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  • How can I skip some block content while reading in Perl.

    - by Nano HE
    Hello. I plan to skip the block content which include the start line of "MaterializeU4()" with the subroutin() read_block below. But failed. # Read a constant definition block from a file handle. # void return when there is no data left in the file. # Otherwise return an array ref containing lines to in the block. sub read_block { my $fh = shift; my @lines; my $block_started = 0; while( my $line = <$fh> ) { # how to correct my code below? I don't need the 2nd block content. $block_started++ if ( ($line =~ /^(status)/) && (index($line, "MaterializeU4") != 0) ) ; if( $block_started ) { last if $line =~ /^\s*$/; push @lines, $line; } } return \@lines if @lines; return; } Data as below: __DATA__ status DynTest = <dynamic 100> vid = 10002 name = "DynTest" units = "" status VIDNAME9000 = <U4 MaterializeU4()> vid = 9000 name = "VIDNAME9000" units = "degC" status DynTest = <U1 100> vid = 100 name = "Hello" units = "" Output: <StatusVariables> <SVID logicalName="DynTest" type="L" value="100" vid="10002" name="DynTest" units=""></SVID> <SVID logicalName="VIDNAME9000" type="L" value="MaterializeU4()" vid="9000" name="VIDNAME9000" units="degC"></SVID> <SVID logicalName="DynTest" type="L" value="100" vid="100" name="Hello" units=""></SVID> </StatusVariables> [Updated] I print the value of index($line, "MaterializeU4"), it output 25. Then I updated the code as below $block_started++ if ( ($line =~ /^(status)/) && (index($line, "MaterializeU4") != 25) Now it works. Any comments are welcome about my practice. Thank you.

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  • How can I ignore the block content reading in Perl.

    - by Nano HE
    Hello. I plan to ignore the block content which include the start line of "MaterializeU4()" with the subroutin() read_block below. But failed. # Read a constant definition block from a file handle. # void return when there is no data left in the file. # Otherwise return an array ref containing lines to in the block. sub read_block { my $fh = shift; my @lines; my $block_started = 0; while( my $line = <$fh> ) { # how to correct my code below? I don't need the 2nd block content. $block_started++ if ( ($line =~ /^(status)/) && (index($line, "MaterializeU4") != 0) ) ; if( $block_started ) { last if $line =~ /^\s*$/; push @lines, $line; } } return \@lines if @lines; return; } Data as below: __DATA__ status DynTest = <dynamic 100> vid = 10002 name = "DynTest" units = "" status VIDNAME9000 = <U4 MaterializeU4()> vid = 9000 name = "VIDNAME9000" units = "degC" status DynTest = <U1 100> vid = 100 name = "Hello" units = "" Output: <StatusVariables> <SVID logicalName="DynTest" type="L" value="100" vid="10002" name="DynTest" units=""></SVID> <SVID logicalName="VIDNAME9000" type="L" value="MaterializeU4()" vid="9000" name="VIDNAME9000" units="degC"></SVID> <SVID logicalName="DynTest" type="L" value="100" vid="100" name="Hello" units=""></SVID> </StatusVariables> [Updated] I print the value of index($line, "MaterializeU4"), it output 25. Then I updated the code as below $block_started++ if ( ($line =~ /^(status)/) && (index($line, "MaterializeU4") != 25) Now it works. Any comments are welcome about my practice. Thank you.

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  • Rounding issue when adding floats in python, is this normal?

