Session: Querying: How to Perform Queries Lazily

In some situations, query execution must be delayed. To cover such a scenario, Lazily and many other query extensions have been introduced.

Lazily and LazilyAsync

// Define a lazy query
Lazy<IEnumerable<Employee>> lazyEmployees = session
  .Query<Employee>()
  .Where(x => x.FirstName == "Robert")
   // Add a call to 'Lazily'
  .Lazily();

IEnumerable<Employee> employees = lazyEmployees.Value; // Query is executed here

Parameters
onEval	Action<IEnumerable<TResult>>	An action that will be performed on the query results.

Return Value
Lazy<IEnumerable<TResult>>	Lazy query initializer returning query results.

Example

• Sync
• Async

Lazy<IEnumerable<Employee>> employeesLazy = session
  .Query<Employee>()
  .Where(x => x.FirstName == "Robert")
  .Lazily();

IEnumerable<Employee> employees = employeesLazy.Value; // query will be executed here

Lazy<Task<IEnumerable<Employee>>> employeesLazy = session
  .Query<Employee>()
  .Where(x => x.FirstName == "Robert")
  .LazilyAsync();

IEnumerable<Employee> employees = await employeesLazy.Value; // query will be executed here

Counts

// Define a lazy count query
Lazy<int> lazyCount = session
  .Query<Employee>()
  .Where(x => x.FirstName == "Robert")
   // Add a call to 'CountLazily'
  .CountLazily();

int count = lazyCount.Value; // Query is executed here

Return Value
Lazy<int>	Lazy query initializer returning a count of matched documents.

Example

// Define a lazy count query
Lazy<Task<int>> lazyCount = asyncSession
  .Query<Employee>()
  .Where(x => x.FirstName == "Robert")
   // Add a call to 'CountLazilyAsync'
  .CountLazilyAsync();

int count = await lazyCount.Value; // Query is executed here

Suggestions

// Define a lazy DocumentQuery
Lazy<int> lazyCount = session.Advanced
  .DocumentQuery<Employee>()
  .WhereEquals(x => x.FirstName, "Robert")
   // Add a call to 'CountLazily'
  .CountLazily();

int count = lazyCount.Value; // DocumentQuery is executed here

Return Value
Lazy<Dictionary<string, SuggestionResult>>	Lazy query initializer containing a dictionary with suggestions for matching executed query

Example

// Define a lazy suggestion query
Lazy<Dictionary<string, SuggestionResult>> lazySuggestions = session
  .Query<Product>()
  .SuggestUsing(builder => builder.ByField(x => x.Name, "chaig"))
   // Add a call to 'ExecuteLazy'
  .ExecuteLazy();

Dictionary<string, SuggestionResult> suggest = lazySuggestions.Value; // Query is executed here
List<string> suggestions = suggest["Name"].Suggestions;

Facets

// Define a lazy suggestion query
Lazy<Task<Dictionary<string, SuggestionResult>>> lazySuggestions = asyncSession
  .Query<Employee>()
  .SuggestUsing(builder => builder.ByField("Name", "chaig"))
   // Add a call to 'ExecuteLazyAsync'
  .ExecuteLazyAsync();

Dictionary<string, SuggestionResult> suggest = await lazySuggestions.Value; // Query is executed here
List<string> suggestions = suggest["Name"].Suggestions;

Return Value
Lazy<Dictionary<string, FacetResult>>	Lazy query initializer containing a dictionary with facet results matching executed query

Example

// Define a lazy DocumentQuery
Lazy<Dictionary<string, SuggestionResult>> lazySuggestions = session.Advanced
  .DocumentQuery<Employee>()
  .SuggestUsing(builder => builder.ByField("Name", "chaig"))
   // Add a call to 'ExecuteLazy'
  .ExecuteLazy();

Dictionary<string, SuggestionResult> suggest = lazySuggestions.Value; // DocumentQuery is executed here
List<string> suggestions = suggest["FullName"].Suggestions;