how I can pull this off? I've tried everything I can think of.
Your boss is wrong.
It's more efficient to add your column, than it is too delete and re-import the locations every month.
Did he say it was less efficient, or did you do an actual benchmark to see if its harms performance too much?
At first glance I see 2 solutions:
1) add a condition array('Location.id' => 'NOT NULL')
2) change join type to right join
I hope this helps
I am just learning php as I go along, and I'm completely lost here. I've never really used join before, and I think I need to here, but I don't know. I'm not expecting anyone to do it for me but if you could just point me in the right direction it would be amazing, I've tried reading up on joins but there are like 20 different methods and I'm just lost.
Basically, I hand coded a forum, and it works fine but is not efficient.
I have board_posts (for posts) and board_forums (for forums, the categories as well as the sections).
The part I'm redoing is how I get the information for the last post for the index page. The way I set it up is that to avoid using joins, I have it store the info for latest post in the table for board_forums, so say there is a section called "Off Topic" there I would have a field for "forum_lastpost_username/userid/posttitle/posttime" which I woudl update when a user posts etc. But this is bad, I'm trying to grab it all dynamically and get rid of those fields.
Right now my query is just like:
`SELECT * FROM board_forums WHERE forum_parent='$forum_id''
And then I have the stuff where I grab the info for that forum (name, description, etc) and all the data for the last post is there:
$last_thread_title = $forumrow["forum_lastpost_title"];
$last_thread_time = $forumrow["forum_lastpost_time"];
$lastpost_username = $forumrow["forum_lastpost_username"];
$lastpost_threadid = $forumrow["forum_lastpost_threadid"];
But I need to get rid of that, and get it from board_posts. The way it's set up in board_posts is that if it's a thread, post_parentpost is NULL, if it's a reply, then that field has the id of the thread (first post of the topic). So, I need to grab the latest post_date, see which user posted that, THEN see if parentpost is NULL (if it's null then the last post is a new thread, so I can get all the info of the title and user there, but if it's not, then I need to get the info (title, id) of the first post in that thread (which can be found by seeing what post_parentpost is, looking up that ID and getting the title from it.
Does that make any sense? If so please help me out :(
Any help is greatly appreciated!!!!
Updating board___forums whenever a post or a reply is inserted is - regarding performance - not the worst idea. For displaying the index page you only have to select data from one table board_forums - this is definitely much faster than selecting a second table to get the "last posts' information", even when using a clever join.
You are better off just updating the stats on each action, New Post, Delete Post etc.
The other instances would not likely require any stats update (deletion of a thread would trigger a forum update, to show one less topic in the topic count).
Think about all the actions the user would do, in most cases, you dont need to update any stats, therefore, getting the counts on the fly is very inefficient and you are right to think so.
It looks like you've already done the right thing.
If you were to join, you'd do it like this:
SELECT * FROM board_forums
JOIN board_posts ON board_posts.forum_id = board_forums.id
WHERE forum_parent = '$forum_id'
The problem with that, is that it gets you every post, which is not useful (and very slow). What you would want to do is something like this
SELECT * FROM board_forums
JOIN board_posts ON board_posts.forum_id = board_forums.id ORDER BY board_posts.id desc LIMIT 1
WHERE forum_parent = '$forum_id'
except SQL doesn't work like that. You can't order or limit on a join (or do many other useful things like that), so you have to fetch every row and then scan them in code (which sucks).
In short, don't worry. Use joins for the actual case where you do want to load all forums and all posts in one hit.
The simple solution will result in numerous queries, some optional, as you're already discovered.
The classic approach to this is to cache the results, and only retrieve it once in a while. The cache doesn't have to live long; even two or three seconds on a busy site will make a significant difference.
De-normalizing the data into a table you're already reading anyway will help. This approach saves you figuring out optional queries and can be a bit of a cheap win because it's just one more update when an insert is already happening. But it shifts some data integrity to the application.
As an aside, you might be running into the recursive-query problem with your threads. Relational databases do not store heirarchical data all that well if you use a "simple" algorithim. A better way is something sometimes called 'set trees'. It's a bit hard to Google, unfortunately, so here are some links.