    - by thepearson
    I just wanted to know if this behavior is expected. If so, can someone explain to me why. This has probably been answered elsewhere I can't seem to find it using Google. Probably not searching with the right terms. I am running Ubuntu 10.04. Python 2.6.5 (r265:79063, Apr 16 2010, 13:09:56) [GCC 4.4.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> var = 10.0 >>> var 10.0 >>> var + 5 15.0 >>> var + 5.1 15.1 >>> var + 5.2 15.199999999999999 >>>

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  • Sed substitution not doing what I want and think it should do

    - by nategoose
    I have am trying to use sed to get some info that is encoded within the path of a file which is passed as a parameter to my script (Bourne sh, if it matters). From this example path, I'd like the result to be 8 PATH=/foo/bar/baz/1-1.8/sing/song I first got the regex close by using sed as grep: echo $PATH | sed -n -e "/^.*\/1-1\.\([0-9][0-9]*\).*/p" This properly recognized the string, so I edited it to make a substitution out of it: echo $PATH | sed -n -e "s/^.*\/1-1\.\([0-9][0-9]*\).*/\1/" But this doesn't produce any output. I know I'm just not seeing something simple, but would really appreciate any ideas about what I'm doing wrong or about other ways to debug sed regular expressions.

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  • Python `if x is not None` or `if not x is None`?

    - by orokusaki
    I've always thought of the if not x is None version to be more clear, but Google's style guide implies (based on this excerpt) that they use if x is not None. Is there any minor performance difference (I'm assuming not), and is there any case where one really doesn't fit (making the other a clear winner for my convention)?* *I'm referring to any singleton, rather than just None. ...to compare singletons like None. Use is or is not.

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  • Optimize INSERT / UPDATE / DELETE operation

    - by clime
    I wonder if the following script can be optimized somehow. It does write a lot to disk because it deletes possibly up-to-date rows and reinserts them. I was thinking about applying something like "insert ... on duplicate key update" and found some possibilities for single-row updates but I don't know how to apply it in the context of INSERT INTO ... SELECT query. CREATE OR REPLACE FUNCTION update_member_search_index() RETURNS VOID AS $$ DECLARE member_content_type_id INTEGER; BEGIN member_content_type_id := (SELECT id FROM django_content_type WHERE app_label='web' AND model='member'); DELETE FROM watson_searchentry WHERE content_type_id = member_content_type_id; INSERT INTO watson_searchentry (engine_slug, content_type_id, object_id, object_id_int, title, description, content, url, meta_encoded) SELECT 'default', member_content_type_id, web_member.id, web_member.id, web_member.name, '', web_user.email||' '||web_member.normalized_name||' '||web_country.name, '', '{}' FROM web_member INNER JOIN web_user ON (web_member.user_id = web_user.id) INNER JOIN web_country ON (web_member.country_id = web_country.id) WHERE web_user.is_active=TRUE; END; $$ LANGUAGE plpgsql; EDIT: Schemas of web_member, watson_searchentry, web_user, web_country: http://pastebin.com/3tRVPPVi. (content_type_id, object_id_int) in watson_searchentry is unique pair in the table but atm the index is not present (there is no use for it). This script should be run at most once a day for full rebuilds of search index.

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  • What is the role of `while`-loops in computation expressions in F#?

    - by MizardX
    If you define a While method of the builder-object, you can use while-loops in your computation expressions. The signature of the While method is: member b.While (predicate:unit->bool, body:M<'a>) : M<'a> For comparison, the signature of the For method is: member b.For (items:seq<'a>, body:unit->M<'a>) : M<'a> You should notice that, in the While-method, the body is a simple type, and not a function as in the For method. You can embed some other statements, like let and function-calls inside your computation-expressions, but those can impossibly execute in a while-loop more than once. builder { while foo() do printfn "step" yield bar() } Why is the while-loop not executed more than once, but merely repeated? Why the significant difference from for-loops? Better yet, is there some intended strategy for using while-loops in computation-expressions?

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  • Adding LambaExpression to an instance of IQueryable

    - by Paul Knopf
    ParameterExpression parameter = Expression.Parameter(typeof(Product), "x"); MemberExpression Left = Expression.MakeMemberAccess(parameter, typeof(Product).GetProperty("Name")); ConstantExpression Right = Expression.Constant(value, typeof(String)); BinaryExpression expression = Expression.Equal(Left, Right); LambdaExpression lambada = Expression.Lambda<Func<Product, bool>>(expression, parameter); Now how do I add this lambada to an instance of an IQuerybale, lets say _query _query.Where(lambada.Compile());?

