Raven4 - Query help - Find Tags In Posts

[Andy Knight]

Hi all,

Just a simple problem. Given the following code, I'm trying to create queries such as:

1. Find all posts that have a specific tag

2. List all tags and count of posts for each.

public class Post

{

    public List<string> Tags {get;set;}

    // shortened for brevity

}

So I looked through Oren's old posts such as this one:

https://ayende.com/blog/4466/that-no-sql-thing-modeling-documents-in-a-document-database

but if I write the following simple query in Raven studio, it fails:

from Posts 

as p

select tag in p.Tags

select new {tag, count = 1}

"Raven.Server.Documents.Queries.Parser.QueryParser+ParseException: 3:13 Expected end of query but got: in"

Whats the correct syntax to extract all items in a sub collection so that I can group and filter them?

regards

Andy

[Oren Eini (Ayende Rahien)]

Hi,

The issue is a bit complex. Because you want two separate things, and they deal with the data differently.

The first query, first all posts with a specific tag:

from Posts where Tags = $tag

This will find all the documents with the right tag. The output of this is the the full documents that has this tag.

For getting count of posts in a specific tag, use:

from Posts

group by Tags[]

where Tags[] = $tag

select key() as Tag, count() as Count

This will use "Tags[]" to have a separate value per tag list in the post and create a map/reduce index behind the scenes to maintain this

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[Andy Knight]

Sorry to drag up an old post, I've been off project.

I'm trying to convert the above count query into a compiled index. I have the following:

    public class PostTagsCountIndex : AbstractIndexCreationTask<Post>

    {

        public class Result

        {

            public string Tag { get; set; }

            public int Count { get; set; }

        }

        public PostTagsCountIndex()

        {

            Map = posts => from p in posts

                          from t in p.Tags

                          select new { Tag = t, Count = 1 };

            Reduce = results => from result in results

                                group result by result into g

                                select new Result

                                {

                                    Tag = g.Key,

                                    Count = g.Sum()

                                };

        }

    }

Its doesnt want to convert g.Key (Post) into a string. But should g.Key be the grouped Tag string?

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[Arkadiusz Palinski]

Since you're trying to get the Count per Tag you should group by result.Tag

from result in results

                                group result by result.Tag into g

                                select new Result

                                {

                                    Tag = g.Key,

                                    Count = g.Sum()

                                };

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[Grisha Kotler]

Also missing:

 

- public class PostTagsCountIndex : AbstractIndexCreationTask<Post, PostTagsCountIndex.Result>

- Count = g.Sum(x => x.Count)

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[Andy Knight]

Thankyou both, that worked perfectly.

Andy