.net - Translate This Code Into An Expression Tree?
Feb 12, 2010
I have a hashing method whose operations depend on input to the function. Profiling the program has shown that too much time is spent evaluating this hash method. I want to try changing it into an expression tree, so the inner loop checks can be done once.
Here is a simplified version of the function (I undid some obvious optimizations for the example, and took out any input validation):
Private Function Checksum(ByVal inputValues As IEnumerable(Of UInt32),
ByVal declarations As IEnumerable(Of String),
ByVal statements As IEnumerable(Of String)) As UInt32
Dim variables = New Dictionary(Of Char, UInt32)
[code]....
I want to create a function which takes the declarations and statements and outputs a specialized expression tree representing a function which takes an IEnumerable of UInt32 and returns a UInt32.Follow-Up:I succeeded, and the speed-up was ridiculous (an order of magnitude). The main things I had to learn where:Use Expression.Lambda and Expression.Compile to get a delegate you can actually use.The Expression.Block factory method has a 'variables' parameter you (essentially) use to declare locals.Expression.lambda has 'parameters'.If you call Expression.Parameter twice, you're dealing with two different variables (even if their name is the same)! Store the result for later usage. Same for labels, etc.The result of a BlockExpression is the last expression in the block.
The following LINQ query resp. call of the extension method Select in Visual Basic 2010 is working fine:
Dim qAvSalary = qJobData.Select(Function(e) e.AvSalary) But doing so I am not able to specify the name of property I want the query (e.g. AvSalary) using a string variable. This should be possible if I use a LINQ expression tree. Searching and trying a long time on how to translate the query to a corresponding expression tree was not successful. My final approach is:
1) I am begginner to dynamic Linq and having serious trouble creating expression tree after WHERE
say.: items.Category_ID=4
I tried to construct it like: Dim products = From items In mydatacontent.Products
Dim AA As ParameterExpression = Expression.Parameter(GetType(String), "items")
Dim left1 As Expression = Expression.Property(AA, GetType(String).GetProperty("Category_ID")) here is the error Dim right1 As Expression = Expression.Constant("4") Dim BB As Expression = Expression.Equal(left1, right1)
Im getting some VB.Net Late binding operations cannot be converted to an expression tree. errors, have search here on the site and can only find solutions to the SQL get data code, not to my problem. The error "Late binding operations cannot be converted to an expression tree." At all my x.NAME) lines !? Im new to this so can anyone say me why i get this error..
I currently have a View in MVC where I pass a single set of data to the view. However, I've come across a problem where I am having to use a LINQ query within a For Each loop in the View to pull out additional information from a SQL View of data from another DB.
The error I'm getting is Late binding operations cannot be converted to an expression tree.
The particular snippet I'm encountering the error on is:
What I am about to do build is a UI that will allow a power user to build complex queries.
This is non-trivial, but very common. So before I re-invent the wheel, I would like to see if anybody can point me to some already-written free code or release some of their own.
Required:
To be able to specify some 'where-clause' type logic like this: Age>21 and (Citizen=True or HasGreeCard=True) but without having to type the query code, instead, use a UI with constrained options and on-the-fly syntax checking (e.g., no unclosed parenthesis or ending a term with an Operator).
I've seen this type of thing in many line-of-business apps, where you can say 'add condition' and another line appears on the UI like this:
Dropdown of fields Dropdown of ops (=, >, etc) Blank box for entry
And you can add more lines, and the lines are all and'ed, but you can also decide to OR a few, or insert parenthesis (explicity or via indenting), NOT a line, insert, delete, and move lines around, etc.
Not required but nice:
WPF - I could convert from winforms. Extensibility using OO constructs. Validate the sanity of the query. Emit a System.Linq.Expressions expression tree - or similar data structure. If it attempts to execute the query I don't need that; but I don't mind removing it.
I have built a database structure that represents a category tree to help classify some of the data we have stored. The implementation is that each record in the Category table has a nullable foreign key back into the Category table to represent the parent Category of this category (one-to-many), essentially allowing for subcategories within a broader parent level. There is a CategoryMembership table that links a record in the Item table to its respective Category (many-to-many). I have created the DBML for this database, and it has a member access structure that includes the following:
While looking in the dataset designer for a database table I am doing in visual basic 2008 I found a line for expressions under the property menu for a specific column. I need to know the code that I would put in this expression line so that this column adds up the numbers I input into three other columns and displays that number in the column. I need it to automatically calculate this for each row in the database table.
I have found the following code which can get the harddisk no in VB6.0.I would like to translate it into vb.net code.I have tried the auto upgrade function in vb2005 and translated the following code to vb.net, but the outcome did not run probably.Can anyone give me some help to translate the following VB6.0 code into vb.net code?
I need to translate line 4 in the code snippet below into VB. For some reason I cannot get this done tonight. I am either too tired or having a brain drain.[code]
I have a line of C# code and can't translate it correctly. 'myString' is a string and 'a' and 'k' are both UInt:a += (uint)(myString[k + 0] + (myString[k + 1] << 8) + (myString[k + 2] << 16) + (myString[k + 3] << 24)); Translators for VB suggest the following but I get "Operator '<<' is not defined for types 'Char' and 'Integer': a += CUInt(myString(k + 0) + (myString(k + 1) << 8) + (myString(k + 2) << 16) + (myString(k + 3) << 24))
I have this working on VB6 that saves a query in a excel sheet:
[Code]...