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  • Can you use back references in the pattern part of a regular expression?

    - by Camsoft
    I there a way to back reference in the regular expression pattern? Example input string: Here is "quoted text" some quoted text. Say I want to pull out the quoted text, I could create the following expression: "([^"]+)" This regular expression would match quoted text. Say I want it to also support single quotes, I could change the expression to: ["']([^"']+)["'] But what if the input string has a mixture of quotes say Here is 'quoted text" some quoted text. I would not want the regex to match. Currently the regex in the second example would still match. What I would like to be able to do is if the first quote is a double quote then the closing quote must be a double. And if the start quote is single quote then the closing quote must be single. Can I use a back reference to achieve this?

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  • How do I tell if an action is a lambda expression?

    - by Keith
    I am using the EventAgregator pattern to subscribe and publish events. If a user subscribes to the event using a lambda expression, they must use a strong reference, not a weak reference, otherwise the expression can be garbage collected before the publish will execute. I wanted to add a simple check in the DelegateReference so that if a programmer passes in a lambda expression and is using a weak reference, that I throw an argument exception. This is to help "police" the code. Example: eventAggregator.GetEvent<RuleScheduler.JobExecutedEvent>().Subscribe ( e => resetEvent.Set(), ThreadOption.PublisherThread, false, // filter event, only interested in the job that this object started e => e.Value1.JobDetail.Name == jobName ); public DelegateReference(Delegate @delegate, bool keepReferenceAlive) { if (@delegate == null) throw new ArgumentNullException("delegate"); if (keepReferenceAlive) { this._delegate = @delegate; } else { //TODO: throw exception if target is a lambda expression _weakReference = new WeakReference(@delegate.Target); _method = @delegate.Method; _delegateType = @delegate.GetType(); } } any ideas? I thought I could check for @delegate.Method.IsStatic but I don't believe that works... (is every lambda expression a static?)

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  • What is corresponding Cron expression to fire in every X seconds, where X > 60?

    - by giolekva
    I want my jobs to execute in every X seconds, there's one to one matching between job and X. Also during runtime there can be registered new jobs with their own intervals. I've tried to write cron expression for such scenarios, but in documentation there's written that value of seconds can't be more than 69. So cron expression like this: "0/63 * * * * ?" isn't valid. At first sight solution of that problem seemed to be expression like this: "0/3 0/1 * * * ?", but it means completely different thing: trigger job in every three second of every minute. Can you suggest what is the right solution (cron expression) for that? I know I could use just simple timers, but I've to use cron jobs using Quartz.

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  • Building 'flat' rather than 'tree' LINQ expressions

    - by Ian Gregory
    I'm using some code (available here on MSDN) to dynamically build LINQ expressions containing multiple OR 'clauses'. The relevant code is var equals = values.Select(value => (Expression)Expression.Equal(valueSelector.Body, Expression.Constant(value, typeof(TValue)))); var body = equals.Aggregate<Expression>((accumulate, equal) => Expression.Or(accumulate, equal)); This generates a LINQ expression that looks something like this: (((((ID = 5) OR (ID = 4)) OR (ID = 3)) OR (ID = 2)) OR (ID = 1)) I'm hitting the recursion limit (100) when using this expression, so I'd like to generate an expression that looks like this: (ID = 5) OR (ID = 4) OR (ID = 3) OR (ID = 2) OR (ID = 1) How would I modify the expression building code to do this?

