Creating MemberAcces with ExpressionTree to a complex type

Question

Creating MemberAcces with ExpressionTree to a complex type

c# expression expression-trees lambda linq

Question

I'd like to dynamically create a MemberAcess Expression to a deeper level then 1 (recursively):

public class Job
{
    public string Name { get; set; }
    public int Salary { get; set; }
}
public class Employee
{
    public string Name { get; set; }
    public Job Job { get; set; }
}

And I want to dynamically create a list of MemberAccesExpressions for each property in Employee and each property in Employee's complex members, the outcome should be something like this:

MemberAccesExpression[] {
    { e => e.Name },
    { e => e.Job.Name },
    { e => e.Job.Name }
}

This is a pseudo code of what I got:

List list = new List();
public Expression<Func<TModel, dynamic>> CreateME<TModel>(TModel model)
{
        var type = typeof (TModel);
        var properties = type.GetProperties();
        foreach (var prop in properties)
        {
            // I want to ignore collections
            if (typeof(ICollection).IsAssignableFrom(prop.PropertyType)) continue;

            // Recall for complex property
            if (prop.PropertyType.Namespace != "System")
            {
                // CreateME(model, ) // THIS IS WHEN I DON'T KNOW WHAT TO DO
                continue;
            }

            var param = Expression.Parameter(type, "x");
            var memberAccess = Expression.PropertyOrField(param, prop.Name);
            list.Add(Expression.Lambda<Func<TModel, dynamic>>(memberAccess, param));
        }
}

How do I make this a recursive method? I thought of adding an optional parameter named (TModel model, Expression> baseMemberAccess = null) and somehow concat the member expression to baseMemberAccess if it's not null.

P.S. is there's a better way to determine if a Type is not atomic type then this (prop.PropertyType.Namespace != "System") ? (not int,float,string,etc...)

Appreciate any help, Adam

An edit for trying to lay it more simply:

If I want to create an expression tree of a member access to Employee.Name this is what I do:

        var param = Expression.Parameter(type, "x");
        var memberAccess = Expression.PropertyOrField(param, memberName);
        return Expression.Lambda<Func<TModel, TMember>>(memberAccess, param);

What is the equivalent to this for a member access to Employee.Job.Salary ?

Adam Tal

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Adam Mills · Accepted Answer · 6/22/2012 7:34:00 PM

public IEnumerable<Expression<Func<TModel, dynamic>>> CreateME<TModel>()
    {
        var stack = new Stack<StackItem>();
        var type = typeof(TModel);
        var parameterExpression = Expression.Parameter(type, "x");
        stack.Push(new StackItem(typeof(TModel), parameterExpression));

        while (stack.Count > 0)
        {
            var currentItem = stack.Pop();
            var properties = currentItem.PropertyType.GetProperties();
            foreach (var property in properties)
            {
                if (IsComplexProperty(property))
                    stack.Push(new StackItem(property.PropertyType, Expression.PropertyOrField(currentItem.AccessChainExpression, property.Name)));
                else
                {
                    yield return GetSimplePropertyExpression<TModel>(parameterExpression, currentItem.AccessChainExpression, property.Name);
                }
            }
        }


    }

    private static Expression<Func<TModel, dynamic>> GetSimplePropertyExpression<TModel>(ParameterExpression lhs, Expression accessChain, string propertyName)
    {
        var memberAccess = Expression.Convert(Expression.PropertyOrField(accessChain, propertyName), typeof(object));
        return Expression.Lambda<Func<TModel, dynamic>>(memberAccess, lhs);
    }

    private static bool IsComplexProperty(PropertyInfo p)
    {
        return !typeof (ICollection).IsAssignableFrom(p.PropertyType) && p.PropertyType.Namespace != "System";
    }


    class StackItem
    {
        public StackItem(Type propertyType, Expression accessChainExpression)
        {
            PropertyType = propertyType;
            AccessChainExpression = accessChainExpression;
        }

        public Type PropertyType { get; private set; }
        public Expression AccessChainExpression { get; private set; }
    }

Im sure it can be improved, but this should work.

Creating MemberAcces with ExpressionTree to a complex type

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