I was trying to make Custom paging with LINQ. Everything is fine. But the Last page results previous page output values. I know because of this,
int skip = Math.Max(AC.rows * (AC.page - 1), 0); // Doing page -1.
But I need to know how can i make the logic purely to work with pagination. Pls someone guide me to do correct logic for this.
Code
var selectpending = CsA.CsAutoCompletes(AC, searchTerm);
var Tot = selectpending.Count();
int skip = Math.Max(AC.rows * (AC.page - 1), 0);
int totpages = Convert.ToInt32(Tot / AC.rows);
um = selectpending.Skip(skip).Take(AC.rows).ToList();
return Json(new
{
rows = um,
records = Tot,
page = AC.page,
total = totpages
}
, JsonRequestBehavior.AllowGet);
Tot may not be divisible by AC.Rows, so you should do something like int totpages = (int)Math.Ceiling(((double)Tot)/ AC.Rows);
Related
I am not able to fetch a max value from a number field in AppMaker. The field is filled with unique integers from 1 and up. In SQL I would have asked like this:
SET #tKey = (SELECT MAX(ID) FROM GiftCard);
In AppMaker I have done the following (with a bit help from other contributors in this forum) until now, and it returns tKey = "NaN":
var tKey = google.script.run.MaxID();
function MaxID() {
var ID_START_FROM = 11000;
var lock = LockService.getScriptLock();
lock.waitLock(3000);
var query = app.models.GiftCard.newQuery();
query.sorting.ID._descending();
query.limit = 1;
var records = query.run();
var next_id = records.length > 0 ? records[0].ID : ID_START_FROM;
lock.releaseLock();
return next_id;
}
There is also a maxValue() function in AppMaker. However, it seems not to work in that way I use it. If maxvalue() is better to use, please show :-)
It seems that you are looking in direction of auto incremented fields. The right way to achieve it would be using Cloud SQL database. MySQL will give you more flexibility with configuring your ids:
ALTER TABLE GiftCard AUTO_INCREMENT = 11000;
In case you strongly want to stick to Drive Tables you can try to fix your script as follow:
google.script.run
.withSuccessHandler(function(maxId) {
var tKey = maxId;
})
.withFailureHandler(function(error) {
// TODO: handle error
})
.MaxID();
As a side note I would also recommend to set your ID in onBeforeCreate model event as an extra security layer instead of passing it to client and reading back since it can be modified by malicious user.
You can try using Math.max(). Take into consideration the example below:
function getMax() {
var query = app.models.GiftCard.newQuery();
var allRecords = query.run();
allIds = [];
for( var i=0; i<allRecords.length;i++){
allIds.push(allRecords[i].ID);
}
var maxId = Math.max.apply(null, allIds);
return maxId;
}
Hope it helps!
Thank you for examples! The Math.max returned an undefined value. Since this simple case is a "big" issue, I will solve this in another way. This value is meant as a starting value for a sequence only. An SQL base is better yes!
I'm trying to create a chess game for Android and would like to avoid having to declare every button when they are all named so similarly. I tried to generate all of the A + Num button using this for loop.
int RowNum ;
for (RowNum = 1; RowNum < 8; RowNum++) {
String Position = "A" + RowNum;
Button Position = (Button)findViewById(R.id.Position);
}
But I have an error: Variable 'Position' is already defined in the scope.
I would really appreciate if someone could explain to me the best way to go about doing this.
Thanks in advance.
R.Id.A1, R.id.A2, etc. are identifiers and each of them is mapped to a single integer during compilation of R class. Thus, you cannot manipulate the 'R.id.sth' as a string because it will not compile properly.
A way to solve that is search for the string in resources dynamically with a code like this:
Button[] buttons=new Button[8];
for(int RowNum=0; RowNum<8; RowNum++) {
String buttonID = "A"+(RowNum+1);
int resID = getResources().getIdentifier(buttonID, "id", getPackageName());
buttons[RowNum] = ((Button) findViewById(resID));
}
Alternatively, to avoid the time overhead of dynamic search you can add a resource array:
int[] butIds = {R.id.A1, R.id.A2,...};
Button[] buttons= new Button[8];
for(int RowNum=0; RowNum<8, RowNum++) {
buttons[RowNum]= ((Button) findViewById(butIds[RowNum]));
}
You can even store the resource array in XML form and retrieve it as a TypedArray.
You called your String and Button object both Position. Give them different names, e.g.
for (int RowNum = 1; RowNum < 8; RowNum++) {
String currentPosition = "A" + RowNum;
//Why doesn this not use the Position (now 'currentPosition' variable)?