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  • How to construct LambdaExpression with conversion

    - by nerijus
    I need to sort in ajax response grid by column name. Column value is number stored as a string. Let's say some trivial class (in real-life situation there is no possibility to modify this class): class TestObject { public TestObject(string v) { this.Value = v; } public string Value { get; set; } } then simple test: [Test] public void LambdaConstructionTest() { var queryable = new List<TestObject> { new TestObject("5"), new TestObject("55"), new TestObject("90"), new TestObject("9"), new TestObject("09"), new TestObject("900"), }.AsQueryable(); var sortingColumn = "Value"; ParameterExpression parameter = Expression.Parameter(queryable.ElementType); MemberExpression property = Expression.Property(parameter, sortingColumn); //// tried this one: var c = Expression.Convert(property, typeof(double)); LambdaExpression lambda = Expression.Lambda(property, parameter); //// constructs: o=>o.Value var callExpression = Expression.Call(typeof (Double), "Parse", null, property); var methodCallExpression = Expression.Call( typeof(Queryable), "OrderBy", new[] { queryable.ElementType, property.Type }, queryable.Expression, Expression.Quote(lambda)); // works, but sorts by string values. //Expression.Quote(callExpression)); // getting: System.ArgumentException {"Quoted expression must be a lambda"} var querable = queryable.Provider.CreateQuery<TestObject>(methodCallExpression); // return querable; // <- this is the return of what I need. } Sorry for not being clear in my first post as @SLaks answer was correct but I do not know how to construct correct lambda expression in this case.

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  • How can I make this work with deep properties

    - by Martin Robins
    Given the following code... class Program { static void Main(string[] args) { Foo foo = new Foo { Bar = new Bar { Name = "Martin" }, Name = "Martin" }; DoLambdaStuff(foo, f => f.Name); DoLambdaStuff(foo, f => f.Bar.Name); } static void DoLambdaStuff<TObject, TValue>(TObject obj, Expression<Func<TObject, TValue>> expression) { // Set up and test "getter"... Func<TObject, TValue> getValue = expression.Compile(); TValue stuff = getValue(obj); // Set up and test "setter"... ParameterExpression objectParameterExpression = Expression.Parameter(typeof(TObject)), valueParameterExpression = Expression.Parameter(typeof(TValue)); Expression<Action<TObject, TValue>> setValueExpression = Expression.Lambda<Action<TObject, TValue>>( Expression.Block( Expression.Assign(Expression.Property(objectParameterExpression, ((MemberExpression)expression.Body).Member.Name), valueParameterExpression) ), objectParameterExpression, valueParameterExpression ); Action<TObject, TValue> setValue = setValueExpression.Compile(); setValue(obj, stuff); } } class Foo { public Bar Bar { get; set; } public string Name { get; set; } } class Bar { public string Name { get; set; } } The call to DoLambdaStuff(foo, f => f.Name) works ok because I am accessing a shallow property, however the call to DoLambdaStuff(foo, f => f.Bar.Name) fails - although the creation of the getValue function works fine, the creation of the setValueExpression fails because I am attempting to access a deep property of the object. Can anybody please help me to modify this so that I can create the setValueExpression for deep properties as well as shallow? Thanks.

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  • Faster quadrature decoder loops with Python code

    - by Kelei
    I'm working with a BeagleBone Black and using Adafruit's IO Python library. Wrote a simple quadrature decoding function and it works perfectly fine when the motor runs at about 1800 RPM. But when the motor runs at higher speeds, the code starts missing some of the interrupts and the encoder counts start to accumulate errors. Do you guys have any suggestions as to how I can make the code more efficient or if there are functions which can cycle the interrupts at a higher frequency. Thanks, Kel Here's the code: # Define encoder count function def encodercount(term): global counts global Encoder_A global Encoder_A_old global Encoder_B global Encoder_B_old global error Encoder_A = GPIO.input('P8_7') # stores the value of the encoders at time of interrupt Encoder_B = GPIO.input('P8_8') if Encoder_A == Encoder_A_old and Encoder_B == Encoder_B_old: # this will be an error error += 1 print 'Error count is %s' %error elif (Encoder_A == 1 and Encoder_B_old == 0) or (Encoder_A == 0 and Encoder_B_old == 1): # this will be clockwise rotation counts += 1 print 'Encoder count is %s' %counts print 'AB is %s %s' % (Encoder_A, Encoder_B) elif (Encoder_A == 1 and Encoder_B_old == 1) or (Encoder_A == 0 and Encoder_B_old == 0): # this will be counter-clockwise rotation counts -= 1 print 'Encoder count is %s' %counts print 'AB is %s %s' % (Encoder_A, Encoder_B) else: #this will be an error as well error += 1 print 'Error count is %s' %error Encoder_A_old = Encoder_A # store the current encoder values as old values to be used as comparison in the next loop Encoder_B_old = Encoder_B # Initialize the interrupts - these trigger on the both the rising and falling GPIO.add_event_detect('P8_7', GPIO.BOTH, callback = encodercount) # Encoder A GPIO.add_event_detect('P8_8', GPIO.BOTH, callback = encodercount) # Encoder B # This is the part of the code which runs normally in the background while True: time.sleep(1)

