Expression.Lambda and query generation at runtime,

问题:

I found very nice answer on a question about building Expression Tree for Where query.

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

Can someone help me and show me how this example could be implemented in the scenario with nested property. I mean instead of:

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

With that solution:

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);

How can I build the tree for the following?

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

回答1:

(This answer was originally posted by the OP in the question.)

The problem can be solved with:

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

var dataExpr = Expression.Property(item, "Data");

var prop = Expression.Property(dataExpr, "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);

回答2:

This is the same answer as posted above, but I find this more readable in terms of visualizing an expression tree:

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

var lambda = Expression.Lambda<Func<Item, bool>>(
    Expression.Equal(
        Expression.Property(
            Expression.Property(
                parameterItem, 
                "Data"
            ), 
            "Name"
        ), 
        Expression.Constant("Soap")
    ), 
    parameterItem
);

var result = queryableData.Where(lambda);