As per this link :http://msdn.microsoft.com/en-us/library/bb397906.aspx
namespace Linq
{
class IntroToLINQ
{
static void Main()
{
// The Three Parts of a LINQ Query:
// 1. Data source.
int[] numbers = new int[7] { 0, 1, 2, 3, 4, 5, 6 };
// 2. Query creation.
// numQuery is an IEnumerable<int>
var numQuery =
from num in numbers
where (num % 2) == 0
select num;
// 3. Query execution.
foreach (int num in numQuery)
{
Console.Write("{0,1} ", num);
}
}
}
}
It states that query will not be exeucted , until data is iterated through foreach. But when I debugged , the data memeber of var(resultviews) contains the result values before the execution of foreach. Why this is happening?
Because your debugger is executing the query for you.
Linq is using something that is called Deferred Execution. Here is a good blog post that explains it: LINQ and Deferred Execution.
When you first execute the iterator, the query is processed and executed (in memory, to a database or in another way). Your debugger will do this for you.
Take for example the following code (you can paste this in a Console Application):
using System;
using System.Diagnostics;
using System.Linq;
namespace Stackoverflow
{
class Program
{
static void Main()
{
var numbers = Enumerable.Range(0, 100).ToList();
var filteredNumbers = from n in numbers
where n > 50
select n;
Debugger.Break();
foreach(int f in filteredNumbers)
{
Console.WriteLine(f);
}
}
}
}
When you look at filteredNumbers on the Debugger.Break() statement you will see the following:
The Results View options has the Value: "Expanding the Results View will enumerate the IEnumerable". And that's what's happening in the Debugger.
When you look at the variable with the debugger, Visual Studio is executing the iterator. That's why you see the results.
It's for the same reason that you should not put i++ in the watch window, because the code is actually executed.
Related
If I execute ONLY the 1st part of the following short script in Robo3T, I get the results printed to the screen.
If I execute it with 2nd part, I only get the standard answer "Script executed successfully, but there are no results to show".
How can I print intermediate results such as those expected for 2nd part ?
I precise that concession & mission are both similar JSON objects.
I spent hours on this simple question. Please help.
var mission = db.mission.find({"googleCalendarEventId":"QiVJdbL"});
while (mission.hasNext()) {
var record = mission.next();
print(record.googleCalendarEventId + "," + record.concessionIdSet[0])
};
// 2nd part //
var concession = db.cursor.findOne({"_id": ObjectId(mission.concessionIdSet[0])});
while (concession.hasNext()) {
var record = concession.next();
print(record)
};
Thanks again #stennie, for others who would have the same issues, here's one code that worked for me and the 2 errors I committed :
1/ difference between find (--> cursor) and findOne (--> 1 element)
2/ actions in the loop had to be nested inside the loop --> I used a function and it works:
const missions = db.mission.find({
$and:[{"concessionToInvoice": {$exists: false}},
{"concessionIdSet":{$size:1}}]
});
missions.forEach((mission) => {
const concession = getConcession(mission);
print(mission.googleCalendarEventId+"- invoice to :"+concession.name);
mission.concessionToInvoice = getConcessionToInvoice(concession); //another function
db.mission.save(mission);
});
function getConcession(mission){
const concession = db.concession.findOne({"_id": ObjectId(mission.concessionIdSet[0])});
return concession;
}
I have found a few articles like this one:
http://devtoolshed.com/using-stored-procedures-entity-framework-scalar-return-values
Yet when I take the step to create a function import for a int32 scalar, this is what gets generated:
public ObjectResult<Nullable<global::System.Int32>> MyStoredProcedure(Nullable<global::System.Int32> orderId)
{
ObjectParameter orderIdParameter;
if (orderId.HasValue)
{
orderIdParameter = new ObjectParameter("OrderId", orderId);
}
else
{
orderIdParameter = new ObjectParameter("OrderId", typeof(global::System.Int32));
}
return base.ExecuteFunction<Nullable<global::System.Int32>>("MyStoredProcedure", orderIdParameter);
}
I am able to call the procedure with this, but am not able to get to the underlying scalar:
ObjectResult<int?> result = myEntities.MyProcedure(orderId);
In the code examples I have seen, I should get context.MyProcedure().SingleOrDefault().
Try this:
int? result = myEntities.MyProcedure(orderId).FirstOrDefault();
I have been using CouchDB for quite sometime without any issues. That is up until now. I recently saw something in my map/reduce results which I had overlooked!
This is before performing a sum on the "avgs" variable. I'm basically trying to find the average of all values pertaining to a particular key. Nothing fancy. The result is as expected.
Note the result for timestamp 1308474660000 (4th row in the table):
Now I sum the "avgs" array. Now here is something that is peculiar about the result. The sum for the key with timestamp 1308474660000 is a null!! Why is CouchDB spitting out nulls for a simple sum? I tried with a custom addition function and its the same problem.
Can someone explain to me why is there this issue with my map/reduce result?