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  • GridView ObjectDataSource LINQ Paging and Sorting using multiple table query.

    - by user367426
    I am trying to create a pageing and sorting object data source that before execution returns all results, then sorts on these results before filtering and then using the take and skip methods with the aim of retrieving just a subset of results from the database (saving on database traffic). this is based on the following article: http://www.singingeels.com/Blogs/Nullable/2008/03/26/Dynamic_LINQ_OrderBy_using_String_Names.aspx Now I have managed to get this working even creating lambda expressions to reflect the sort expression returned from the grid even finding out the data type to sort for DateTime and Decimal. public static string GetReturnType<TInput>(string value) { var param = Expression.Parameter(typeof(TInput), "o"); Expression a = Expression.Property(param, "DisplayPriceType"); Expression b = Expression.Property(a, "Name"); Expression converted = Expression.Convert(Expression.Property(param, value), typeof(object)); Expression<Func<TInput, object>> mySortExpression = Expression.Lambda<Func<TInput, object>>(converted, param); UnaryExpression member = (UnaryExpression)mySortExpression.Body; return member.Operand.Type.FullName; } Now the problem I have is that many of the Queries return joined tables and I would like to sort on fields from the other tables. So when executing a query you can create a function that will assign the properties from other tables to properties created in the partial class. public static Account InitAccount(Account account) { account.CurrencyName = account.Currency.Name; account.PriceTypeName = account.DisplayPriceType.Name; return account; } So my question is, is there a way to assign the value from the joined table to the property of the current table partial class? i have tried using. from a in dc.Accounts where a.CompanyID == companyID && a.Archived == null select new { PriceTypeName = a.DisplayPriceType.Name}) but this seems to mess up my SortExpression. Any help on this would be much appreciated, I do understand that this is complex stuff.

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  • How can I edit (in MS Expression Web ) FrontPage Site Parameters (Substitutions)?

    - by Clay Nichols
    Or, asked another way: Where are the values for MS Front Page Substitions (Site Parameters) stored? (so that I can edit in Web Expressions) Background I'm ashamed to admit that I've been maintaining our company's website in MS FrontPage for over 9 years. I'm moving it to Expression Web, which will display the Substitutions (stored as Site Parameters) but I can't figure out where to edit them. I tried searching the source folders for the website (on my development PC) for the name of the parameter (s-Variable=hoursOfOperation) but did not find it (other than in the files it was actually used in.

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  • How can I improve the workflow between developer and designer with Expression Blend?

    - by Amenti
    We use WPF and Expression Blend 4. I'm trying to improve our workflow by tutoring one of our designers to use it for styling and animation. Slowly but surely I get the impression Blend in itself is to technical for the designer in question. I myself use it only occasionally (it's great for Visual States for instance) because a lot of things are easier done in code or not possible at all in Blend alone. It seems a developer with design experience is a lot more productive with it than a sole designer. Are there any good resources or advice as to how I can improve this workflow?

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  • How to improve workflow between developer and designer with Expression Blend?

    - by Amenti
    We use WPF and Expression Blend 4. I'm trying to improve our workflow by tutoring one of our designers to use it for styling and animation. Slowly but surely I get the impression Blend in itself is to technical for the designer in question. I myself use it only occasionally (it's great for Visual States for instance) because a lot of things are easier done in code or not possible at all in Blend alone. It seems a developer with design experience is a lot more productive with it than a sole designer. Are there any good online resources or advice you could give me how to improve this situation?

