Get property from object and check if it contains value

Question

I am trying to use get property from object and check if that property contains certain value:

Method to get property looks like:

   public static object GetProp(object obj, string propName, value)
    {
        return obj.GetType().GetProperty(propName).GetValue(obj).Contains(value);
    }

This will get me object value.

And usage is (or actualy what i am trying to achive is):

     string value = this._predicateFilter.GetValueOrDefault(refName, string.Empty);
        if (!string.IsNullOrEmpty(value))
        {
            predicate.And(c => Assets.Extensions.GetProp(c, "name", "value to compare"));
        } 

I am getting an exception:

'object' does not contain a definition for 'Contains' and the best
extension method overload 'Queryable.Contains<string>
(IQueryable<string>, string)' requires a receiver of type 
'IQueryable<string>'    

And I think problem is something with linq and entity framework cant execute that method inside its body.

I could use nasty solution like:

        string firstname = this._predicateFilter.GetValueOrDefault("Firstname", string.Empty);
        if (!string.IsNullOrEmpty(firstname))
        {
            predicate.And(c => c.Firstname.Contains(firstname));
        }

        string lastname = this._predicateFilter.GetValueOrDefault("Lastname", string.Empty);
        if (!string.IsNullOrEmpty(lastname))
        {
            predicate.And(c => c.Lastname.Contains(lastname));
        }

Witch works fine but, i wold preffer less code, what am I missing?

Oh and im using

var predicate = PredicateBuilder.New<Candidate>();

from linqKit

Answer 1

Type.GetProperty doesn´t return the properties value , but the PropertyInfo for that property itself. What you want is to get the properties value for a given instance - in your case for obj . So use this in your GetProp -method:

return obj.GetType().GetProperty(propName).GetValue(obj);

Answer 2

PropertyInfo.GetValue returns an object which you are trying to use as an IQueryable<T> .

The code is telling you exactly what the error is object does not contain a (extension)method for Contains . Also in the updated code you missed the identifier off of value in the method signature and have the return type as object when you will always be returning a bool .

So fix those errors and before calling Contains cast it to an IQueryable<T> :

public static bool GetProp(object obj, string propName, string value)
{
    object o = obj.GetType().GetProperty(propName).GetValue(obj);

    IQueryable<object> queryable = o as IQueryable<object>;
    if (queryable != null)
    {
        return queryable.Contains(value);
    }

    return false; //Some other default
}

Answer 3

Try the following:

public static bool PropEquals<TProp>(object obj, string propName, TProp valueToTest)
{
    return EqualityComparer<TProp>.Default.
       Equals(valueToTest, obj.GetType().GetProperty(propName).GetValue(obj));
}

...

string value = this._predicateFilter.GetValueOrDefault(refName, string.Empty);
if (!string.IsNullOrEmpty(value))
{
    predicate.And(c => Assets.Extensions.PropEquals(c, "name", "value to compare"));
}

The PropEquals returns a true or false depending on whether the property whose name you supplied is equal to the value that you supplied.