Question

I have a method which takes an array of strings as parameter and queries against a collection property which is also a collection of strings. If that property has one of the values inside the string array passed as parameter, it should be returned.

Here is my code:

public IEnumerable<BlogPost> GetAll(string[] tags, 
    bool includeUnapprovedEntries = false) {

    foreach (var tag in tags) {
        foreach (var blogPost in GetAll(includeUnapprovedEntries).
            ToList().Where(x => x.Tags.Any(t => t == tag))) {
            yield return blogPost;
        }
    }
}

Note:

Here is the complete code:

https://github.com/tugberkugurlu/MvcBloggy/blob/master/src/MvcBloggy.Data/DataAccess/SqlServer/BlogPostRepository.cs

This does the job but it just doesn’t seem right. I could have made this better with some extension methods but couldn’t figure out what would do the trick and make this implementation right.

Any idea?

Answer 1

How about this:

public IEnumerable<BlogPost> GetAll(string[] tags,
    bool includeUnapprovedEntries = false) {

    return GetAll(includeUnapprovedEntries)
        .Where(x => x.Tags.Any(t => tags.Contains(t));
}

You may want to call ToList() to materialize the result. Note that this will (hopefully!) result in an IN query in SQL; if you have a large number of tags, I wouldn’t be surprised if that failed. (I don’t know how the Entity Framework handles that situation.) I believe it should be okay with smaller numbers of tags though.

Note that whether or not this is supported may depend on the version of the entity framework you’re using; I seem to remember that some transformations like this (using Contains on a “local” collection) to translate to IN in SQL) have improved over time. Make sure you develop against the same version you’ll be deploying against 🙂