CouchDB version: 1.0.1
UPDATE:
After doing a rereduce I get a reduce overflow error!
Error: reduce_overflow_error
Reduce output must shrink more rapidly: Current output: '["001,1,1,1,1,1,11,1,1,1,1,1,1,11,1,1,1,1,1,1,11,1,1,1,1,1,1,11,1,1,1,1,1,101,1,1,1,1,1,1,11,1,1,1,1'... (first 100 of 396 bytes)
This is my modified reduce function:
function (key, values, rereduce) {
if(!rereduce) {
var avgs = [];
for(var i=values.length-1; i>=0 ; i--) {
avgs.push(Number(values[i][0])/Number(values[i][1]));
}
return avgs;
} else {
return sum(values);
};
}
UPDATE 2:
Well now it has gotten worse. Its selectively rereducing. Also, the ones it has rereduced show wrong results. The length of the value in 4th row for timestamp (1308474660000) should be 2 and not 3.
UPDATE 3:
I finally got it to work. I hadn't understood the specifics of rereduce properly. AFAIK, Couchdb itself decides how to/when to rereduce. In this example, whenever the array was long enough to process, Couchdb would send it to rereduce. So I basically had to sum twice. Once in reduce, and again in rereduce.
function (key, values, rereduce) {
if(!rereduce) {
var avgs = [];
for(var i=values.length-1; i>=0 ; i--) {
avgs.push(Number(values[i][0])/Number(values[i][1]));
}
return sum(avgs);
} else {
return sum(values); //If my understanding of rereduce is correct, it only receives only the avgs that are large enough to not be processed by reduce.
}
}
Your for loop in the reduce function is probably not doing what you think it is. For example, it might be throwing an exception that you did not expect.
You are expecting an array of 2-tuples:
// Expectation
values = [ [value1, total1]
, [value2, total2]
, [value3, total3]
];
During a re-reduce, the function will get old results from itself before.
// Re-reduce values
values = [ avg1
, avg2
, avg3
]
Therefore I would begin by examining how your code works if and when rereduce is true. Perhaps something simple will fix it (although often I have to log() things until I find the problem.)
function(keys, values, rereduce) {
if(rereduce)
return sum(values);
// ... then the same code as before.
}
I will elaborate on my count/sum comment, just in case you are curious.
This code is not tested, but hopefully you will get the idea. The end result is always a simple object {"count":C, "sum":S} and you know the average by computing S / C.
function (key, values, rereduce) {
// Reduce function
var count = 0;
var sum = 0;
var i;
if(!rereduce) {
// `values` stores actual map output
for(i = 0; i < values.length; i++) {
count += Number(values[i][1]);
sum += Number(values[i][0]);
}
return {"count":count, "sum":sum};
}
else {
// `values` stores count/sum objects returned previously.
for(i = 0; i < values.length; i++) {
count += values[i].count;
sum += values[i].sum;
}
return {"count":count, "sum":sum};
}
}
I use the following code to do average. Hope it helps.
function (key, values) {
return sum(values)/values.length;
}
I have an issue implementing CCR with SQL. It seems that when I step through my code the updates and inserts I am trying to execute work great. But when I run through my interface without any breakpoints, it seems to be working and it shows the inserts, updates, but at the end of the run, nothing got updated to the database.
I proceeded to add a pause to my code every time I pull anew thread from my pool and it works... but that defeats the purpose of async coding right? I want my interface to be faster, not slow it down...
Any suggestions... here is part of my code:
I use two helper classes to set my ports and get a response back...
/// <summary>
/// Gets the Reader, requires connection to be managed
/// </summary>
public static PortSet<Int32, Exception> GetReader(SqlCommand sqlCommand)
{
Port<Int32> portResponse = null;
Port<Exception> portException = null;
GetReaderResponse(sqlCommand, ref portResponse, ref portException);
return new PortSet<Int32, Exception>(portResponse, portException);
}
// Wrapper for SqlCommand's GetResponse
public static void GetReaderResponse(SqlCommand sqlCom,
ref Port<Int32> portResponse, ref Port<Exception> portException)
{
EnsurePortsExist(ref portResponse, ref portException);
sqlCom.BeginExecuteNonQuery(ApmResultToCcrResultFactory.Create(
portResponse, portException,
delegate(IAsyncResult ar) { return sqlCom.EndExecuteNonQuery(ar); }), null);
}
then I do something like this to queue up my calls...
DispatcherQueue queue = CreateDispatcher();
String[] commands = new String[2];
Int32 result = 0;
commands[0] = "exec someupdateStoredProcedure";
commands[1] = "exec someInsertStoredProcedure '" + Settings.Default.RunDate.ToString() + "'";
for (Int32 i = 0; i < commands.Length; i++)
{
using (SqlConnection connSP = new SqlConnection(Settings.Default.nbfConn + ";MultipleActiveResultSets=true;Async=true"))
using (SqlCommand cmdSP = new SqlCommand())
{
connSP.Open();
cmdSP.Connection = connSP;
cmdSP.CommandTimeout = 150;
cmdSP.CommandText = "set arithabort on; " + commands[i];
Arbiter.Activate(queue, Arbiter.Choice(ApmToCcrAdapters.GetReader(cmdSP),
delegate(Int32 reader) { result = reader; },
delegate(Exception e) { result = 0; throw new Exception(e.Message); }));
}
}
where ApmToCcrAdapters is the class name where my helper methods are...
