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Quote: read up on sql injection attacks as you are inviting someone to destroy your database.
What that means is this: never concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Always use Parameterized queries instead.
When you concatenate strings, you cause problems because SQL receives commands like:
SELECT * FROM MyTable WHERE StreetAddress = 'Baker's Wood' The quote the user added terminates the string as far as SQL is concerned and you get problems. But it could be worse. If I come along and type this instead: "x';DROP TABLE MyTable;--" Then SQL receives a very different command:
SELECT * FROM MyTable WHERE StreetAddress = 'x';DROP TABLE MyTable; Which SQL sees as three separate commands:
SELECT * FROM MyTable WHERE StreetAddress = 'x'; A perfectly valid SELECT
DROP TABLE MyTable; A perfectly valid "delete the table" command
And everything else is a comment.
So it does: selects any matching rows, deletes the table from the DB, and ignores anything else.
So ALWAYS use parameterized queries! Or be prepared to restore your DB from backup frequently. You do take backups regularly, don't you?
Sent from my Amstrad PC 1640
Never throw anything away, Griff
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!
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i doont no how to run the debugger
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Then learn!
The debugger is the biggest, badest, best tool in your box: chances are you will spend more time using that than you will your editor - even when you get more experience - because as you advance, so your code becomes more complex, and testing and diagnosing problems also becomes more complicated.
So find out how to use the debugger, and start finding your problems. Judging by the amount of HTML there is stuffed into your sample, you are using VS Code, so start reading here: Debugging in Visual Studio Code[^]
If you aren't, then start here: Navigate code with the debugger - Visual Studio | Microsoft Docs[^]
Sent from my Amstrad PC 1640
Never throw anything away, Griff
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!
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Ok so you do not know the basics of software development, you should get a beginners book and work through the examples as you read the book BEFORE you start trying to build.
Never underestimate the power of human stupidity -
RAH
I'm old. I know stuff - JSOP
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I am developing C# application compatible with ZKTeco finger device
therefore, when I can connect to device then when I enroll new employee to finger
device it shows bidirectional error.
please if someone knows that
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You should talk to the people who created it - they should provide technical support and will know more about their product than we will. If they don't, then find another supplier and demand your money back!
Sent from my Amstrad PC 1640
Never throw anything away, Griff
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!
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inho, another case (see my post) that illustrates why a requirement the OP search CP for resources prior to posting would be valuable. And, yes, I know that would be "iffy" to implement.
«Where is the Life we have lost in living? Where is the wisdom we have lost in knowledge? Where is the knowledge we have lost in information?» T. S. Elliot
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CodeProject is your friend: "C# ZKTeco Biometric Device Getting Started" by Ozesh Thapa, 2019: [^]
«Where is the Life we have lost in living? Where is the wisdom we have lost in knowledge? Where is the knowledge we have lost in information?» T. S. Elliot
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I am joining two list<t> type and each list has more than 800000 records.
may be this huge records causing this issue. my pc is 64 bit and 8GB RAM. i have windows 7 OS installed.
var QCViewAllHistValue1 = (from frmlst in cfList
join viewalllst in QCViewAllBrokerList1
on new
{
val = String.IsNullOrEmpty(frmlst.Section) ? "" : frmlst.Section.Trim().ToUpper(),
val1 = String.IsNullOrEmpty(frmlst.xFundCode) ? "" : frmlst.xFundCode.Trim().ToUpper(),
val2 = String.IsNullOrEmpty(frmlst.Period) ? "" : frmlst.Period.Replace("A", "").Replace("E", "").Trim().ToUpper(),
val3 = String.IsNullOrEmpty(frmlst.Broker) ? "" : frmlst.Broker.Trim().ToUpper()
}
equals new
{
val = String.IsNullOrEmpty(viewalllst.ViewAllSection) ? "" : viewalllst.ViewAllSection.Trim().ToUpper(),
val1 = String.IsNullOrEmpty(viewalllst.xFundCode) ? "" : viewalllst.xFundCode.Trim().ToUpper(),
val2 = String.IsNullOrEmpty(viewalllst.ViewAllPeriod) ? "" : viewalllst.ViewAllPeriod.Replace("A", "").Replace("E", "").Trim().ToUpper(),
val3 = String.IsNullOrEmpty(viewalllst.ViewAllBroker) ? "" : viewalllst.ViewAllBroker.Trim().ToUpper()
}
select new QCHelper()
{
Value = viewalllst == null ? string.Empty : (viewalllst.Value == null ? string.Empty : viewalllst.Value),
}).ToList<QCHelper>();
cfList & QCViewAllBrokerList1 these are two List<t> type. i am joining these two list and getting out of memory exception
i follow these two below links but there suggestion does not work for me.
