I have an empty list accepting string values.
When an element will be added I need to check if a string with the same value already exist in the list, if yes an exception should occur (ROLE 1 only unique value in the array).
Now I would like a user lets edit element in the list, if the new edited value is unique fine, otherwise an exception should occur.
My problem is: let's imagine the user select the edit element but actually does not change the value when sending to the server. The system should detect that the element has not being changed and accept the value (even if is already present in the list).
PS I simplificate the problem, I'm actually using MVC and EF & linq. My problem is that I cannot check if the value inserted has been edited or not in the interface of my application.
Could you help me out to find an effective algo to solve this problem? Thanks
Let me know if the question is enough clear or you need more information
This is my solution:
Let the client check if the text was modified. If not, tell the server there was no modification. If this is not possible have the client send both the orinigial text and the modified text, and then the server will be able to check if it was modified. (if it wasn't then there is no need to touch the data you are storing). This applies for both desktop and web enviroments.
Preferibly don't use a list, use a set (may be a hashset). The set will only allow to have each item once. In case you can't I guess you can continue using the list. If I understand correctly you are using a database, so if you could interface with the database engine directly instead of syncing the list (or set) your application will have a performance boost.
Convert the edition of the list/set into a add-remove pair (instead of setting the item). Have it check if the list/set contains the new value before doing any modification. If the new value is already present then you can throw an exception or send a message to the client (or whatever is more appropiate for your enviroment).
You may want to sync the access to your list/set, keep it simple: use a lock (Monitor). I would consider a read-write lock, but that is complicating things while you are learning. [If you interface directly with the database engine, you can let it handle that instead]. Note: there is no need for this if you will only have one single client... ever (unless that single client can send multiple concurrent requests... :P).
Related
I have a situation wherein a List object is built off of values pulled from a MSSQL database. However, this particular table is mysteriously getting an errant record or two tossed in. Removing the records cause trouble even though they have no referential links to any other tables, and will still get recreated without any known user actions taken. This causes some trouble as it puts unwanted values on display that add a little bit of confusion. The specific issue is that this is a platform that allows users to run a search for quotes, and the filtering allows for sales rep selection. The select/dropdown field is showing these errant values, and they need to be removed.
Given that deleting the offending table rows does not provide a desirable result, I was thinking that maybe the best course of action was to modify the code where the List object is created and either filter the values out or remove them after the object is populated. I'd like to do this in a clean, scalible fashion by providing some kind of appendable data object where I could just add in a new string value if something else cropped up as opposed to doing something clunky that adds new code to find the value and remove it each time.
My thought was to create a string array, and somehow loop through that to remove bad List values, but I wasn't entirely certain that was the best way to approach this, and I could not for the life of me think of a clean approach for this. I would think that the best way would be to add a filter within the Find arguments, but I don't know how to add in an array or list that way. Otherwise I figured to loop through the values either before or after the sorting of the List and remove any matches that way, but I wasn't sure that was the best choice of actions.
I have attached the current code, and would appreciate any suggestions.
int licenseeID = Helper.GetLicenseeIdByLicenseeShortName(Membership.ApplicationName);
List<User> listUsers;
if (Roles.IsUserInRole("Admin"))
{
//get all users
listUsers = User.Find(x => x.LicenseeID == licenseeID).ToList();
}
else
{
//get only the current user
listUsers = User.Find(x => (x.LicenseeID == licenseeID && x.EmailAddress == Membership.GetUser().Email)).ToList();
}
listUsers.Sort((x, y) => string.Compare(x.FirstName, y.FirstName));
-- EDIT --
I neglected to mention that I did not develop this, I merely inherited its maintenance after the original developer(s) disappeared, and my coworker who was assigned to it left the company. I'm not really really skilled at handling ASP.NET sites. Many object sources are hidden and unavailable for edit, I assume due to them being defined in a DLL somewhere. So, for any of these objects that are sourced from database tables, altering the tables will not help, since I would not be able to get the new data anyway.
However, I did try to do the following to filter out the undersirable data:
List<String> exclude = new List<String>(new String[] { "value1" , "value2" });
listUsers = User.Find(x => x.LicenseeID == licenseeID && !exclude.Contains(x.FirstName)).ToList();
Unfortunately it only resulted in an error being displayed to the page.
-- EDIT #2 --
I got the server setup to accept a new event viewer source so I could write info to the Application log to see what was happening. Looks like this installation of ASP.NET does not accept "Contains" as an action on a List object. An error gets kicked out stating that the method is not available.
