Expression Tree Tutorial - Knowledge Base (KB)
557 results in tag: c#
Using a Linq Expression tree, find an event.
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
Expression Trees in C#: Serializing and Deserializing
Is there a way to Deserialize Expressions in C#, I would like to store Expressions in a Database and load them at run time.
asked by Alexandre Brisebois
Parsing of Lambda Expression Trees
I am trying to use Lambda Expressions in a project to map to a third party query API. So, I'm parsing the Expression tree by hand....If I pass in a lambda expression like:...p => p.Title == "title" ...everything works....However, if my lambda expression l...
asked by Keith Fitzgerald
How can I retrieve the field value for a type ExpressionType.MemberAccess?
I am parsing an Expression Tree. Given a NodeType of ExpressionType.MemberAccess, how do I get the value of that Field? ...From C# MSDN docs: MemberAccess is A node that represents reading from a field or property. ...A code snippet would be incredibly, ...
asked by Keith Fitzgerald
Within a generic extension method, how do I apply OrderBy to an IQueryable using a string column name?
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
In a C# Expression tree, how can I set a field value?
Given:...FieldInfo field = <some valid string field on type T>; ParameterExpression targetExp = Expression.Parameter(typeof(T), "target"); ParameterExpression valueExp = Expression.Parameter(typeof(string), "value"); ...How do I compile a lambda expressio...
asked by TheSoftwareJedi
I'm not sure how to make an expression tree using IEnumerableTSource>. 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
In C#, how can I build an Expression Tree by parsing XML?
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
How do you feed bits of a LINQ query into a function in LINQ to SQL?
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 make a deep property expression tree / lambda from a string
Given a string: "Person.Address.Postcode" I want to be able to get/set this postcode property on an instance of Person. How can I do this? My idea was to split the string by "." and then iterate over the parts, looking for the property on the previous typ...
asked by Andrew Bullock
Genetic Programming with C# Dynamic Trees
I have some public user defined classes with relations between their members and also several methods with specific and generic signatures....I would like to be able to store and manipulate custom control flow over these classes (plus CLR classes) using b...
asked by wilsonlarg
To pick an anonymous type, establish a LINQ Expression Tree.
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
Dummies' expression trees?
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
How do I change an ExpressionFuncSomeType>> to an ExpressionFuncOtherType>> in C#?
I have used C# expressions before based on lamdas, but I have no experience composing them by hand. Given an ...Expression<Func<SomeType, bool>> originalPredicate..., I want to create an ...Expression<Func<OtherType, bool>> translatedPredicate.......In th...
asked by Michiel van Oosterhout
Property name retrieved 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
Partially executing an IQueryable query while leaving the remainder 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
Is there a simple method to convert a string (lambda expression) 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
Refactoring this Generic GetByID function in C# LINQ to SQL
I wrote the following method....public T GetByID(int id) { var dbcontext = DB; var table = dbcontext.GetTable<T>(); return table.ToList().SingleOrDefault(e => Convert.ToInt16(e.GetType().GetProperties().First().GetValue(e, null)) == id); } ...
asked by Andreas Grech
How do you break down an equation into separate variable formulas?
How to convert an equation into formulas for individual variables? I am thinking about a math equations like:...c^2 = a^2 + b^2 ...I would like to have a function that could process any formula, and give me the individual variable formulas. The above equ...
asked by Bobby Ortiz
How can I parse random strings into expression trees in C#?
In a project that I'm working on I have to work with a rather weird data source. I can give it a "query" and it will return me a DataTable. But the query is not a traditional string. It's more like... a set of method calls that define the criteria that I ...
asked by Vilx-