I'm trying to work with a LINQ result set of 4 tables retrieved with html agility pack. I'd like to process each one slightly differently by setting a variable for each (switch statement below), and then processing the rows within the table. The variable would ideally be the index for each of the tables in the set, 0 to 3, and would be used in the switch statement and to select the rows. I haven't been able to locate the index property, but I see it used in situations such as SelectChildNode.
My question is can I refer to items within a LINQ result set by index? My "ideal scenario" is the last commented out line. Thanks in advance.
var ratingsChgs = from table in htmlDoc.DocumentNode
.SelectNodes("//table[#class='calendar-table']")
.Cast<HtmlNode>()
select table;
String rtgChgType;
for (int ratingsChgTbl = 0; ratingsChgTbl < 4; ratingsChgTbl++)
{
switch (ratingsChgTbl)
{
case 0:
rtgChgType = "Upgrades";
break;
case 1:
rtgChgType = "Downgrades";
break;
case 2:
rtgChgType = "Coverage Initiated";
break;
case 3:
rtgChgType = "Coverage Reit/ Price Tgt Changed";
break;
//This is what I'd like to do.
var tblRowsByChgType = from row in ratingsChgs[ratingsChgTbl]
.SelectNodes("tr")
select row;
//Processing of returned rows.
}
}
ElementAt does what you're asking for. I don't recommend using it in your example, though, because each time you call it, your initial LINQ query will be executed. The easy fix is to have ratingsChgs be a List or Array.
You can also refactor out the switch statement. It is overkill when you only need to iterate through a list of items. Here is a possible solution:
var ratingsChgs = from table in htmlDoc.DocumentNode
.SelectNodes("//table[#class='calendar-table']")
.Cast<HtmlNode>()
select table;
var rtgChgTypeNames = new List
{
"Upgrades",
"Downgrades",
"Coverage Initiated",
"Coverage Reit/ Price Tgt Changed"
};
var changeTypes = ratingsChgs.Zip(rtgChgTypeNames, (changeType, name) => new
{
Name = name,
Rows = changeType.SelectNodes("tr")
});
foreach( var changeType in changeTypes)
{
var name = changeType.Name;
var rows = changeType.Rows;
//Processing of returned rows.
}
Also, why not store your rating change types in the HTML doc? It seems odd to have table information defined in the business logic.
Related
My Interactive Grid has column caled "EMPL_STAT1".
I use the code below to get the return value of the select list from selected record.
Works fine but I was wondering how to change that code to get the return value of the select list from each record (not selected only) in "EMPL_STAT1" column?
Could you give me any advice?
var reg = apex.region('ig_emp').widget();
var grid = reg.interactiveGrid("getViews","grid");
var model = reg.interactiveGrid("getViews","grid").model;
var selectedRecords = grid.getSelectedRecords();
for (i = 0; i < selectedRecords.length; i++)
{
record = model.getRecord(selectedRecords[i][0]);
itemcodeField = model.getFieldKey("EMPL_STAT1");
alert(record[itemcodeField].v);
}
The Javascript you shared, gets the selected row records only.
Let's say my IG's static ID is igTest
var model = apex.region("igTest").widget().interactiveGrid("getViews", "grid").model;
model.forEach(function(igrow) {
console.log(igrow[model.getFieldKey("FIRST_NAME")]);
});
This will loop through all the records in the IG.
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 have a an array of objects that I want to enter into the database.
My method call looks like this.
public void Add(CardElement[] cardElements){
foreach (var cardElement in cardElements)
{
Data.Entry(cardElement).State = System.Data.EntityState.Added;
}
Data.SaveChanges();
}
The database table resembles this
MS SQL = Table mytable Columns a,b,c,d,e,f
Unique Constraint a,b,c
The data I want to insert resembles this.
var obj [] = new [] {
new MyObject () { a = 1, b =1, c = 1 },
new MyObject () { a = 1, b =1, c = 2 }
new MyObject () { a = 1, b =1, c = 3 }
};
So, I want to check the database for these three rows before I add them to the database.
I could do something like but I assume this should cause some extra trips to the database.
private bool checkExists()...
foreach (var cardElement in cardElements)
{
var exists = (from ce in Data.CardElements
where ce.CardId == cardElement.CardId
where ce.Area == cardElement.Area
where ce.ElementName == cardElement.ElementName
select ce).Any();
if(exists return true)
}
return false
So, how could I handle this more gracefully?
Is it even worth trying to accomplish this using linq?
Should I write some stored procedures for performance?
I agree that you should let the db make the decision.
Please have a look at using UPSERT as stated in this post
Why not just attempt the insert and let the database tell you if any unique constraint violations have occurred (using try/catch)?
The problem is that even if you query data somebody else can insert the record between your query and saving changes. You will still have to handle exception for violating unique constraint despite your additional queries - and yes, every check will do additional trip to database.
If your main concern is performance use stored procedure where you can additionally use table hint to lock table for inserts during initial check for existence.
