Passing property from reflection into expression

Question

I want to loop through my model properties using reflection, and then pass them into a method expecting my property as en expression.

For example, given this model:

public class UserModel
{
    public string Name { get; set; }
}

And this validator class:

public class UserValidator : ValidatorBase<UserModel>
{
    public UserValidator()
    {
        this.RuleFor(m => m.Username);
    }
}

And my ValidatorBase class:

public class ValidatorBase<T>
{
    public ValidatorBase()
    {
        foreach (PropertyInfo property in 
                     this.GetType().BaseType
                         .GetGenericArguments()[0]
                         .GetProperties(BindingFlags.Public | BindingFlags.Insance))
        {
            this.RuleFor(m => property); //This line is incorrect!!
        }
    }

    public void RuleFor<TProperty>(Expression<Func<T, TProperty>> expression)
    {
        //Do some stuff here
    }
}

The issue is with the ValidatorBase() constructor -- given that I have the PropertyInfo for the property I need, what should I pass into as the expression parameter in the RuleFor method, such that it works just like the line in UserValidator() constructor?

Or, should I be using something else besides PropertyInfo to get this to work?

Sergey Kalinichenko · Accepted Answer · 2012-09-06 20:14:57Z

6

I suspect you want:

ParameterExpression parameter = Expression.Parameter(typeof(T), "p");
Expression propertyAccess = Expression.Property(parameter, property);
// Make it easier to call RuleFor without knowing TProperty
dynamic lambda = Expression.Lambda(propertyAccess, parameter);
RuleFor(lambda);

Basically it's a matter of building an expression tree for the property... dynamic typing from C# 4 is just used to make it easier to call RuleFor without explicitly doing that via reflection. You could do it, of course - but you'd need to fetch the RuleFor method, then call MethodInfo.MakeGenericMethod with the property type, then invoke the method.

edited Sep 6, 2012 at 20:14

Sergey Kalinichenko

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answered Sep 6, 2012 at 20:06

Jon Skeet

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