How to convert a String to its equivalent LINQ Expression Tree?
Solution 1:
Would the dynamic linq library help here? In particular, I'm thinking as a Where
clause. If necessary, put it inside a list/array just to call .Where(string)
on it! i.e.
var people = new List<Person> { person };
int match = people.Where(filter).Any();
If not, writing a parser (using Expression
under the hood) isn't hugely taxing - I wrote one similar (although I don't think I have the source) in my train commute just before xmas...
Solution 2:
Another such library is Flee
I did a quick comparison of Dynamic Linq Library and Flee and Flee was 10 times faster for the expression "(Name == \"Johan\" AND Salary > 500) OR (Name != \"Johan\" AND Salary > 300)"
This how you can write your code using Flee.
static void Main(string[] args)
{
var context = new ExpressionContext();
const string exp = @"(Person.Age > 3 AND Person.Weight > 50) OR Person.Age < 3";
context.Variables.DefineVariable("Person", typeof(Person));
var e = context.CompileDynamic(exp);
var bob = new Person
{
Name = "Bob",
Age = 30,
Weight = 213,
FavouriteDay = new DateTime(2000, 1, 1)
};
context.Variables["Person"] = bob;
var result = e.Evaluate();
Console.WriteLine(result);
Console.ReadKey();
}
Solution 3:
void Main()
{
var testdata = new List<Ownr> {
//new Ownr{Name = "abc", Qty = 20}, // uncomment this to see it getting filtered out
new Ownr{Name = "abc", Qty = 2},
new Ownr{Name = "abcd", Qty = 11},
new Ownr{Name = "xyz", Qty = 40},
new Ownr{Name = "ok", Qty = 5},
};
Expression<Func<Ownr, bool>> func = Extentions.strToFunc<Ownr>("Qty", "<=", "10");
func = Extentions.strToFunc<Ownr>("Name", "==", "abc", func);
var result = testdata.Where(func.ExpressionToFunc()).ToList();
result.Dump();
}
public class Ownr
{
public string Name { get; set; }
public int Qty { get; set; }
}
public static class Extentions
{
public static Expression<Func<T, bool>> strToFunc<T>(string propName, string opr, string value, Expression<Func<T, bool>> expr = null)
{
Expression<Func<T, bool>> func = null;
try
{
var type = typeof(T);
var prop = type.GetProperty(propName);
ParameterExpression tpe = Expression.Parameter(typeof(T));
Expression left = Expression.Property(tpe, prop);
Expression right = Expression.Convert(ToExprConstant(prop, value), prop.PropertyType);
Expression<Func<T, bool>> innerExpr = Expression.Lambda<Func<T, bool>>(ApplyFilter(opr, left, right), tpe);
if (expr != null)
innerExpr = innerExpr.And(expr);
func = innerExpr;
}
catch (Exception ex)
{
ex.Dump();
}
return func;
}
private static Expression ToExprConstant(PropertyInfo prop, string value)
{
object val = null;
try
{
switch (prop.Name)
{
case "System.Guid":
val = Guid.NewGuid();
break;
default:
{
val = Convert.ChangeType(value, prop.PropertyType);
break;
}
}
}
catch (Exception ex)
{
ex.Dump();
}
return Expression.Constant(val);
}
private static BinaryExpression ApplyFilter(string opr, Expression left, Expression right)
{
BinaryExpression InnerLambda = null;
switch (opr)
{
case "==":
case "=":
InnerLambda = Expression.Equal(left, right);
break;
case "<":
InnerLambda = Expression.LessThan(left, right);
break;
case ">":
InnerLambda = Expression.GreaterThan(left, right);
break;
case ">=":
InnerLambda = Expression.GreaterThanOrEqual(left, right);
break;
case "<=":
InnerLambda = Expression.LessThanOrEqual(left, right);
break;
case "!=":
InnerLambda = Expression.NotEqual(left, right);
break;
case "&&":
InnerLambda = Expression.And(left, right);
break;
case "||":
InnerLambda = Expression.Or(left, right);
break;
}
return InnerLambda;
}
public static Expression<Func<T, TResult>> And<T, TResult>(this Expression<Func<T, TResult>> expr1, Expression<Func<T, TResult>> expr2)
{
var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
return Expression.Lambda<Func<T, TResult>>(Expression.AndAlso(expr1.Body, invokedExpr), expr1.Parameters);
}
public static Func<T, TResult> ExpressionToFunc<T, TResult>(this Expression<Func<T, TResult>> expr)
{
var res = expr.Compile();
return res;
}
}
LinqPad has the Dump()
method
Solution 4:
You might take a look at the DLR. It allows you to evaluate and execute scripts inside .NET 2.0 application. Here's a sample with IronRuby:
using System;
using IronRuby;
using IronRuby.Runtime;
using Microsoft.Scripting.Hosting;
class App
{
static void Main()
{
var setup = new ScriptRuntimeSetup();
setup.LanguageSetups.Add(
new LanguageSetup(
typeof(RubyContext).AssemblyQualifiedName,
"IronRuby",
new[] { "IronRuby" },
new[] { ".rb" }
)
);
var runtime = new ScriptRuntime(setup);
var engine = runtime.GetEngine("IronRuby");
var ec = Ruby.GetExecutionContext(runtime);
ec.DefineGlobalVariable("bob", new Person
{
Name = "Bob",
Age = 30,
Weight = 213,
FavouriteDay = "1/1/2000"
});
var eval = engine.Execute<bool>(
"return ($bob.Age > 3 && $bob.Weight > 50) || $bob.Age < 3"
);
Console.WriteLine(eval);
}
}
public class Person
{
public string Name { get; set; }
public int Age { get; set; }
public int Weight { get; set; }
public string FavouriteDay { get; set; }
}
Of course this technique is based on runtime evaluation and code cannot be verified at compile time.