https://stackoverflow.com/a/17322112/10839668
https://stackoverflow.com/a/53424048/10839668
please guide me how could i get rid of out of memory exception. thanks
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That query is such a dog breakfast that I'm not surprised it fails. You are probably creating the equivalent of an outer join and getting 800k * 800k records.
I would ask a couple of question of the requirements, why do you need 800k records in the client and how do you expect to use the collection when you have it.
If this was my problem I would create a view in the database to validate the joins and then select on the view with a filter (you cannot consume 800k record in the client).
Never underestimate the power of human stupidity -
RAH
I'm old. I know stuff - JSOP
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My question is .Net can not handle big data when run on 64 bit processor?
so many company work with huge data...how they handle it. as per our client requirement i have to work with xml file. we store data in xml not in db. this is client requirement.
any good suggestion please.
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Up until .NET 4.5, there was a hard limit on the size of any single object, which was 2GB. With .NET 4.5 and above, that limit ins't hard set any more. You can set an option in your apps App.Config file to remove that limit.
See With .NET 4.5, 10 years memory limit of 2 GB is over | Bahrudin Hrnjica Blog[^] for a short explanation.
But, you still have a problem. There is only ever so much memory in a machine. If your .XML file grows (and do NOT make the mistake of saying it never will!) you will eventually run out of memory, even on a 64-bit machine.
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Mou_kol wrote: so many company work with huge data...how they handle it.
By reading and updating parts of it.
Mou_kol wrote: this is client requirement.
The client might want that as an endresult, but doesn't care for intermediate stages. You can still mirror a copy on a database for quering 
Bastard Programmer from Hell 
If you can't read my code, try converting it here[^]
"If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
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Yes; it can handle it.
It's the "size of the data"; not the number of records that matters.
But since you never once mentioned "bytes", I would not assume that "number of records" is the issue.
Pre-process / pre-select / stage the input files (instead of in the join) if you want to gain any insight at all into "your data".
You gain nothing by trying to get one statement to do everything. LINQ is not "A.I."
The Master said, 'Am I indeed possessed of knowledge? I am not knowing. But if a mean person, who appears quite empty-like, ask anything of me, I set it forth from one end to the other, and exhaust it.'
― Confucian Analects
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Mou_kol wrote: any good suggestion please.
Either use a database like everyone else or get a new client.
Companies that have even small volumes of data almost all use a database, XML is a transport medium NOT a storage tool and even that has been replaced by JSON.
As others suggested if you must use linq then pre filter the records so you are working with a smaller data set.
Never underestimate the power of human stupidity -
RAH
I'm old. I know stuff - JSOP
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You're doing a "new" projection into two objects, doing all kinds of string manipulations which create new string objects, all to do a comparison across 800,000 records IN MEMORY, not on the SQL server, and you wonder why you get OutOfMemory exceptions?
I agree, that query is complete garbage and doesn't scale at all. You have to create a view in the database for this kind of work.
If you're doing a IsNullOrEmpty and Trim's and ToUpper's, your data is garbage to begin with and needs to be cleaned up before it ever gets into the database.
