Expression.Lambda and query generation at runtime, simplest “Where” example

by

In the following query

var result = query.Where(item => item.Name == "Soap")

the lambda expression is

item => item.Name == "Soap"

You only need to construct this part, not the Where call which accepts an expression tree.

The expression tree for the lambda expression looks like this:

                     Lambda
                      /  \
                   Equal  Parameter
                   /   \    item
              Property  \
               "Name"   Constant
                 |       "Soap"
             Parameter         
               item

In code:

var item = Expression.Parameter(typeof(Item), "item");

var prop = Expression.Property(item, "Name");

var soap = Expression.Constant("Soap");

var equal = Expression.Equal(prop, soap);

var lambda = Expression.Lambda<Func<Item, bool>>(equal, item);

var result = queryableData.Where(lambda);

More Related Contents:

  1. How do I create an expression tree to represent ‘String.Contains(“term”)’ in C#?
  2. lambda expression to sort on min values in a group
  3. Retrieving Property name from lambda expression
  4. How do I apply OrderBy on an IQueryable using a string column name within a generic extension method?
  5. converting a .net Func to a .net Expression
  6. Mutating the expression tree of a predicate to target another type
  7. LINQ to Entities only supports casting EDM primitive or enumeration types with IEntity interface
  8. Can I specify my explicit type comparator inline?
  9. Replace parameter in lambda expression
  10. Lambda variable capture in loop – what happens here? [duplicate]
  11. Wrapping StopWatch timing with a delegate or lambda?
  12. Weak event handler model for use with lambdas
  13. Pass expression parameter as argument to another expression
  14. How do I pronounce “=>” as used in lambda expressions in .Net [closed]
  15. What is the Efficiency and Performance of LINQ and Lambda Expression in .Net?
  16. How to Combine two lambdas [duplicate]
  17. Expression of type ‘System.Int32’ cannot be used for return type ‘System.Object’
  18. Peculiar overload resolution with while (true)
  19. How to unsubscribe from an event which uses a lambda expression?
  20. Why do some C# lambda expressions compile to static methods?
  21. Access the value of a member expression
  22. Max return value if empty query
  23. Group by with multiple columns using lambda
  24. How does PredicateBuilder work
  25. How do I dynamically create an Expression predicate?
  26. How to use Expression Tree to safely access path of nullable objects?
  27. Expression for Type members results in different Expressions (MemberExpression, UnaryExpression)
  28. Getting names of local variables (and parameters) at run-time through lambda expressions
  29. How do I translate an expression tree of one type to a different expression type?
  30. Getting the object out of a MemberExpression?

Leave a Comment