Property name to lambda expression

Question

I have some code which I would like to refactor, but I don't know how to do it. The code in question repeats itself, except for an expression which varies.

The code:

Expression<Func<SearchModel, bool>> first = null;
if (first == null)
{
    if (equal && not)
        first = c1 => c1.Address.PostalCode != newTerm;
    else if (equal)
        first = c1 => c1.Address.PostalCode == newTerm;
    else if (not)
        first = c1 => !c1.Address.PostalCode.Contains(newTerm);
    else
        first = c1 => c1.Address.PostalCode.Contains(newTerm);
}
else
{
    if (equal && not)
        first = first.Or(c1 => c1.Address.PostalCode != newTerm);
    else if (equal)
        first = first.Or(c1 => c1.Address.PostalCode == newTerm);
    else if (not)
        first = first.Or(c1 => !c1.Address.PostalCode.Contains(newTerm));
    else
        first = first.Or(c1 => c1.Address.PostalCode.Contains(newTerm));
}

equal and not are Boolean values.

This code is repeated several times, except that c1.Address.PostalCode could be c1.Address.City, or even c1.User.PhoneNumber.

Can I somehow refactor this so that I can use a method and inject the c1.Address.PostalCode? Something like this:

if (equal && not)
    first = c1 => <variable> != newTerm;
...
else if (not)
    first = c1 => !<variable>.Contains(newTerm);

It looks like this post is what I'm looking for:

Property Name to Lambda Expression C#

But I need to go a little further, because the Address property is a class itself, which of course has properties, one of which is PostalCode.

You could use reflection but you would need to have some more if statement if the property type is a collection or not because of the contains. — Franck, Jan 11 '18 at 16:29
@Franck The code expects the property value to be a string, not a collection. It's doing a string contains check. — Servy, Jan 11 '18 at 16:42
@Servy Thanks for the link. Indeed that's what I was looking for. (It would have helped had I known what to search!) I've managed to pass my expression into a method, but I'm unsure what to do with it. I'm passing a `Expression>` into the method. When I debug and watch the value, it shows it is `{smodel => smodel.User.ContactLastName}`, but I don't know how to use that in my code `first = c1 => c1.User.ContactLastName == newTerm`. — Marc Levesque, Jan 11 '18 at 20:39
There's an example right in the answer in the duplicate of how to use the method. — Servy, Jan 11 '18 at 20:43
@Servy I don't see it. I've copied all your code, using the same variable names, and I'm passing "magic" to my method. I don't see how to use "magic" once inside the method though. — Marc Levesque, Jan 11 '18 at 20:51
@Servy That won't work because first is type `Expression>` and magic is type `Expression>`. — Marc Levesque, Jan 11 '18 at 21:07
@MarcLevesque The reason you're calling compose is to turn your mapping from a search model to a property value and your mapping from a property value to a boolean into a mapping from a search model to a boolean. So the return value of `Compose` *will* be an `Expression>` for you. — Servy, Jan 11 '18 at 21:25

Property name to lambda expression

0 Answers0