Exploration Queries

Exploration queries can be applied using -

• Query.Filter
• DocumentQuery.Filter
• RQL's filter keyword

The added filtering is parsed and executed by RavenDB's Javascript engine.

The provided filtering operations resemble those implemented by where and can be further enhanced by Javascript functions of your own.
Read here about creating and using your own Javascript function in your filters.

filter can be applied to a Collection query, like in:

from Employees as e 
filter e.Address.Country = 'USA'

it can also be applied to queries handled by an index, e.g. -

// in a dynamic query via an auto-index  
from Employees as e 
where e.Title = 'Sales Representative'  
filter e.Address.Country = 'USA'

// in a query that uses an index explicitly  
from index 'Orders/ByCompany' 
filter Count > 10

Both in a collection query and in a query handled by an index, the entire retrieved dataset is scanned and filtered.
This helps understand when exploration queries should be used, why a Limit should be set for the number of filtered records, and when where should be preferred:

• Query.Filter
  

  IRavenQueryable<T> Filter<T>(this IRavenQueryable<T> source, 
                               Expression<Func<T, bool>> predicate, 
                               int limit = int.MaxValue);

  Parameters	Type	Description
  source	IRavenQueryable<T>	Filter, defined as an IRavenQueryable extension method
  predicate	Expression<Func<T, bool>>	The condition by which retrieved records are filtered
  limit	int	Limits the number of filtered records (Recommended) Default: all retrieved records

• DocumentQuery.Filter
  

  IDocumentQuery<T> Filter(Action<IFilterFactory<T>> builder, 
                           int limit = int.MaxValue);

  Parameters	Type	Description
  builder	Action<IFilterFactory<T>>	Your filter
  limit	int	Limits the number of filtered records (Recommended) Default: all retrieved records

• RQL

  • In an RQL query, use:
    The filter keyword, followed by the filtering condition.
    The filter_limit option, followed by the max number of records to filter.
  • E.g. -
    

    from Employees as e 
    where e.Title = 'Sales Representative'  
    filter e.Address.Country = 'USA' // filter the retrieved dataset
    filter_limit 500 // limit the number of filter records

With Collection Queries

Use filter with a collection query to scan and filter the entire collection.

var result = session.Query<Employee>()
    .Filter(f => f.Address.Country == "USA", limit: 500)
    .SingleOrDefault();

result = session.Advanced.DocumentQuery<Employee>()
    .Filter(p => p.Equals(a => a.Address.Country, "USA"), limit: 500)
    .SingleOrDefault();

result = session.Advanced.RawQuery<Employee>
    ("from Employees as e " +
       "filter e.Address.Country = 'USA' " +
       "filter_limit 500").SingleOrDefault();

With Queries that Use an Index

Use filter after a where clause to filter the results retrieved by an index query.

var emp = session.Query<Employee>()
    .Where(w => w.Title == "Sales Representative")
    .Filter(f => f.Address.Country == "USA", limit: 500)
    .SingleOrDefault();

emp = session.Advanced.DocumentQuery<Employee>()
      .WhereEquals(w => w.Title, "Sales Representative")
      .Filter(p => p.Equals(a => a.Address.Country, "USA"), limit: 500)
      .SingleOrDefault();

emp = session.Advanced.RawQuery<Employee>
    ("from Employees as e" +
     "where e.Title = $title" +
     "filter e.Address.Country = $country" +
     "filter_limit $limit")
    .AddParameter("title", "Sales Representative")
    .AddParameter("country", "USA")
    .AddParameter("limit", 500)
    .SingleOrDefault();

With Projections

The filtered results can be projected using select, like those of any other query.

var emp1 = session
    .Query<Employee>()
    .Filter(f => f.Address.Country == "USA", limit: 500)
    .Select(x => new
     {
        FullName = x.FirstName + " " + x.LastName
     })
    .ToList();

var fullName = new string[]{
    "FirstName",
    "LastName"
};

var emp2 = session.Advanced.DocumentQuery<Employee>()
      .Filter(p => p.Equals(a => a.Address.Country, "USA"), limit: 500)
      .SelectFields<Employee>(fullName)
      .ToList();

var emp3 = session.Advanced.RawQuery<Employee>
    ("from Employees as e" +
        "filter startsWith(e.FirstName, 'A')" +
        "select { FullName: e.FirstName + ' ' + e.LastName }");

With User-Defined Javascript Functions (declare)

You can define a Javascript function as part of your query using the declare keyword, and use it as part of your filter condition to freely adapt the filtering to your needs.

Here is a simple example:

// declare a Javascript function
declare function titlePrefix(r, prefix) 
{ 
    // Add whatever filtering capabilities you like
    return r.Title.startsWith(prefix)
} 

from Employees as e 

// Filter using the function you've declared
filter titlePrefix(e, $prefix)
filter_limit 100