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  • Access 2007: How can I make this EXPRESSION less complex?

    - by Mike
    Access is telling me that my new expression is to complex. It used to work when we had 10 service levels, but now we have 19! Great! My expression is checking the COST of our services in the [PriceCharged] field and then assigning the appropriate HOURS [Servicelevel] when I perform a calculation to work out how much REVENUE each colleague has made when working for a client. The [EstimatedTime] field stores the actual hours each colleague has worked. [EstimatedTime]/[ServiceLevel]*[PriceCharged] Great. Below is the breakdown of my COST to HOURS expression. I've put them on different lines to make it easier to read - please do not be put off by the length of this post, it's all the same info in the end. Many thanks,Mike ServiceLevel: IIf([pricecharged]=100(COST),6(HOURS), IIf([pricecharged]=200 Or [pricecharged]=210,12.5, IIf([pricecharged]=300,19, IIf([pricecharged]=400 Or [pricecharged]=410,25, IIf([pricecharged]=500,31, IIf([pricecharged]=600,37.5, IIf([pricecharged]=700,43, IIf([pricecharged]=800 Or [pricecharged]=810,50, IIf([pricecharged]=900,56, IIf([pricecharged]=1000,62.5, IIf([pricecharged]=1100,69, IIf([pricecharged]=1200 Or [pricecharged]=1210,75, IIf([pricecharged]=1300 Or [pricecharged]=1310,100, IIf([pricecharged]=1400,125, IIf([pricecharged]=1500,150, IIf([pricecharged]=1600,175, IIf([pricecharged]=1700,200, IIf([pricecharged]=1800,225, IIf([pricecharged]=1900,250,0)))))))))))))))))))

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  • Knockout with ASP.Net MVC2 - HTML Extension Helpers for input controls