The problem is when I pause my code right after the call to Arbiter.Activate and I check my database, everything looks fine... if I get rid of the pause ad run my code through, nothing happens to the database, and no exceptions are thrown either...
The problem here is that you are calling Arbiter.Activate in the scope of your two using blocks. Don't forget that the CCR task you create is queued and the current thread continues... right past the scope of the using blocks. You've created a race condition, because the Choice must execute before connSP and cmdSP are disposed and that's only going to happen when you're interfering with the thread timings, as you have observed when debugging.
If instead you were to deal with disposal manually in the handler delegates for the Choice, this problem would no longer occur, however this makes for brittle code where it's easy to overlook disposal.
I'd recommend implementing the CCR iterator pattern and collecting results with a MulitpleItemReceive so that you can keep your using statements. It makes for cleaner code. Off the top of my head it would look something like this:
private IEnumerator<ITask> QueryIterator(
string command,
PortSet<Int32,Exception> resultPort)
{
using (SqlConnection connSP =
new SqlConnection(Settings.Default.nbfConn
+ ";MultipleActiveResultSets=true;Async=true"))
using (SqlCommand cmdSP = new SqlCommand())
{
Int32 result = 0;
connSP.Open();
cmdSP.Connection = connSP;
cmdSP.CommandTimeout = 150;
cmdSP.CommandText = "set arithabort on; " + commands[i];
yield return Arbiter.Choice(ApmToCcrAdapters.GetReader(cmdSP),
delegate(Int32 reader) { resultPort.Post(reader); },
delegate(Exception e) { resultPort.Post(e); });
}
}
and you could use it something like this:
var resultPort=new PortSet<Int32,Exception>();
foreach(var command in commands)
{
Arbiter.Activate(queue,
Arbiter.FromIteratorHandler(()=>QueryIterator(command,resultPort))
);
}
Arbiter.Activate(queue,
Arbiter.MultipleItemReceive(
resultPort,
commands.Count(),
(results,exceptions)=>{
//everything is done and you've got 2
//collections here, results and exceptions
//to process as you want
}
)
);
Here is code of very simple expression evaluator using IronRuby
public class BasicRubyExpressionEvaluator
{
ScriptEngine engine;
ScriptScope scope;
public Exception LastException
{
get; set;
}
private static readonly Dictionary<string, ScriptSource> parserCache = new Dictionary<string, ScriptSource>();
public BasicRubyExpressionEvaluator()
{
engine = Ruby.CreateEngine();
scope = engine.CreateScope();
}
public object Evaluate(string expression, DataRow context)
{
ScriptSource source;
parserCache.TryGetValue(expression, out source);
if (source == null)
{
source = engine.CreateScriptSourceFromString(expression, SourceCodeKind.SingleStatement);
parserCache.Add(expression, source);
}
var result = source.Execute(scope);
return result;
}
public void SetVariable(string variableName, object value)
{
scope.SetVariable(variableName, value);
}
}
and here is problem.
var evaluator = new BasicRubyExpressionEvaluator();
evaluator.SetVariable("a", 10);
evaluator.SetVariable("b", 1 );
evaluator.Evaluate("a+b+2", null);
vs
var evaluator = new BasicRubyExpressionEvaluator();
evaluator.Evaluate("10+1+2", null);
First Is 25 times slower than second. Any suggestions? String.Replace is not a solution for me.
I do not think the performance you are seeing is due to variable setting; the first execution of IronRuby in a program is always going to be slower than the second, regardless of what you're doing, since most of the compiler isn't loaded in until code is actually run (for startup performance reasons). Please try that example again, maybe running each version of your code in a loop, and you'll see the performance is roughly equivalent; the variable-version does have some overhead of method-dispatch to get the variables, but that should be negligible if you run it enough.
Also, in your hosting code, how come you are holding onto ScriptScopes in a dictionary? I would hold onto CompiledCode (result of engine.CreateScriptSourceFromString(...).Compile()) instead -- as that will help a lot more in repeat runs.
you can of course first build the string something like
evaluator.Evaluate(string.format("a={0}; b={1}; a + b + 2", 10, 1))
Or you can make it a method
if instead of your script you return a method then you should be able to use it like a regular C# Func object.
var script = #"
def self.addition(a, b)
a + b + 2
end
"
engine.ExecuteScript(script);
var = func = scope.GetVariable<Func<object,object,object>>("addition");
func(10,1)
This is probably not a working snippet but it shows the general idea.