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Indexes: Indexing Counters

Syntax​

In order to index counter values, create an index that inherits from AbstractCountersIndexCreationTask. Next, choose one of these two methods which take the index expression:

protected void AddMapForAll(Expression<Func<IEnumerable<CounterEntry>, IEnumerable>> map)

protected void AddMap(string counter, Expression<Func<IEnumerable<CounterEntry>, IEnumerable>> map)

AddMapForAll indexes all the counters in the indexed documents. AddMap only indexes the counters with the specified name.

Examples of indexes using each method:

private class MyCounterIndex : AbstractCountersIndexCreationTask<Company>
{
  public MyCounterIndex()
  {
      AddMap("Likes", counters => from counter in counters
                                      select new
                                      {
                                          Likes = counter.Value,
                                          Name = counter.Name,
                                          User = counter.DocumentId
                                      });
  }
}

AbstractJavaScriptCountersIndexCreationTask​

Creating an index inheriting from AbstractJavaScriptCountersIndexCreationTask allows you to write your map and reduce functions in JavaScript.
Learn more about JavaScript indexes here.

public class AbstractJavaScriptCountersIndexCreationTask : AbstractCountersIndexCreationTask
{
  public HashSet<string> Maps;
  protected string Reduce;
}
PropertyTypeDescription
MapsHashSet<string>The set of javascript map functions
ReducestringThe javascript reduce function

Example:

private class MyMultiMapCounterIndex : AbstractJavaScriptCountersIndexCreationTask
{
  public MyMultiMapCounterIndex()
  {
      Maps = new HashSet<string>
      {
          @"counters.map('Blogposts', 'Likes', function (counter) {
              return {
                  Likes: counter.Value,
                  Name: counter.Name,
                  Blog Post: counter.DocumentId
              };
          })"
      };
  }
}

CounterNamesFor​

While indexes inheriting from AbstractIndexCreationTask cannot index counter values, the CounterNamesFor method is available which returns the names of all counters for a specified document:

IEnumerable<string> CounterNamesFor(object doc);

Example of index using CounterNamesFor:

public class Companies_ByCounterNames : AbstractIndexCreationTask<Company>
{
  public class Result
  {
      public string[] CounterNames { get; set; }
  }

  public Companies_ByCounterNames()
  {
      Map = employees => from e in employees
                         let counterNames = CounterNamesFor(e)
                         select new Result
                         {
                             CounterNames = counterNames.ToArray()
                         };
  }
}

Querying the Index​

// return all companies that have 'Likes' counter
List<Company> companies = session
  .Query<Companies_ByCounterNames.Result, Companies_ByCounterNames>()
  .Where(x => x.CounterNames.Contains("Likes"))
  .OfType<Company>()
  .ToList();