    - by Renso
    Goal: Defining Knockout-style input controls can be tedious and also may be something that you may find obtrusive, mixing your HTML with data bind syntax as well as binding your aspx, ascx files to Knockout. The goal is to make specifying Knockout specific HTML tags easy, seamless really, as well as being able to remove references to Knockout easily. Environment considerations: ASP.Net MVC2 or later Knockoutjs.js How to:     public static class HtmlExtensions     {         public static string DataBoundCheckBox(this HtmlHelper helper, string name, bool isChecked, object htmlAttributes)         {             var builder = new TagBuilder("input");             var dic = new RouteValueDictionary(htmlAttributes) { { "data-bind", String.Format("checked: {0}", name) } };             builder.MergeAttributes(dic);             builder.MergeAttribute("type", @"checkbox");             builder.MergeAttribute("name", name);             builder.MergeAttribute("value", @"true");             if (isChecked)             {                 builder.MergeAttribute("checked", @"checked");             }             return builder.ToString(TagRenderMode.SelfClosing);         }         public static MvcHtmlString DataBoundSelectList(this HtmlHelper helper, string name, IEnumerable<SelectListItem> selectList, String optionLabel)         {             var attrProperties = new StringBuilder();             attrProperties.Append(String.Format("optionsText: '{0}'", name));             if (!String.IsNullOrEmpty(optionLabel)) attrProperties.Append(String.Format(", optionsCaption: '{0}'", optionLabel));             attrProperties.Append(String.Format(", value: {0}", name));             var dic = new RouteValueDictionary { { "data-bind", attrProperties.ToString() } };             return helper.DropDownList(name, selectList, optionLabel, dic);         }         public static MvcHtmlString DataBoundSelectList(this HtmlHelper helper, string name, IEnumerable<SelectListItem> selectList, String optionLabel, object htmlAttributes)         {             var attrProperties = new StringBuilder();             attrProperties.Append(String.Format("optionsText: '{0}'", name));             if (!String.IsNullOrEmpty(optionLabel)) attrProperties.Append(String.Format(", optionsCaption: '{0}'", optionLabel));             attrProperties.Append(String.Format(", value: {0}", name));             var dic = new RouteValueDictionary(htmlAttributes) {{"data-bind", attrProperties}};             return helper.DropDownList(name, selectList, optionLabel, dic);         }         public static String DataBoundSelectList(this HtmlHelper helper, String options, String optionsText, String value)         {             return String.Format("<select data-bind=\"options: {0},optionsText: '{1}',value: {2}\"></select>", options, optionsText, value);         }         public static MvcHtmlString DataBoundTextBox(this HtmlHelper helper, string name, object value, object htmlAttributes)         {             var dic = new RouteValueDictionary(htmlAttributes);             dic.Add("data-bind", String.Format("value: {0}", name));             return helper.TextBox(name, value, dic);         }         public static MvcHtmlString DataBoundTextBox(this HtmlHelper helper, string name, string observable, object value, object htmlAttributes)         {             var dic = new RouteValueDictionary(htmlAttributes);             dic.Add("data-bind", String.Format("value: {0}", observable));             return helper.TextBox(name, value, dic);         }         public static MvcHtmlString DataBoundTextArea(this HtmlHelper helper, string name, string value, int rows, int columns, object htmlAttributes)         {             var dic = new RouteValueDictionary(htmlAttributes);             dic.Add("data-bind", String.Format("value: {0}", name));             return helper.TextArea(name, value, rows, columns, dic);         }         public static MvcHtmlString DataBoundTextArea(this HtmlHelper helper, string name, string observable, string value, int rows, int columns, object htmlAttributes)         {             var dic = new RouteValueDictionary(htmlAttributes);             dic.Add("data-bind", String.Format("value: {0}", observable));             return helper.TextArea(name, value, rows, columns, dic);         }         public static string BuildUrlFromExpression<T>(this HtmlHelper helper, Expression<Action<T>> action)         {             var values = CreateRouteValuesFromExpression(action);             var virtualPath = helper.RouteCollection.GetVirtualPath(helper.ViewContext.RequestContext, values);             if (virtualPath != null)             {                 return virtualPath.VirtualPath;             }             return null;         }         public static string ActionLink<T>(this HtmlHelper helper, Expression<Action<T>> action, string linkText)         {             return helper.ActionLink(action, linkText, null);         }         public static string ActionLink<T>(this HtmlHelper helper, Expression<Action<T>> action, string linkText, object htmlAttributes)         {             var values = CreateRouteValuesFromExpression(action);             var controllerName = (string)values["controller"];             var actionName = (string)values["action"];             values.Remove("controller");             values.Remove("action");             return helper.ActionLink(linkText, actionName, controllerName, values, new RouteValueDictionary(htmlAttributes)).ToHtmlString();         }         public static MvcForm Form<T>(this HtmlHelper helper, Expression<Action<T>> action)         {             return helper.Form(action, FormMethod.Post);         }         public static MvcForm Form<T>(this HtmlHelper helper, Expression<Action<T>> action, FormMethod method)         {             var values = CreateRouteValuesFromExpression(action);             string controllerName = (string)values["controller"];             string actionName = (string)values["action"];             values.Remove("controller");             values.Remove("action");             return helper.BeginForm(actionName, controllerName, values, method);         }         public