Button currentButton = (Button)findViewById(R.id.Position);
}
Semantically I still don't get that piece of code because Position is not used within the argument of findViewById, to which you pass a static variable R.id.Position.
I want to extract part of a collection to another collection.
I can easily do the same using a for loop, but my linq query is not working for the same.
I am a neophyte in Linq, so please help me correcting the query (if possible with explanation / beginners tutorial link)
Legacy way of doing :
Collection<string> testColl1 = new Collection<string> {"t1", "t2", "t3", "t4"};
Collection<string> testColl2 = new Collection<string>();
for (int i = 0; i < newLength; i++)
{
testColl2.Add(testColl1[i]);
}
Where testColl1 is the source & testColl2 is the desired truncated collection of count = newLength.
I have used the following linq queries, but none of them are working ...
var result = from t in testColl1 where t.Count() <= newLength select t;
var res = testColl1.Where(t => t.Count() <= newLength);
Use Enumerable.Take:
var testColl2 = testColl1.Take(newLength).ToList();
Note that there's a semantic difference between your for loop and the version using Take. The for loop will throw with IndexOutOfRangeException exception if there are less than newLength items in testColl1, whereas the Take version will silently ignore this fact and just return as many items up to newLength items.
The correct way is by using Take:
var result = testColl1.Take(newLength);
An equivalent way using Where is:
var result = testColl1.Where((i, item) => i < newLength);
These expressions will produce an IEnumerable, so you might also want to attach a .ToList() or .ToArray() at the end.
Both ways return one less item than your original implementation does because it is more natural (e.g. if newLength == 0 no items should be returned).
You could convert to for loop to something like this:
testColl1.Take(newLength)
Use Take:
var result = testColl1.Take(newLength);
This extension method returns the first N elements from the collection where N is the parameter you pass, in this case newLength.
I have a linq query like this:
var accounts =
from account in context.Accounts
from guranteer in account.Gurantors
where guranteer.GuarantorRegistryId == guranteerRegistryId
select new AccountsReport
{
recordIndex = ?
CreditRegistryId = account.CreditRegistryId,
AccountNumber = account.AccountNo,
}
I want to populate recordIndex with the value of current row number in collection returned by the LINQ. How can I get row number ?
Row number is not supported in linq-to-entities. You must first retrieve records from database without row number and then add row number by linq-to-objects. Something like:
var accounts =
(from account in context.Accounts
from guranteer in account.Gurantors
where guranteer.GuarantorRegistryId == guranteerRegistryId
select new
{
CreditRegistryId = account.CreditRegistryId,
AccountNumber = account.AccountNo,
})
.AsEnumerable() // Moving to linq-to-objects
.Select((r, i) => new AccountReport
{
RecordIndex = i,
CreditRegistryId = r.CreditRegistryId,
AccountNumber = r.AccountNo,
});
LINQ to objects has this builtin for any enumerator:
http://weblogs.asp.net/fmarguerie/archive/2008/11/10/using-the-select-linq-query-operator-with-indexes.aspx
Edit: Although IQueryable supports it too (here and here) it has been mentioned that this does unfortunately not work for LINQ to SQL/Entities.
new []{"aap", "noot", "mies"}
.Select( (element, index) => new { element, index });
Will result in:
{ { element = aap, index = 0 },
{ element = noot, index = 1 },
{ element = mies, index = 2 } }
There are other LINQ Extension methods (like .Where) with the extra index parameter overload
Try using let like this:
int[] ints = new[] { 1, 2, 3, 4, 5 };
int counter = 0;
var result = from i in ints
where i % 2 == 0
let number = ++counter
select new { I = i, Number = number };
foreach (var r in result)
{
Console.WriteLine(r.Number + ": " + r.I);
}
I cannot test it with actual LINQ to SQL or Entity Framework right now. Note that the above code will retain the value of the counter between multiple executions of the query.
If this is not supported with your specific provider you can always foreach (thus forcing the execution of the query) and assign the number manually in code.
Because the query inside the question filters by a single id, I think the answers given wont help out. Ofcourse you can do it all in memory client side, but depending how large the dataset is, and whether network is involved, this could be an issue.
If you need a SQL ROW_NUMBER [..] OVER [..] equivalent, the only way I know is to create a view in your SQL server and query against that.
