Question

I have a method that excepts an IEnumerable<T> and a lambda expression that describes the field to be used to compare a linq-to-sql collection to an array. The method returns the matching records.

public IEnumerable<ZipCode> match<T>(IEnumerable<T> values, 
        Func<ZipCode, T> matchPhrase) {
    return (from zipCode in _table
            where values.Contains<T>(matchPhrase)
            select zipCode).Distinct();
}

I’m getting the error:

Argument type 'Func<ZipCode, T>' is not assignable to parameter type 'T'

The method would be called like so (where values is an IEnumerable<string> and x.zipcode is a string):

var zipCodes = _zipCodeRepository.match(values, x => x.zipcode)

UPDATE

Based on John’s suggestion of using HashSet<T> I have changed my code however I’m getting a different error now

Method ‘System.Object DynamicInvoke(System.Object[])’ has no supported translation to SQL.

I think I may not have been clear on my question and I think I’m using the wrong method signature to get my desired outcome. Let me explain with a more simple code example:

public IEnumerable<ZipCode> match(IEnumerable<string> values) {
    return (from zipCode in _table
            where values.Contains(zipCode.zipcode)
            select zipCode).Distinct();
}

I am tyring to accomplish this but with anonymous types. I would like to pass in the field to be used in the Contains() via a lambda. So zipCode.zipcode would be passed into the method as the second argument: x => x.zipcode

Answer 1

I suspect you wanted to call the delegate:

return (from zipCode in _table
        where values.Contains(matchPhrase(zipCode))
        select zipCode).Distinct();

Mind you, that would potentially be very expensive. You might want to create a set first:

HashSet<T> valueSet = new HashSet<T>(values);
return _table.Where(x => valueSet.Contains(matchPhrase(x))
             .Distinct();

(I’ve removed the query expression here as it was doing more harm than good in terms of readability.)