C# - Create An Expression Tree To Do The Same As "StartsWith"?
Dec 29, 2010
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")
[code]....
It works fine and is consumed in this way
query = ETForGreaterThan(query, Value, propertyInfo)
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"?
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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.
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Oct 28, 2011
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)
[Code]...
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Nov 21, 2010
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..
[Code]....
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Nov 19, 2010
I get this error "Late binding operations cannot be converted to an expression tree."
At all my x.NAME) lines !?
<div>Navn: <%: Html.EditorFor(Function(x) x.Name)%></div>
<h3>Adresse</h3>
<div>Linje 1: <%: Html.EditorFor(Function(x) x.Line1)%></div>
[Code].....
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Jul 26, 2010
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:
[Code]...
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Dec 29, 2011
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.
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May 23, 2012
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:
[Code]...
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Mar 7, 2011
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:
[Code]...
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Jun 8, 2012
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.
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Mar 17, 2012
Creating a family tree.
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Oct 29, 2010
[how can i create binary tree for mlm
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Jan 17, 2012
I need to compare two tree-structured reports and show comparison results in a datagridview in vb.net. I think using tree structure should be efficient. But note that I DO NOT use a tree view to display results (I found a lot of help in tree view though). All I want to do is to construct two trees, and then search the trees and compare. I do not know how to write this in vb.net.
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Jan 19, 2010
How can i create an arborescence of folders tree in vb.net?
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Jan 1, 2012
I'm looking for a way to create the treeview structure in memory with a classes, so I can loop through them, like with a collection and easily load the data into a treeview, listview, datagridview or simply work with the data in the background.
There's a treenode class that I could use, but I've noticed that when I have a lot of data in the nodes, it has a lot overhead when for example serializing, because it also saves the checked state, imageindex of the nodes and things like that, which I never need. The saved file is about 10 times bigger than the actual data, which is not acceptable.
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Sep 20, 2011
I have a bunch of objects, they aren't in XML but the xml document would look like this[code]...
The tree is obviously very deep. Does anyone have an algorithm to create this into a jstree, series of "UL" and "LI". It would be christmas if you had the code in vb...but I will be satisfied with just the logic. My thought is to eventually make this into a jsonp web service so I can use jstree to build a tree, but for now im just trying to understand the logic necessary to parse this correctly.
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Jul 14, 2010
I have a bunch of objects, they aren't in XML but the xml document would look like this:
<object>
<path>root</path>
</object>
<object>
[code]....
The tree is obviously very deep. Does anyone have an algorithm to create this into a jstree, series of "UL" and "LI". It would be christmas if you had the code in vb...but I will be satisfied with just the logic. My thought is to eventually make this into a jsonp web service so I can use jstree to build a tree, but for now im just trying to understand the logic necessary to parse this correctly.
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Jun 7, 2010
How to create Dynamic Tree View for an ERP software in VB.Net
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Aug 17, 2010
how to create tree view with multi languages in vb.net
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Jun 12, 2011
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.
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Jun 10, 2011
I have two DataGridViews in one window. The first one displays 2 columns, itemNo and taskWhen I click on a row in this grid, I want to populate the second grid with corresponding material. It is organized so that the itemNo in grid1 is 1, 2, 3, and so on, and so when a row is clicked, I want grid2 to show data that is 1.0, 1.1, 1.2, 2.0, 2.1 and so on. This data is all available in a table that exists within a dataset. However, tableAdapters do not use the .StartsWith function. I am able to get the information from grid1 when it is clicked on using Me.DataGridView1.CurrentRow.Cells(0).Value.ToString but how can I use this to get the data from the table into grid2
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May 30, 2011
I am trying to check if the string starts with certain words before I even add it to my item list, but it doesn't seem to return true even when it should return true.. File I am reading through with my application:
[Constructor.ReplicationHandler]
MeshNames=(ConvexMeshName="",StaticMeshName="52325332",EmitterClassName"")
MeshNames=(ConvexMeshName="",StaticMeshName="3255232",EmitterClassName"")
MeshNames=(ConvexMeshName="",StaticMeshName="644363",EmitterClassName"")
MeshNames=(ConvexMeshName="",StaticMeshName="4636434621646",EmitterClassName"")
MeshNames=(ConvexMeshName="",StaticMeshName="2626352",EmitterClassName"")
[Code]...
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Jan 23, 2012
example how to create a right click on selected node in tree view..example
parentNode = mdiform
childnode1 = child form1
childnode2 = chile form2
which ever i select a different node a corresponding form will appear with a mouseup event.
i must choose first a node to view my contextmenu.
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Aug 3, 2010
In my code I can easily use "where Obj.Feld = String", but using "where Obj.Feld.StartsWith("a")" doesn't work. See the following two functions:
[Code]...
The first function (byFileName) works fine. The second function (LikeFileName) doesn't. Using Startswith I get "Object reference not set to an instance of an object." What am I doing wrong?Database is an array of Objects, a structure consisting of strings
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Jul 10, 2009
i have a situation in which i have to check if the string starts with something and then perform something....First i used "If" as below
If utn.text.startswith("Fuel") then
messagebox.show("Fuel Purchase is selected")
End If
[code]....
Now i have to use Select and Case statements along with startswith...?
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Feb 13, 2011
I am working on my application as I am checking ip using with .StartsWith and .EndsWith method. If the ip is equals then it will equals with US. However I have got an error with end of statement expected error using with this line: [code] I have tried to use "And" instead of "&", but I still get the same error.
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Feb 12, 2009
It is a little like a search and replace, I want to replace any string that contains any substring in parentheses with the same string but the words in parentheses colored RED: Eg
Take this text in TextBox1:
"The Prime Minister (that idiot from Scotland) made a speech today"
and convert to this text in RichTextBox1:
"The Prime Minister (that idiot from Scotland) made a speech today"
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Oct 5, 2010
Can someone tell me please if it is possible to create a datacolumn(LowestPrice), and using something like MIN expression, have this column (LowestPrice) populated with the lowest amount from 3 columns on the same row.[code]If possible could someone please provide the syntax or code for this to work
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Feb 12, 2009
create a regular expression. It is a little like a search and replace, I want to replace any string that contains any substring in parentheses with the same string but the words in parentheses colored RED.
Eg Take this text in TextBox1:
"The Prime Minister (that idiot from Scotland) made a speech today"
and convert to this text in RichTextBox1:
"The Prime Minister (that idiot from Scotland) made a speech today"
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Feb 26, 2009
I want to extract
[code]...
using a regular expression. I have a regex like this:
FROM.*order
which extracts FROM codes WHERE FieldName='ContactMethod' and IsNull(Deactived,'') != 'T' order Also, how can I get rid of the capitalization?
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