.
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As others have stated, doing this in a database is probably better. Databases are not magic though. Set it up wrong (lack of indexes, asking it to join with queries written as bad in SQL as these are written in Linq) and it will be crazy slow.
If it isn't possible to use a database I would do load the second lists into a lookup (if multiple records can have the same key) or dictionary (if you are sure they are unique.
Now the first list can do a "manual" join. Assuming you used a lookup (use .ToLookup or load directly to your own ILookup implementation) it will be something like (just written from memory, you will need to adapt it):
from leftItem in list1
let discustingKey = CalculateYourUglyKey(leftItem)
where list2Lookup.ContainsKey(discustingKey)
from rightItem in list2Lookup[discustingKey]
select WhateverYouWantToCreateFromLeftAndRightItem(leftItem, rightItem)
Sorry, I can't say how to format it exactly so it gives you the current output, because frankly your code is so ugly I can't read it - but this should give you an idea on how to reduce your key calculation to once per item in each list.
Instead of using Linq to make the "kind of a join", you can even do it from within an XML reader as each element is read. Then only the second list and the result needs to be in memory at the same time.
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your sample code not clear to me.can you please post a working small sample code using lookup what you have show me as sample. thanks
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Sorry, I am on holiday and I am not going to spend time on this. Try to google: linq tolookup
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hello,
I have this while loop
while (true)
{
Thread.Sleep(40);
if (Control.MouseButtons == MouseButtons.Left)
{
MessageBox.Show("Left");
}
if (Control.MouseButtons == MouseButtons.Right)
{
MessageBox.Show("Right");
}
I use this on threading to monitor the mouse button state any time without focus on particular
form.
I need make the same monitor to the mouse wheel, how I can do this in the same loop?
Thanks
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0: disclaimer: I am not informed about how the use of threading may come into play here.
1: don't use a 'while loop: it's going to degrade performance: what you need in this case is a 'hook to get all Mouse Events ... either for a Form (WndProc), or for your app (App) ... or, for every running process (global).
2: why you need a 'hook: only the Control with Focus gets the WM_MOUSEWHEEL message; you can define an EventHandler to get the 'MouseWheel status:
private void Form1_Load(object sender, EventArgs e)
{
this.MouseWheel += OnMouseWheel;
}
private int lastMWDelta;
private int lastMWClicks;
public Point lastMWPt;
public Control lastMWActiveControl;
private void OnMouseWheel(object sender, MouseEventArgs e)
{
lastMWDelta = e.Delta;
lastMWClicks = e.Clicks;
lastMWPt = e.Location;
lastMWActiveControl = sender as Control;
Console.WriteLine($"wheel: control: {lastMWActiveControl.Name} delta: {lastMWDelta}");
}If there are only specific Controls you want to get wheel events for: define the same type of EventHandler for those.
3: how do you implement a 'hook ?
a: first decide what type of 'hook is required.
b: read the articles here on CodeProject about 'hooks ... like: [^], [^], [^], [^]
Come back with code, and specific issues, or questions.
«Where is the Life we have lost in living? Where is the wisdom we have lost in knowledge? Where is the knowledge we have lost in information?» T. S. Elliot
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Can anyone provide an example, or point me to a walkthrough?
I need clarification on how to make a sql table(SQL Express) using code first approach in entity framework model and:(add, edit, save & delete) in that table, and to do that using MVVM pattern, in a WPF application.
Specifically I am facing a problem in trying to create the database using the c# code in the wpf application without having to access the SQl Server Management Studio to create the database.
I would really appreciate any advice.
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You're not going to find a walkthrough with all of those things, you need to break the problem down. If your issue is creating a DB using code first then google for a solution to that. That solution will work regardless of if it is a console app, a website or a WPF application.
create database ef code first - Google Search[^]
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i know the basic method but i am having problems in finding exact syntax for my requirement .i have done extensive searches in google.I was hoping for more specific resources
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