How can I use dynamic Lambda in dynamic LINQ

Question

In my search for the expression parser, I found the Dynamic LINQ API . I want to use this API so that the end user can specify some criteria for validating business objects.

So my first attempt to use the library succeeds with the following Unit test

var x = Expression.Parameter(typeof(int), "x");
var list = Expression.Parameter(typeof(List<int>), "list");
var e = DynamicExpression.ParseLambda(new[] { x, list }, null, "list.Any(it == x)");
var compiledExpression = e.Compile();

var myList = new List<int> { 24, 46, 67, 78 };
Assert.AreEqual(false, compiledExpression.DynamicInvoke(2, myList));
Assert.AreEqual(true, compiledExpression.DynamicInvoke(24, myList));

However, I want to have a slightly more complex syntax as I want to change this

list.Any(it == x)     // OK

at

list.Any(i => i == x) // Raises error: No property or field 'i' exists in type 'int'

The second syntax, however, will allow me to nest lambda (which is my ultimate goal) as follows:

list1.All(i => list2.Any(j => j == i))

Does anyone know how to configure Dynamic.cs to support this syntax?

Answer 1

After hours of debugging, I found the solution myself.

unit test :

var list1 = Expression.Parameter(typeof(List<int>), "list1");
var list2 = Expression.Parameter(typeof(List<int>), "list2");
var e = DynamicExpression.ParseLambda(new[] { list1, list2 }, null, "list2.All(i => list1.Any(j => j == i))");
var compiledExpression = e.Compile();

var myList1 = new List<int> { 24, 46, 67, 78 };
var myList2 = new List<int> { 46 };
var myList3 = new List<int> { 8 };
Assert.AreEqual(true, compiledExpression.DynamicInvoke(myList1, myList2));
Assert.AreEqual(false, compiledExpression.DynamicInvoke(myList1, myList3));

, Dynamic.cs:

1) TokenId Lambda

2) IDictionary named internals ExpressionParser. ExpressionParser

3) ( 971)

if (symbols.TryGetValue(token.text, out value) ||
    externals != null && externals.TryGetValue(token.text, out value)) {

if (symbols.TryGetValue(token.text, out value) ||
externals != null && externals.TryGetValue(token.text, out value) ||
internals.TryGetValue(token.text, out value)) {

4) ( 1151)

if (member == null)
    throw ParseError(errorPos, Res.UnknownPropertyOrField,
       id, GetTypeName(type));

if (member == null)
{
    if(token.id == TokenId.Lambda && it.Type == type)
    {
        // This might be an internal variable for use within a lambda expression, so store it as such
        internals.Add(id, it);
        NextToken();
        var right = ParseExpression();
        return right;
    }
    else
    {
        throw ParseError(errorPos, Res.UnknownPropertyOrField,
            id, GetTypeName(type));                        
    }
}

5) ( 1838)

case '=':
NextChar();
if (ch == '=') {
    NextChar();
    t = TokenId.DoubleEqual;
}
else {
    t = TokenId.Equal;
}
break;

case '=':
NextChar();
if (ch == '=') {
    NextChar();
    t = TokenId.DoubleEqual;
}
else if(ch == '>')
{
    NextChar();
    t = TokenId.Lambda;
}
else {
    t = TokenId.Equal;
}
break;