I will probably add a bit to the table and flag Errant rows and then skip them when I query the table, something like
&& !ErrantData
Other way, that requires a bit more upkeep but doesn't require db change, would be to keep a text file that gets periodically updated and you read it and remove users from list based on it.
The bigger issue is unknown rows creeping in your database. Changing user credentials and adding creation timestamps may help you narrow down the search scope.
In MongoDB, accessing from C# driver:
I want to keep a list of keys (ints are fine), that have a current value. (Dictionary<int,int>) works well for the concept)
I need to have multiple (10+) machines setting values in this Document. Multiple threads on each machine.
Using C# and the MongoDB driver I need to:
If the key exists, increment the value for that key.
If it does not exist, I need to Add it, and set the value to 1.
Critically Important:
It can't overwrite values others are writing (I.E. No get doc and call Save() to save it)
It has to handle adding values that don't already exist gracefully.
I might be able to have a query that inserts a new document with all of the keys set to values of 0 - if this would help, but it won't be easy, so that is not a preferred answer.
I've tried using a Dictionary, and can't seem to figure out how to update it without it creating:
null,
{ v=1}
On my insert (which doesn't include the k=, and has the null, that I don't want. and causes deserialization to blow)
I don't care what method of serialization is used for the dictionary, and am open to any other method of storage.
Any ideas?
My best guess so far is to keep a list of keys that is separate from the values (two List and append the key to the key list if it isn't found, requery the list and use the first one as the index in the 2nd list. (This seems like it might have concurrency issues that could be hard to track down.)
I would prefer the Linq syntax, but am open to using the .Set (string,value) syntax if that makes things work.
We are creating a client server application using WPF/C# with SQL. Here we are generating a unique number b checking DB(To get the last maximum number) and with that max value, we are increment '1' and storing the value in DB. At this time another user also working on the same screen and creating unique numbers, in some case the the unique numbers gets duplicated and throws exception.
We found this is a concurrency issue.
Indeed, fetching a number out, adding one, and hoping it still isn't in use is a thread-race and a race between multiple clients - and should be avoided.
Options:
use an IDENTITY column in the database, and let the database generate the value itself during INSERT; the database server knows how to do this safely and reliably
if that isn't possible, you might want to delay this code until you are ready to INSERT so it is all part of a single database operation - and even then, if it isn't in a "serializable transaction" (with key-range read locks, etc), then you would have to loop on "get the max, increment, try to insert but note that we might have lost a race, so only insert if the value doesn't exist - which it might; repeat from start if unsuccessful"
alternatively, you could create the new record when you first need the number (even though the rest of the data isn't available), noting that you might still need the "loop until successful" approach
Frankly, the IDENTITY column approach is the simplest.
Finally, We have follwed Singleton pattern with lock to resolver this issue.
Thanks.
I have an ASP.Net form and I want to send an email when the user changes their data. The email should only include data that has changed, and there are about 15 data fields total.
I don't want to use an ORM since I am updating a website that a 3rd party built for us, and all their data access calls go through a custom library of theirs.
The only ways to do this I can think of is
Make another database call to get old values and compare the form values one-by-one. If they're different, append to the email.
Store original data somewhere when it's first loaded (hidden field, session, etc), and once again compare the data one field at a time and append the differences to an email
Have someone on SO tell me there's an easier and/or simpler way that I haven't thought of
All the text boxes will have a TextChanged event, you can have them mark themselves as modified. ComboBox's will have a SelectedIndexChanged event, and so on.
Edit: All changed events can check their initial values (even on reverted changes) and either mark themselves as still modified or on a revert, as un-modified.
Here are some suggestions that may / may not be useful:
Trigger on the database table and the trigger compares the old (using the DELETED table) and updated (using the INSERTED table) and then sends an email. This may or may not be viable and I am not a big advocate of triggers.
Like you have already said you could make another database call, which would be my reccommended approach.
From what you've said I think that the only way forward is to create a duplicate dataset on the form to store the old data and run a comparison at the point where you want to produce the email.
You can use Dataset.Copy to copy structure and data.