This Tested and Works:
Amend your code as follows:
int counter = 0;
var accounts =
from account in context.Accounts
from guranteer in account.Gurantors
where guranteer.GuarantorRegistryId == guranteerRegistryId
select new AccountsReport
{
recordIndex = counter++
CreditRegistryId = account.CreditRegistryId,
AccountNumber = account.AccountNo,
}
Hope this helps.. Though its late:)
How do you page through a collection in LINQ given that you have a startIndex and a count?
It is very simple with the Skip and Take extension methods.
var query = from i in ideas
select i;
var paggedCollection = query.Skip(startIndex).Take(count);
A few months back I wrote a blog post about Fluent Interfaces and LINQ which used an Extension Method on IQueryable<T> and another class to provide the following natural way of paginating a LINQ collection.
var query = from i in ideas
select i;
var pagedCollection = query.InPagesOf(10);
var pageOfIdeas = pagedCollection.Page(2);
You can get the code from the MSDN Code Gallery Page: Pipelines, Filters, Fluent API and LINQ to SQL.
I solved this a bit differently than what the others have as I had to make my own paginator, with a repeater. So I first made a collection of page numbers for the collection of items that I have:
// assumes that the item collection is "myItems"
int pageCount = (myItems.Count + PageSize - 1) / PageSize;
IEnumerable<int> pageRange = Enumerable.Range(1, pageCount);
// pageRange contains [1, 2, ... , pageCount]
Using this I could easily partition the item collection into a collection of "pages". A page in this case is just a collection of items (IEnumerable<Item>). This is how you can do it using Skip and Take together with selecting the index from the pageRange created above:
IEnumerable<IEnumerable<Item>> pageRange
.Select((page, index) =>
myItems
.Skip(index*PageSize)
.Take(PageSize));
Of course you have to handle each page as an additional collection but e.g. if you're nesting repeaters then this is actually easy to handle.
The one-liner TLDR version would be this:
var pages = Enumerable
.Range(0, pageCount)
.Select((index) => myItems.Skip(index*PageSize).Take(PageSize));
Which can be used as this:
for (Enumerable<Item> page : pages)
{
// handle page
for (Item item : page)
{
// handle item in page
}
}
This question is somewhat old, but I wanted to post my paging algorithm that shows the whole procedure (including user interaction).
const int pageSize = 10;
const int count = 100;
const int startIndex = 20;
int took = 0;
bool getNextPage;
var page = ideas.Skip(startIndex);
do
{
Console.WriteLine("Page {0}:", (took / pageSize) + 1);
foreach (var idea in page.Take(pageSize))
{
Console.WriteLine(idea);
}
took += pageSize;
if (took < count)
{
Console.WriteLine("Next page (y/n)?");
char answer = Console.ReadLine().FirstOrDefault();
getNextPage = default(char) != answer && 'y' == char.ToLowerInvariant(answer);
if (getNextPage)
{
page = page.Skip(pageSize);
}
}
}
while (getNextPage && took < count);
However, if you are after performance, and in production code, we're all after performance, you shouldn't use LINQ's paging as shown above, but rather the underlying IEnumerator to implement paging yourself. As a matter of fact, it is as simple as the LINQ-algorithm shown above, but more performant:
const int pageSize = 10;
const int count = 100;
const int startIndex = 20;
int took = 0;
bool getNextPage = true;
using (var page = ideas.Skip(startIndex).GetEnumerator())
{
do
{
Console.WriteLine("Page {0}:", (took / pageSize) + 1);
int currentPageItemNo = 0;
while (currentPageItemNo++ < pageSize && page.MoveNext())
{
var idea = page.Current;
Console.WriteLine(idea);
}
took += pageSize;
if (took < count)
{
Console.WriteLine("Next page (y/n)?");
char answer = Console.ReadLine().FirstOrDefault();
getNextPage = default(char) != answer && 'y' == char.ToLowerInvariant(answer);
}
}
while (getNextPage && took < count);
}
Explanation: The downside of using Skip() for multiple times in a "cascading manner" is, that it will not really store the "pointer" of the iteration, where it was last skipped. - Instead the original sequence will be front-loaded with skip calls, which will lead to "consuming" the already "consumed" pages over and over again. - You can prove that yourself, when you create the sequence ideas so that it yields side effects. -> Even if you have skipped 10-20 and 20-30 and want to process 40+, you'll see all side effects of 10-30 being executed again, before you start iterating 40+.
The variant using IEnumerable's interface directly, will instead remember the position of the end of the last logical page, so no explicit skipping is needed and side effects won't be repeated.