Expression.Lambda and query generation at runtime, nested property “Where” example

落爺英雄遲暮 提交于 2019-12-05 03:28:37
Fernando Matsumoto

(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);

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);
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