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)
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:
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:
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:
I've build a large program with many references. F.e.:
System.Data.DataSetExtensions System.Linq.Dynamic
I've to write a Dynamic Linq Expression: [URL]
In my case: Dim query As IEnumerable = ds.Sales.Where(strWhere)
But with System.Data.DataSetExtensions Where is misinterpreted. The compiler expects (Datarow, Integer, Boolean). If I delete System.Data.DataSetExtensions everything is ok with this expression, but I get many other errors, so I need this reference. What can I do that the Where is interpreted correctly?
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.
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..
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 need to represent the following query using LINQ:
DECLARE @PurchasedInventoryItemID Int = 2 DECLARE @PurchasedInventorySectionID Int = 0 DECLARE @PurchasedInventoryItem_PurchasingCategoryID Int = 3 DECLARE @PurchasedInventorySection_PurchasingCategoryID Int = 0
[code]....
Now, I know that a query in .NET doesnt look like this, this is my test in the SQL Design Studio. Naturally VB.NET variables will be used in place of the SQL local variables.My problem is this: All of the conditions after "WHERE" are optional. In that a query might be made that uses one, some, all, or none of the conditions. V.PropertyID and V.Value can also appear any number of times.In VB.NET I can make this query easy enough by simply concatenating strings, and using a loop to append the "V.PropertyID/V.Value" conditions.I can also make a Stored Procedure in MS SQL, which is easy enough.However, I want to accomplish this using LINQ.
Forgive my ignorance on this.I have this LINQ Query:Dim ngBikersDataContext As New CarBikeWalkDataContext
bikersList = (From c In ngBikersDataContext.Reg_Bikers _ Order By c.L_Name _ Select New Bikers() With { _ .BikerID = c.BikerID, _ .F_Name = c.F_Name, _
[Code]...
with the error "Overload resolution failed because no accesible 'Select' accepts this number of arguments." Over the "NEW" I get an error " ')'expected."
I'm attempting to build a function that will return a regex that is dynamically created.The regex to create will be a range check between two numbers. So far I've got something similar to this (not finished as yet).Is this approach valid, or is there an easier way that I'm overlooking?
Public Shared Function Range(ByVal Minimum As Integer, ByVal Maximum As Integer) As String Return "^([" & Minimum.ToString.PadLeft(2, "0") & "]" & Microsoft.VisualBasic.StrDup(Minimum.ToString.Length, "[0-9]") & "|2[0-4][0-9]|25[0-5])$"
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"?
Is there any way to make a RegularExpressionValidator render itself using display:block, instead of display:inline in its style attribute, when setting the Display property to "Display='Dynamic'"?
I have tried setting it in the stylesheet but this gets overwritten when it is rendered on the page.
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.
I'm having a little trouble converting some LINQ to VB.[code]Online code translators are not helping, and my unfamiliarly with VB LINQ is not very good.
I need to test a logical expression held in a string to see if it evaluate to TRUE or FALSE.(the strig is built dynamically)For example the resulting string may contain "'dog'<'cat' OR (1>4 AND 4<6)". There are no variables in the string, it will logically evaluate. It will only contain simple operators = > < >< >= <= and AND , OR and Open and Close Brackets, string constants and numbers. (converted to correct syntax && || etc.)
I currently acheive this by creating a jscipt function and compiling it into a .dll. I then reference the .dll in my VB.NET project.
class ExpressionEvaluator { function Evaluate(Expression : String) { return eval(Expression); } }
Is there a simpler method using built in .NET functions or Lamdba expressions.
Where can I find complex LINQ examples made using VB.NET Lambda Expression syntax?During my searches I always found 101 LINQ Samples but they use the other notation and for me is not always clear how to transform that code into a lambda expression.
[code]The LINQ query going into "result" is incomplete because I'm stumped at what is happening there. I expect FirstOrDefault to refer to refer to a single Child object at that point in the expression, but it refers to a collection of child objects. Why? What is the best way to get a list of parents that have no associated child or have a child fitting a particular condition? (My actual code will have one child max, so this sample code is not representative.)I just don't understand what the collection of FirstOrDefault could be referring to. It should really be just 1 value or nothing at all times.
