Expression Tree Tutorial - Knowledge Base (KB)
252 results in tag: linq
Identify an event via a Linq Expression tree
The compiler usually chokes when an event doesn't appear beside a ...+=... or a ...-=..., so I'm not sure if this is possible....I want to be able to identify an event by using an Expression tree, so I can create an event watcher for a test. The syntax wo...
asked by user1228
Assignment in .NET 3.5 expression trees
Is it possible to encode an assignment into an expression tree?
asked by Eric Smith
How do I build a Linq Expression Tree that compares against a generic object?
I have an IQueryable and an object of type T....I want to do IQueryable().Where(o => o.GetProperty(fieldName) == objectOfTypeT.GetProperty(fieldName))...so ......public IQueryable<T> DoWork<T>(string fieldName) where T : EntityObject { ... T...
asked by JTew
How do I apply OrderBy on an IQueryable using a string column name within a generic extension method?
public static IQueryable<TResult> ApplySortFilter<T, TResult>(this IQueryable<T> query, string columnName) where T : EntityObject { var param = Expression.Parameter(typeof(T), "o"); var body = Expression.PropertyOrField(param,columnName); var sor...
asked by JTew
How do I create an expression tree calling IEnumerable<TSource>.Any(...)?
I am trying to create an expression tree that represents the following:...myObject.childObjectCollection.Any(i => i.Name == "name"); ...Shortened for clarity, I have the following:...//'myObject.childObjectCollection' is represented here by 'propertyExp' ...
asked by flesh
How do I Create an Expression Tree by Parsing Xml in C#?
I am looking to create an expression tree by parsing xml using C#. The xml would be like the following:...<Expression> <If> <Condition> <GreaterThan> <X> <Y> </GreaterThan> </Condition> <Expression /> <If> <Else> <Expression />...
asked by SharePoint Newbie
Best way to call an instance method in Expression Trees?
What is the best way to call an instance method within an Expression Tree? My current solution is something like this for an interface method "object GetRowValue(rowIndex)" of the interface IColumn....public static Expression CreateGetRowValueExpression( ...
asked by Rauhotz
Expression.Or, The parameter 'item' is not in scope
I am trying to write a static function to Or two expressions, but recieve the following error:...The parameter 'item' is not in scope....Description: An unhandled exception occurred during the execution of the current web request. Please review the ...
asked by ccook
In LINQ to SQL, how do you pass parts of a LINQ query into a function
Is it possible to pass parts of a linq Query into a function? I want create a common interface for my DAL that always uses the same query interface. For example, ...List<T> Get(Join j, Where w, Select s){ return currentDataContext<T>.Join(j).Wh...
asked by Arron S
How to create LINQ Expression Tree to select an anonymous type
I would like to generate the following select statement dynamically using expression trees:...var v = from c in Countries where c.City == "London" select new {c.Name, c.Population}; ...I have worked out how to generate...var v = from c in ...
asked by Tom Deloford
Expression trees for dummies?
I am the dummy in this scenario....I've tried to read on Google what these are but I just don't get it. Can someone give me a simple explanation of what they are and why they're useful?...edit: I'm talking about the LINQ feature in .Net.
asked by Dave
Retrieving Property name from lambda expression
Is there a better way to get the Property name when passed in via a lambda expression? Here is what i currently have....eg. ...GetSortingInfo<User>(u => u.UserId); ...It worked by casting it as a memberexpression only when the property was a string. beca...
asked by Schotime
how to change the type of the parameter in an Expression?
since i am using POCOS in my domain, i want my repository to be able to received Expression filters of the type of my POCOS and change the parameter in the expression to be the of type of my LINQ tables, my fields have the same name as my members so i was...
asked by Oscar Cabrero
Performing part of a IQueryable query and deferring the rest to Linq for Objects
I have a Linq provider that sucessfully goes and gets data from my chosen datasource, but what I would like to do now that I have my filtered resultset, is allow Linq to Objects to process the rest of the Expression tree (for things like Joins, projection...
asked by Tim Jarvis
Print out Linq Expression Tree Hierarchy
The ...dynamic language runtime (DLR)... has some pretty cool code for Expression's, including some very nice code to print out Expression trees which I want to use so that:...int a = 1; int b = 2; Expression<Func<int, int>> expression = (c) => a + (b * ...
asked by anon
Is there an easy way to parse a (lambda expression) string into an Action delegate?
I have a method that alters an "Account" object based on the action delegate passed into it:...public static void AlterAccount(string AccountID, Action<Account> AccountAction) { Account someAccount = accountRepository.GetAccount(AccountID); AccountAct...
asked by Whisk
How do I dynamically create an Expression<Func<MyClass, bool>> predicate?
How would I go about using an Expression Tree to dynamically create a predicate that looks something like......(p.Length== 5) && (p.SomeOtherProperty == "hello") ...So that I can stick the predicate into a lambda expression like so......q.Where(myDynamic...
asked by Senkwe
Convert SQL Query back to Linq Expression programmatically
Is it possible to somehow programmatically convert a sql query to a linq expression tree? The sql query is supposed to be generated by this linq query, so I'm thinking of it as a poor man's serialization\deserialization of linq queries to t-sql format....
asked by Valentin Vasilyev
How do I make a LINQ expression to call a method?
I've been playing around with the ...DLR... a bit and am a bit stuck on calling methods. For example, suppose I want to make an expression to push something onto a stack:...class StackInfo{ protected Stack<SomeClass> _stack; public Expression P...
asked by Jason Baker
expression trees linq get value of a parameter?
AddOptional<tblObject>(x =>x.Title, objectToSend.SupplementaryData); private static void AddOptional<TType>(Expression<Func<TType,string>> expr, Dictionary<string, string> dictionary) { string propertyName; string propertyValue; Expression e...
asked by Tadeusz Wójcik
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