static MvcForm Form<T>(this HtmlHelper helper, Expression<Action<T>> action, FormMethod method, object htmlAttributes)         {             var values = CreateRouteValuesFromExpression(action);             string controllerName = (string)values["controller"];             string actionName = (string)values["action"];             values.Remove("controller");             values.Remove("action");             return helper.BeginForm(actionName, controllerName, values, method, new RouteValueDictionary(htmlAttributes));         }         public static string VertCheckBox(this HtmlHelper helper, string name, bool isChecked)         {             return helper.CustomCheckBox(name, isChecked, null);         }          public static string CustomCheckBox(this HtmlHelper helper, string name, bool isChecked, object htmlAttributes)         {             TagBuilder builder = new TagBuilder("input");             builder.MergeAttributes(new RouteValueDictionary(htmlAttributes));             builder.MergeAttribute("type", "checkbox");             builder.MergeAttribute("name", name);             builder.MergeAttribute("value", "true");             if (isChecked)             {                 builder.MergeAttribute("checked", "checked");             }             return builder.ToString(TagRenderMode.SelfClosing);         }         public static string Script(this HtmlHelper helper, string script, object scriptAttributes)         {             var pathForCRMScripts = ScriptsController.GetPathForCRMScripts();             if (ScriptOptimizerConfig.EnableMinimizedFileLoad)             {                 string newPathForCRM = pathForCRMScripts + "Min/";                 ScriptsController.ServerPathMapper = new ServerPathMapper();                 string fullPath = ScriptsController.ServerMapPath(newPathForCRM);                 if (!File.Exists(fullPath + script))                     return null;                 if (!Directory.Exists(fullPath))                     return null;                 pathForCRMScripts = newPathForCRM;             }             var builder = new TagBuilder("script");             builder.MergeAttributes(new RouteValueDictionary(scriptAttributes));             builder.MergeAttribute("type", @"text/javascript");             builder.MergeAttribute("src", String.Format("{0}{1}", pathForCRMScripts.Replace("~", String.Empty), script));             return builder.ToString(TagRenderMode.SelfClosing);         }         private static RouteValueDictionary CreateRouteValuesFromExpression<T>(Expression<Action<T>> action)         {             if (action == null)                 throw new InvalidOperationException("Action must be provided");             var body = action.Body as MethodCallExpression;             if (body == null)             {                 throw new InvalidOperationException("Expression must be a method call");             }             if (body.Object != action.Parameters[0])             {                 throw new InvalidOperationException("Method call must target lambda argument");             }             // This will build up a RouteValueDictionary containing the controller name, action name, and any             // parameters passed as part of the "action" parameter.             string name = body.Method.Name;             string controllerName = typeof(T).Name;             if (controllerName.EndsWith("Controller", StringComparison.OrdinalIgnoreCase))             {                 controllerName = controllerName.Remove(controllerName.Length - 10, 10);             }             var values = BuildParameterValuesFromExpression(body) ?? new RouteValueDictionary();             values.Add("controller", controllerName);             values.Add("action", name);             return values;         }         private static RouteValueDictionary BuildParameterValuesFromExpression(MethodCallExpression call)         {             // Build up a RouteValueDictionary containing parameter names as keys and parameter values             // as values based on the MethodCallExpression passed in.             var values = new RouteValueDictionary();             ParameterInfo[] parameters = call.Method.GetParameters();             // If the passed in method has no parameters, just return an empty dictionary.             if (parameters.Length == 0)             {                 return values;             }             for (int i = 0; i < parameters.Length; i++)             {                 object parameterValue;                 Expression expression = call.Arguments[i];                 // If the current parameter is a constant, just use its value as the parameter value.                 var constant = expression as ConstantExpression;                 if (constant != null)                 {                     parameterValue = constant.Value;                 }                 else                 {                     // Otherwise, compile and execute the expression and use that as the parameter value.                     var function = Expression.Lambda<Func<object>>(Expression.Convert(expression, typeof(object)),                                                                    new ParameterExpression[0]);                     try                     {                         parameterValue = function.Compile()();                     }                     catch                     {                         parameterValue = null;                     }                 }                 values.Add(parameters[i].Name, parameterValue);             }             return values;         }     }   Some observations: The first two DataBoundSelectList overloaded methods are specifically built to load the data right into the drop down box as part of the HTML response stream rather than let Knockout's engine populate the options client-side. The third overloaded method does it client-side via the viewmodel. The first two overloads can be done when you have no requirement to add complex JSON objects to your lists. Furthermore, why render and parse the JSON object when you can have it all built and rendered server-side like any other list control.

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