The XLSNombre is a variable with the name of the excel file that has been set before. The connection I have in .NET is to SQL server (but is the same). How can I use this code (or..how can I make this code work for .NET) or what is the equivalent of this for .NET? I found some solutions but with inserts of single rows or I have to set the title of the columns, I dont find any "simple" solution to do an "insert into" (like the code I use in VB6).
Currently, I have this method to compare two numbers
Private Function ETForGreaterThan(ByVal query As IQueryable(Of T), ByVal propertyValue As Object, ByVal propertyInfo As PropertyInfo) As IQueryable(Of T) Dim e As ParameterExpression = Expression.Parameter(GetType(T), "e")
As you can see, I give it an IQueryable collection and it add a where clause to it, base on a property and a value. Y can construct Lessthan, LessOrEqualThan etc equivalents as System.Linq.Expressions.Expression has this operators predefined.How can I transform this code to do the same with strings? System.Linq.Expressions.Expression don't give me a predefined operator like "contains" or "startwith"?
I came accross the code below in a book. I prefer displaying my data in Winforms instead of the Console which the boook uses but I have little understanding of console codes and how to convert them to Winforms.[code]....
I just want to parse simple expressions like IIF(FVAL(PFC) = TRUE, (IIF((ORGVAL(BAS, "2012/12/31") + ORGVAL(DA)) < 6500, (FVAL(BAS) + FVAL(DA)) * 12%, 780)), 0)`After parsing this I should be able to know what functions contains what parameters.
[Code]...
I'm stuck with .Net Framework 2.0, so no Linq or lambda expression goodies for me. Also I want to include the code in my custom library and not just reference it. Can anyone point me to some good library or code.
I just need to parse and not evaluate the expression and find what tokens are in use. After finding the tokens I need to change the expression string before parsing, like if the function ORGVAL is used then the parameter passed has has to be prefixed by an underscore. Like ORGVAL(BAS) will transform to ORGVAL(_BAS). Some functions can have tow parameters like ORGVAL(BAS, "2012/12/31") and this will transform to ORGVAL(_BAS, "2012/12/31")
NOTE: IF THERE ARE OTHER WAYS OF DOING IT PLEASE LET ME KNOW. I WOULD LOVE TO AVOID A PARSER AND LEXER.
Anyone knows where I can download binary search tree for VB.Net ? I'm working on a small project for my company and I'm thinking of using BST as a sorting tool.I used to do BST using C++ and I was using linked list. I'm not sure if that can be done in VB.Net but is there any other ways? any input and comments are welcome.
I am not the original author of this software project and the code is poorly documented. I am mainly a Java/C++ developer.The program displays the tree structure and allows files and folder to be selected. The program is getting errors with FileSystemTreeView when trying to return nodes on a system with a reserved partition.Here is what is happening: tree.SelectedNode = tree.Nodes(0) 'returns error with system reserved partition.calling, GetDriveList() will properly return all the drive letters - and not throw an error. Only when trying to get a tree.Node() or tree.load() is the error occurring.
private void SomeMethod() { IsBusy = true; var bg = new BackgroundWorker(); bg.DoWork += (sender, e) =>
[code]....
However, I'd like to be able to implement a method like SomeMethod from the C# example in VB.net. Likely this means wrapping the Backgroundworker in another class (which is something I want to do for dependency injection and unit testing anyway).
In debug mode I get into a line that evaluates to false because the expression cannot be evaluated because of "Cannot evaluate expression because the code of the current method is optimized." Program does not assert or error out. If Item.Length then . . . (Here when I hover the mouse it displays "Cannot evaluate expression because the code of the current method is optimized"). What interesting is that it only occurs in one of .vb files.BTW, I'm programming in Compact Framework.
I have a class with a static list of keys, and I have a static method called Remove() that removes a key from that list.Now what I understand from the contracts post conditions is that as the programmer of the class, I guarantee that the current public method does something specific, in this case : removing the element of the list.
Here's what I've written:
private static List<Keys> m_usedKeys; // private list of keys public static void Remove(Keys _key) {
[code]....
What I'm trying to "Ensure" here, is that the Remove() method removes the key for real from the list (Yes this might be a trivial example, but I get the error there.)when I write the Contract.Ensures() line, VS2010 gives me the following error :
Error 3 Detected expression statement evaluated for potential side-effect in contracts of method 'LibJungleTimer.KeyBind.Remove(System.Windows.Forms.Keys)'. (Did you mean to put the expression into a Requires, Ensures, or Invariant call?) C:UsersJoelDocumentsProgrammationJTJungleTimerLibJungleTimerKeyBind.cs 51
I think this error says that the expression m_usedKeys.remove(_key); has a potential side-effect. In fact, it has a side-effect, it removes a key from the list!If I try to write something like this instead :
