ASP NET MVC How to call Count on an attribute then print out a sorted list? - entity-framework

Question

Say I had a class:
public class Post
{
public int PostId { get; set; }
public string Topic { get; set; }
public int UserId { get; set; }
[StringLength(5000)]
public string Body { get; set; }
public DateTime DateCreated { get; set; }
public string Name { get; set; }
public int Votes { get; set; }
}
And for each post, a user could input a topic. for example, if the topics were "Red" "Green" "Blue" and "Yellow", how could I create a list based on how many times those were used?
An example output:
Red | 70
Blue | 60
Green | 40
Yellow| 35
EDIT: How come this doesn't work and gives me an error where I cannot implicitly convert the type?
public List<string> GetPopularTopics(int count)
{
var posts = from p in db.Posts
group p by p.Topic into myGroup
select new
{
Topic = myGroup.Key,
Count = myGroup.Count()
};
return posts.ToList();
}
EDIT 2:
So I tried your solution out Dustin, and I'm getting an error. This is what I used:
public IEnumerable<IGrouping<string,int>> GetPosts()
{
var posts = from p in db.Posts
group p by p.Topic into topicCounts
select new
{
Topic = topicCounts.Key,
Count = topicCounts.Count()
};
return posts.ToList();
}
This is giving me an error under posts.ToList():
Cannot implicitly convert type 'System.Collections.Generic.List' to 'System.Collections.Generic.IEnumerable>'. An explicit conversion exists (are you missing a cast?)

Answer 1

To create the grouping you create an anonymous type such as:
var posts = from p in context.Posts
group p by p.Topic into topicCounts
select new
{
Topic = topicCounts.Key,
Count = topicCounts.Count()
};
Then to work with the date, lets say iterate over it:
foreach(var p in posts)
{
Response.Write(String.Format("{0} - {1}", p.Topic, p.Count));
}

Answer 2

You must create a new type if you do a projection and return it form method!
public class MyCounts
{
public string Topic { get; set; }
public int Count { get; set; }
}
public List<MyCounts> GetPopularTopics(int count)
{
var posts = from p in db.Posts
group p by p.Topic into myGroup
select new MyCounts
{
Topic = myGroup.Key,
Count = myGroup.Count()
};
return posts.ToList();
}

Answer 3

The problem is that you need to use an non anonymous type for your return value.
This query creates an IEnumerable of anonymous types.
var posts = from p in context.Posts
group p by p.Topic into topicCounts
select new
{
Topic = topicCounts.Key,
Count = topicCounts.Count()
};
It's the select new statement that creates the anonymous objects.
What you need to do is to create something that is non anonymous - an object that can be shared within and outside this method.
Like this:
public IEnumerable<TopicAndCount> GetPosts()
{
var posts = from p in context.Posts
group p by p.Topic into topicCounts
select new TopicAndCount
{
Topic = topicCounts.Key,
Count = topicCounts.Count()
};
}
Note the select new TopicAndCount statement and the return value of the enclosing method.
That will solve your problem.