my code:
DB::transaction(function () {
$foo = Foo::whereId(1)->lockForUpdate()->with('bars')->first();
// dump foo & bars
// update foo's columns
// update bars' columns
});
and I run this code at the same time twice, first time it can update correctly, but the second time when I query the foo, foo's columns is correct, but the bars are still old(in database it's correct), why is it and how to solve it?
Since you are using lockForUpdate() and want to use the new data after you update, you need to re-hydrate the model using refresh()
The refresh method will re-hydrate the existing model using fresh data from the database. In addition, all of its loaded relationships will be refreshed as well:
https://laravel.com/docs/9.x/eloquent#refreshing-models
There is a great answer by NoOorZ24 # Laravel lockforupdate (Pessimistic Locking) explaining how the lock for transaction works to further clarify.
Related
I am using below code to get records with specified condition, and then to update only the same records.
$this->db->where('Parameter1', 'TRUE');
$query = $this->db->get('Messages');
$this->db->where('Parameter1', 'TRUE');
$this->db->set('Parameter1', 'FALSE');
$this->db->update('Messages');
This works, but calling two times the same query using where() command seems like wasting of server power. Is it possible to make get() command not reset query or to use the previous record set in the update command?
I doubt this is something you really need to worry about taking up too many resources, and you can't really reuse the where clause in the actual sql query. But if you'd like you can refactor to get slightly cleaner code.
$unread = array('Parameter1'=>TRUE);
$read = array('Parameter1'=> FALSE);
$query = $this->db->get_where('Messages', $unread);
$this->db->update('Messages', $read, $unread);
Note:
In your code your getting every element where Parameter1 is set to true, and then changing every one of those elements to false. This almost certainly is not desirable, but perhaps it is a problem you take care of somewhere else in your real application.
I currently have a database setup within an html page and my requirement is to update a single row within the application.
I could refresh the database with "fresh" data, but that would require too much time.
I had a look at
dbSports().update("aName", object.aname);
However it seems to update all the records in my database instead of just one. Are there any answers to this particular issue?
The Documentation on the matter is missing a major chunk of information, but is covered in a presentation done by the author of the library (http://www.slideshare.net/typicaljoe/better-data-management-using-taffydb-1357773) [Slide 30]
The querying object needs to be pointing to the object you want to update and editing happening from there. i.e.
var obj = dbObject({
Id : value.id
}).update(function() {
this.aName = object.aname;
return this;
});
Where the object in the query points to the ID of the row and the update function then points to it aswell and the callback updates the value that the application needs to update
you first have to find the matching record, then update it
yourDB({"ID":recordID}).update({
"col1":val1,
"col2":val2,
"col3":val3
});
I have a view ObjectDisplay that is composed of two relevant tables: Object and State. State represents the state of an Object, and the view pulls some of the details from the most recent State for each Object.
On the page that is displaying this information, a user can enter some comments, which creates a new State. After creating the new State, I immediately pull the Object from ObjectDisplay and send it back to be dropped into a partial view and replace the Object in the grid on the page.
// Add new State.
db.States.Add(new State()
{
ObjectId = objectId,
Comments = comments,
UserName = username
});
// Save the changes (executes all of the above).
db.SaveChanges();
// Return the new Object information.
return db.Objects.Single(c => c.ObjectId == objectId);
According to my db trace, the Single call occurs about 70 ms after the SaveChanges call, and it occurs on the same SPID.
Now for the issue: The database defaults the value of RecordDate in State to GETUTCDATE() - I don't provide the date myself. What I'm seeing is that the Object returned has the State's RecordDate of the old State and the Comments of the new State information of the old State. I am seeing that the Object returned has the old State's information. When I refresh the page, all the correct information is there, but the wrong information is returned in the initial call from the database/EF.
So.. what could be wrong? Could the view not be updating quickly enough? Could something be going on with EF? I don't really know where to start looking.
If you've previously loaded the same Object entity in the same DbContext, EF will return the cached instance with the stale values, and ignore the values returned from SQL.
The simplest solution is to reload the entity before returning it:
var result = db.Objects.Single(c => c.ObjectId == objectId);
db.Entry(result).Reload();
return result;
This is indeed odd. In SQL Server views are not persisted by default and therefore show changes in the underlying data right away. You can create a clustered index on a view with effectively persists the query, but in that case the data is updated synchronously, so you should see the change right away.
If you are working with snapshot isolation level your changes might not be visible to other SPIDs right away, but as you are on the same SPID and do not use snapshot isolation, this cant be the culprit either.