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:)
I ran into a scenario where LINQ to SQL acts very strangely. I would like to know if I'm doing something wrong. But I think there is a real possibility that it's a bug.
The code pasted below isn't my real code. It is a simplified version I created for this post, using the Northwind database.
A little background: I have a method that takes an IQueryable of Product and a "filter object" (which I will describe in a minute). It should run some "Where" extension methods on the IQueryable, based on the "filter object", and then return the IQueryable.
The so-called "filter object" is a System.Collections.Generic.List of an anonymous type of this structure: { column = fieldEnum, id = int }
The fieldEnum is an enum of the different columns of the Products table that I would possibly like to use for the filtering.
Instead of explaining further how my code works, it's easier if you just take a look at it. It's simple to follow.
enum filterType { supplier = 1, category }
public IQueryable<Product> getIQueryableProducts()
{
NorthwindDataClassesDataContext db = new NorthwindDataClassesDataContext();
IQueryable<Product> query = db.Products.AsQueryable();
//this section is just for the example. It creates a Generic List of an Anonymous Type
//with two objects. In real life I get the same kind of collection, but it isn't hard coded like here
var filter1 = new { column = filterType.supplier, id = 7 };
var filter2 = new { column = filterType.category, id = 3 };
var filterList = (new[] { filter1 }).ToList();
filterList.Add(filter2);
foreach(var oFilter in filterList)
{
switch (oFilter.column)
{
case filterType.supplier:
query = query.Where(p => p.SupplierID == oFilter.id);
break;
case filterType.category:
query = query.Where(p => p.CategoryID == oFilter.id);
break;
default:
break;
}
}
return query;
}
So here is an example. Let's say the List contains two items of this anonymous type, { column = fieldEnum.Supplier, id = 7 } and { column = fieldEnum.Category, id = 3}.
After running the code above, the underlying SQL query of the IQueryable object should contain:
WHERE SupplierID = 7 AND CategoryID = 3
But in reality, after the code runs the SQL that gets executed is
WHERE SupplierID = 3 AND CategoryID = 3
I tried defining query as a property and setting a breakpoint on the setter, thinking I could catch what's changing it when it shouldn't be. But everything was supposedly fine. So instead I just checked the underlying SQL after every command. I realized that the first Where runs fine, and query stays fine (meaning SupplierID = 7) until right after the foreach loop runs the second time. Right after oFilter becomes the second anonymous type item, and not the first, the 'query' SQL changes to Supplier = 3. So what must be happening here under-the-hood is that instead of just remembering that Supplier should equal 7, LINQ to SQL remembers that Supplier should equal oFilter.id. But oFilter is a name of a single item of a foreach loop, and it means something different after it iterates.
I have only glanced at your question, but I am 90% sure that you should read the first section of On lambdas, capture, and mutability (which includes links to 5 similar SO questions) and all will become clear.
The basic gist of it is that the variable oFilter in your example has been captured in the closure by reference and not by value. That means that once the loop finishes iterating, the variable's reference is to the last one, so the value as evaluated at lambda execution time is the final one as well.
The cure is to insert a new variable inside the foreach loop whose scope is only that iteration rather than the whole loop:
foreach(var oFilter in filterList)
{
var filter = oFilter; // add this
switch (oFilter.column) // this doesn't have to change, but can for consistency
{
case filterType.supplier:
query = query.Where(p => p.SupplierID == filter.id); // use `filter` here
break;
Now each closure is over a different filter variable that is declared anew inside of each loop, and your code will run as expected.
Working as designed. The issue you are confronting is the clash between lexical closure and mutable variables.
What you probably want to do is
foreach(var oFilter in filterList)
{
var o = oFilter;
switch (o.column)
{
case filterType.supplier:
query = query.Where(p => p.SupplierID == o.id);
break;
case filterType.category:
query = query.Where(p => p.CategoryID == o.id);
break;
default:
break;
}
}
When compiled to IL, the variable oFilter is declared once and used multiply. What you need is a variable declared separately for each use of that variable within a closure, which is what o is now there for.
While you're at it, get rid of that bastardized Hungarian notation :P.
I think this is the clearest explanation I've ever seen: http://blogs.msdn.com/ericlippert/archive/2009/11/12/closing-over-the-loop-variable-considered-harmful.aspx:
Basically, the problem arises because we specify that the foreach loop is a syntactic sugar for
{
IEnumerator<int> e = ((IEnumerable<int>)values).GetEnumerator();
try
{
int m; // OUTSIDE THE ACTUAL LOOP
while(e.MoveNext())
{
m = (int)(int)e.Current;
funcs.Add(()=>m);
}
}
finally
{
if (e != null) ((IDisposable)e).Dispose();
}
}
If we specified that the expansion was
try
{
while(e.MoveNext())
{
int m; // INSIDE
m = (int)(int)e.Current;
funcs.Add(()=>m);
}
then the code would behave as expected.
The problem is that you're not appending to the query, you're replacing it each time through the foreach statement.
You want something like the PredicateBuilder - http://www.albahari.com/nutshell/predicatebuilder.aspx