Querying: Using Indexes

You can query time series indexes using session.Query and session.Advanced.DocumentQuery, and enhance the queries using LINQ expressions.

• Definitions

  • session.Query
    

    IRavenQueryable<T> Query<T, TIndexCreator>() where TIndexCreator 
         : AbstractCommonApiForIndexes, new();

  • DocumentQuery
    

    IDocumentQuery<T> DocumentQuery<T, TIndexCreator>() where TIndexCreator 
         : AbstractCommonApiForIndexes, new();

• Parameters

  Parameters	Description
  T	Results Container
  TIndexCreator	Index

• Return Values

  As return values are specific to each index, we need to define a matching results container.

  In the following sample we define a map index that collects three fields from the "HeartRate" time series, a "Results" container for the results, and an index query that uses both.

  public class SimpleIndex : AbstractTimeSeriesIndexCreationTask<Employee>
  {
  
      public class Result
      {
          public double HeartBeat { get; set; }
          public DateTime Date { get; set; }
          public string User { get; set; }
          public string Tag { get; set; }
      }
  
      public SimpleIndex()
      {
          AddMap(
              "HeartRates",
              timeSeries => from ts in timeSeries
                            from entry in ts.Entries
                            select new
                            {
                                HeartBeat =
                                  entry.Values[0],
                                entry.Timestamp.Date,
                                User = ts.DocumentId,
                                Tag = entry.Tag
                            });
      }
  }

  // Query time-series index using session.Query
  using (var session = store.OpenSession())
  {
      List<SimpleIndex.Result> results = 
          session.Query<SimpleIndex.Result, SimpleIndex>()
          .ToList();
  }

• Querying an Index
  To query a time series index, call session.Query or session.Advanced.DocumentQuery.
  

  • session.Query
  • DocumentQuery

  // Query time-series index using session.Query
  using (var session = store.OpenSession())
  {
      List<SimpleIndex.Result> results = 
          session.Query<SimpleIndex.Result, SimpleIndex>()
          .ToList();
  }

  // Query time-series index using DocumentQuery
  using (var session = store.OpenSession())
  {
      List<SimpleIndex.Result> results = 
          session.Advanced.DocumentQuery<SimpleIndex.Result, SimpleIndex>()
          .ToList();
  }

• Enhancing Index Queries

  • When you call session.Query, You can add LINQ expressions to your query.
    

    // Enhance the query using LINQ expressions
    var chosenDate = new DateTime(2020, 5, 20);
    using (var session = store.OpenSession())
    {
        List<SimpleIndex.Result> results = 
            session.Query<SimpleIndex.Result, SimpleIndex>()
            .Where(w => w.Date < chosenDate)
            .OrderBy(o => o.HeartBeat)
            .ToList();
    }

  • You can add LINQ-like expressions to a DocumentQuery as well.
    

    // Query time-series index using DocumentQuery with Linq-like expressions
    using (var session = store.OpenSession())
    {
        List<SimpleIndex.Result> results = 
            session.Advanced.DocumentQuery<SimpleIndex.Result, SimpleIndex>()
            .WhereEquals("Tag", "watches/fitbit")
            .ToList();
    }

• Async queries
  You can run asynchronous queries as well.

  // Time-series async index query using session.Query
  using (var session = store.OpenAsyncSession())
  {
      List<SimpleIndex.Result> results = 
          await session.Query<SimpleIndex.Result, SimpleIndex>()
          .ToListAsync();
  }