The only thing left at this point is the application layer. Are you actually using the result of the Single call higher up in the call stack or does that get lost somewhere. I assume that a refresh of the page uses a different code path, which would explain why it is working there.
I am currently getting products from one site, storing them in a database, and then having their prices display on another site. I am trying to get the prices from the one site to update daily in my database so the new updated prices can be displayed onto my other site.
Right now I am getting the products using an item number but have to manually go in and update any prices that have changed.
I am guessing I am going to have to use some kind of cronjob but not sure how to do this. I have no experience with cronjobs and am a noob with php.
Any ideas?
Thanks!
I have done some reading on the foreach loop and have written some code. But my foreach loop is only running once for the first item number. The foreach loop runs then goes to the "api.php" page but then stops. It doesn't continually loop for each item number. How do I tell it to go through all of item numbers in my database?
Also if you see anything else wrong in my code please let me know.
Thanks
....
$itemnumber = array("".$result['item_number']."");
foreach ($itemnumber as $item_number) {
echo "<form method=\"post\" action=\"api.php\" name=\"ChangeSubmit\" id=\"ChangeSubmit\">";
echo "<input type=\"text\" name=\"item_number\" value=\"{$item_number}\" />";
echo "<script type=\"text/javascript\">
function myfunc () {
var frm = document.getElementById(\"ChangeSubmit\");
frm.submit();
}
window.onload = myfunc;
</script></form>";
}
}
If you already retrieve the product data from an external site and store it in a local database, updating the prices from the same source should be no problem to you. Just retrieve the data, iterate through it in a foreach loop or similar and update the prices to the database based on the item number.
Once you have created the update script and run it manually, adding it as a cronjob will be as simple as running the command `crontab -e´ and adding this row to execute your script every midnight:
0 0 * * * /usr/local/bin/php /path/to/your/script.php
Don't forget to use the correct path for PHP for your system, running which php in the shell will tell you the path.
If you have cronjob's on your server, it'll be very apparent- You make a PHP script that updates it, and throw it in a daily cronjob.
However, I do it this way:
Method 1: At the beginning of every page request, check the last "update" time (you choose how to store it). If it's been more than a day, do the update and set the "update" time to the current time.
This way, every time someone loads a page and it's been a day since the last update, it updates for them. However, this means it's slower for random users, once a day. If this isn't acceptable, there's a little change:
Method 2: If you need to update (via the above method of checking), start an asyncronous request for the data, handle the rest of the page, flush it to the user, then in a while loop wait until the request finishes and update it.
The downside to method 2 is that the user won't see the updated values, but, the benefit is that it won't be any more of a wait for them.
I have some tables in a MySQL database to represent records from a sensor. One of the features of the system I'm developing is to display this records from the database to the web user, so I used ADO.NET Entity Data Model to create an ORM, used Linq to SQL to get the data from the database, and stored them in a ViewModel I designed, so I can display it using MVCContrib Grid Helper:
public IQueryable<TrendSignalRecord> GetTrends()
{
var dataContext = new SmgerEntities();
var trendSignalRecords = from e in dataContext.TrendSignalRecords
select e;
return trendSignalRecords;
}
public IQueryable<TrendRecordViewModel> GetTrendsProjected()
{
var projectedTrendRecords = from t in GetTrends()
select new TrendRecordViewModel
{
TrendID = t.ID,
TrendName = t.TrendSignalSetting.Name,
GeneratingUnitID = t.TrendSignalSetting.TrendSetting.GeneratingUnit_ID,
//{...}
Unit = t.TrendSignalSetting.Unit
};
return projectedTrendRecords;
}
I call the GetTrendsProjectedMethod and then I use Linq to SQL to select only the records I want. It is working fine in my developing scenario, but when I test it in a real scenario, where the number of records is way greater (something around a million records), it stops working.
I put some debug messages to test it, and everything works fine, but when it reaches the return View() statement, it simply stops, throwing me a MySQLException: Timeout expired. That let me wondering if the data I sent to the page is retrieved by the page itself (it only search for the displayed items in the database when the page itself needs it, or something like that).
All of my other pages use the same set of tools: MVCContrib Grid Helper, ADO.NET, Linq to SQL, MySQL, and everything else works alright.
You absolutely should paginate your data set before executing your query if you have millions of records. This could be done using the .Skip and .Take extension methods. And those should be called before running any query against your database.
Trying to fetch millions of records from a database without pagination would very likely cause a timeout at best.
Well, assuming information in this blog is correct, .AsPagination method requires you to sort your data by a particular column. It's possible that trying to do an OrderBy on a table with millions of records in it is just a time consuming operation and times out.