However, now that I think about it there's always the Datset.GetChanges() method and the Dataset.AcceptChanges() along with DataSet.HasChanges()
Example code from this link:
if(dataSet.HasChanges(DataRowState.Modified |
DataRowState.Added)&& dataSet.HasErrors)
{
// Use GetChanges to extract subset.
changesDataSet = dataSet.GetChanges(
DataRowState.Modified|DataRowState.Added);
PrintValues(changesDataSet, "Subset values");
// Insert code to reconcile errors. In this case, reject changes.
foreach(DataTable changesTable in changesDataSet.Tables)
{
if (changesTable.HasErrors)
{
foreach(DataRow changesRow in changesTable.Rows)
{
//Console.WriteLine(changesRow["Item"]);
if((int)changesRow["Item",DataRowVersion.Current ]> 100)
{
changesRow.RejectChanges();
changesRow.ClearErrors();
}
}
}
}
// Add a column to the changesDataSet.
changesDataSet.Tables["Items"].Columns.Add(
new DataColumn("newColumn"));
PrintValues(changesDataSet, "Reconciled subset values");
// Merge changes back to first DataSet.
dataSet.Merge(changesDataSet, false,
System.Data.MissingSchemaAction.Add);
}
PrintValues(dataSet, "Merged Values");
I'm creating a database where users can enter some Error Reports and we can view them. I'm making these database with C# in the ASP MVC 3 .NET framework (as the tags imply). Each Error Report has a unique ID, dubbed ReportId, thus none of them are stored under the same Id. However, whenever a User creates a new Error, I pass their User Name and store it in with the rest of the report (I use User.Identity.Name.ToString() to get their name and store it as a string). I know how to get a single item from the data using a lambda expression, like so:
db.DBSetName.Single(g => g.Name == genre)
The above code is based on an MVC 3 tutorial (The Movie Store one) provided by ASP. This was how they taught me how to do it.
My major question is: is there a member function like the .Single one that will parse through the whole database and only output database entries whose stored User Name matches that of the currently logged in user's? Then, I can use this to restrict User's to being only able to edit their own entries, since only their entries would be passed to the User's View.
What would be the best way to implement this? Since the ReportId will not be changed, a new data structure can be created to store the user's Errors and passed through to the Index (or Home) View of that particular controller. From there they should be able to click any edit link, which will pass the stored ReportId back to the Edit Action of this particular controller, which can then search the entire database for it. Am I right in assuming this would work? And would this be ideal, given that the other items in the database are NOT passed through to the Index in this method, meaning the User does not have access to the other items' ReportId's, which the user needs to pass into the Edit Action for it to work? If this is ideal, this is the method that requires me to know how to parse through a database and grab every element that fits a particular description (stored User Name matches User's current User Name).
Or would a better approach be to pass the whole database to the Index View and only output the database entries that have User Name values that match the current logged in user's? I guess this could be done in a foreach loop with a nested if loop, like so:
#foreach(var item in db.Reports)
{
if(item.UserName == User.Identity.Name.ToString())
{
...code to output table...
}
}
But this passes the whole database which gives the user a lot more info than they need. It also gives them potential access to info I don't want them to have. However, I don't have to make a new data structure or database, which should lower server memory usage and fetch time, right? Or are databases passed by copy? If so, this method seems kinda dumb. However, I don't know if the first method would fracture the database potentially, this one certainly would not. Also don't remember if I NEED an else statement in C#, I'm more familiar with C++, where you don't need one and you also don't need {}'s for single line if's, if I need one: please don't judge me too harshly on it!
Small note: I am using CRUD Controllers made with the Entity First Framework in order to edit my database. As such, all creation, reading, updating, and deletion code has been provided for me. I have chosen not to add such basic, common code. If it is needed, I can add it. I will add what the Edit Action looks like:
public ActionResult Edit(string id)
{
Report report = db.Reports.Find(id);
return View(report);
}
It accepts a string as an id, ReportId is the id used and it IS a string. It is a randomly generated GUID string made with the GUID.NewGuid().ToString() function. I will also be doing the comparison of names with:
Model.UserName == User.Identity.Name.ToString()
Which was shown earlier. Sorry if this is too much text, I wanted to provide as much info as possible and not make anyone mad. If more info is needed, it can certainly be provided. So at the end of the post, the major question actually comes down to: which of the above two methods is best? And, if it's the first one, how do I implement something like that?
Thanks for your help!
Unless I'm completely misunderstanding you, you just want .Where()
Like this:
var reports = db.Reports.Where(r => r.genre == inputGenre);
This would get you an IEnumerable of Report, which you could then use however you wish.