I was trying to generate a simple Lambda Expression at runtime with no luck... something like this:
var result = queryableData.Where(item => item.Name == "Soap")
Here is my example class and a fixture queryable:
public class Item
{
public int Id { get; set; }
public string Name { get; set; }
}
IQueryable<Item> queryableData = ...;
Then I generate a lambda expression at runtime correct code follows:
//"item" in "item =>..."
var item = Expression
.Parameter(typeof(Item), "item");
//property of my item, this is "item.Name"
var prop = Expression
.Property(item, "Name");
//then "Soap" in '... => item.Name=="Soap"'
var value = Expression.Constant("Soap");
//equality expression "==" in my primer
var equals = Expression.Equal(prop, value);
//then lambda
var lambda = Expression.Lambda<Func<Item, bool>>(equals, item);
//and here are the results
var results = queryableData.Where(lambda);
Big thanks to dtb for advice!
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);