You are currently browsing legacy 4.0 version of documentation. Click here to switch to the newest 6.2 version.
    We can help you with migration to the latest RavenDB
    Contact Us Now
    See on GitHub

    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 

    Lazy<IEnumerable<T>> Lazily<T>();

Lazy<IEnumerable<T>> Lazily<T>(Action<IEnumerable<T>> onEval);

Lazy<Task<IEnumerable<T>>> LazilyAsync<T>();

Lazy<Task<IEnumerable<T>>> LazilyAsync<T>(Action<IEnumerable<T>> onEval);
    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

    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 

    Lazy<int> CountLazily<T>();

Lazy<Task<int>> CountLazilyAsync<T>(CancellationToken token = default(CancellationToken));
    Return Value
    Lazy Lazy query initializer returning a count of matched documents.

    Example

    Lazy<int> countLazy = session
    .Query<Employee>()
    .Where(x => x.FirstName == "Robert")
    .CountLazily();

int count = countLazy.Value; // query will be executed here

    Suggestions 

    Lazy<Dictionary<string, SuggestionResult>> ExecuteLazy(Action<Dictionary<string, SuggestionResult>> onEval = null);

Lazy<Task<Dictionary<string, SuggestionResult>>> ExecuteLazyAsync(Action<Dictionary<string, SuggestionResult>> onEval = null);
    Return Value
    Lazy<Dictionary<string, SuggestionResult>> Lazy query initializer containing a dictionary with suggestions for matching executed query

    Example

    Lazy<Dictionary<string, SuggestionResult>> suggestLazy = session
    .Query<Employee>("Employees_ByFullName")
    .SuggestUsing(builder => builder.ByField("FullName", "johne"))
    .ExecuteLazy();

Dictionary<string, SuggestionResult> suggest = suggestLazy.Value; // query will be executed here
List<string> suggestions = suggest["FullName"].Suggestions;

    Facets 

    Lazy<Dictionary<string, FacetResult>> ExecuteLazy(Action<Dictionary<string, FacetResult>> onEval = null);

Lazy<Task<Dictionary<string, FacetResult>>> ExecuteLazyAsync(Action<Dictionary<string, FacetResult>> onEval = null);
    Return Value
    Lazy<Dictionary<string, FacetResult>> Lazy query initializer containing a dictionary with facet results matching executed query

    Example

    Lazy<Dictionary<string, FacetResult>> facetsLazy = session
    .Query<Camera>("Camera/Costs")
    .AggregateUsing("facets/CameraFacets")
    .ExecuteLazy();

Dictionary<string, FacetResult> facets = facetsLazy.Value; // query will be executed here
FacetResult results = facets["Manufacturer"];

    related articlesRelated Articles

    Session

    Home / Docs / Client Api / Session / Querying / How To Perform Queries Lazily