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    Session: Loading Entities

    There are various methods with many overloads that allow users to download documents from a database and convert them to entities. This article will cover the following methods:

    Load

    The most basic way to load a single entity is to use one of the Load methods.

    TResult Load<TResult>(string id);
    Task<TResult> LoadAsync<TResult>(string id);
    Parameters
    id string Identifier of a document that will be loaded.
    Return Value
    TResult Instance of TResult or null if a document with a given ID does not exist.

    Example

    Employee employee = session.Load<Employee>("employees/1");
    Employee employee = await asyncSession.LoadAsync<Employee>("employees/1");

    Note

    In 4.x RavenDB, only string identifiers are supported. If you are upgrading from 3.x, this is a major change, because in 3.x non-string identifiers are supported.

    Load with Includes

    When there is a 'relationship' between documents, those documents can be loaded in a single request call using the Include + Load methods.

    ILoaderWithInclude<object> Include(string path);

ILoaderWithInclude<T> Include<T>(Expression<Func<T, string>> path);

ILoaderWithInclude<T> Include<T>(Expression<Func<T, IEnumerable<string>>> path);

ILoaderWithInclude<T> Include<T, TInclude>(Expression<Func<T, string>> path);

ILoaderWithInclude<T> Include<T, TInclude>(Expression<Func<T, IEnumerable<string>>> path);
    Parameters
    path string or Expression Path in documents in which the server should look for 'referenced' documents.
    Return Value
    ILoaderWithInclude The Include method by itself does not materialize any requests but returns loader containing methods such as Load.

    Example I

    We can use this code to also load an employee which made the order.

    // loading 'products/1'
// including document found in 'Supplier' property
Product product = session
    .Include("Supplier")
    .Load<Product>("products/1");

Supplier supplier = session.Load<Supplier>(product.Supplier); // this will not make server call
    // loading 'products/1'
// including document found in 'Supplier' property
Product product = await asyncSession
    .Include("Supplier")
    .LoadAsync<Product>("products/1");

Supplier supplier = await asyncSession.LoadAsync<Supplier>(product.Supplier); // this will not make server call

    Example II

    // loading 'products/1'
// including document found in 'Supplier' property
Product product = session
    .Include<Product>(x => x.Supplier)
    .Load<Product>("products/1");

Supplier supplier = session.Load<Supplier>(product.Supplier); // this will not make server call
    // loading 'products/1'
// including document found in 'Supplier' property
Product product = await asyncSession
    .Include<Product>(x => x.Supplier)
    .LoadAsync<Product>("products/1");

Supplier supplier = await asyncSession.LoadAsync<Supplier>(product.Supplier); // this will not make server call

    Load - multiple entities

    To load multiple entities at once, use one of the following Load overloads.

    Dictionary<string, TResult> Load<TResult>(IEnumerable<string> ids);
    Task<Dictionary<string, TResult>> LoadAsync<TResult>(IEnumerable<string> ids);
    Parameters
    ids IEnumerable Multiple document identifiers to load
    Return Value
    Dictionary<string, TResult> Instance of Dictionary which maps document identifiers to TResult or null if a document with given ID doesn't exist. 

    Dictionary<string, Employee> employees = session.Load<Employee>(new[]
{
    "employees/1",
    "employees/2",
    "employees/3"
});
    Dictionary<string, Employee> employees = await asyncSession.LoadAsync<Employee>(new[]
{
    "employees/1",
    "employees/2",
});

    LoadStartingWith

    To load multiple entities that contain a common prefix, use the LoadStartingWith method from the Advanced session operations.

    T[] LoadStartingWith<T>(
    string idPrefix,
    string matches = null,
    int start = 0,
    int pageSize = 25,
    string exclude = null,
    string startAfter = null);

void LoadStartingWithIntoStream(
    string idPrefix,
    Stream output,
    string matches = null,
    int start = 0,
    int pageSize = 25,
    string exclude = null,
    string startAfter = null);
    Task<T[]> LoadStartingWithAsync<T>(
    string idPrefix,
    string matches = null,
    int start = 0,
    int pageSize = 25,
    string exclude = null,
    string startAfter = null);

Task LoadStartingWithIntoStreamAsync(
    string idPrefix,
    Stream output,
    string matches = null,
    int start = 0,
    int pageSize = 25,
    string exclude = null,
    string startAfter = null);
    Parameters
    idPrefix string prefix for which the documents should be returned
    matches string pipe ('|') separated values for which document IDs (after 'idPrefix') should be matched ('?' any single character, '*' any characters)
    start int number of documents that should be skipped
    pageSize int maximum number of documents that will be retrieved
    exclude string pipe ('|') separated values for which document IDs (after 'idPrefix') should not be matched ('?' any single character, '*' any characters)
    skipAfter string skip document fetching until given ID is found and return documents after that ID (default: null)
    Return Value
    TResult[] Array of entities matching given parameters.
    Stream Output entities matching given parameters as a stream.

    Example I

    // return up to 128 entities with Id that starts with 'employees'
Employee[] result = session
    .Advanced
    .LoadStartingWith<Employee>("employees", null, 0, 128);
    // return up to 128 entities with Id that starts with 'employees'
Employee[] result = (await asyncSession
    .Advanced
    .LoadStartingWithAsync<Employee>("employees", null, 0, 128))
    .ToArray();

    Example II

    // return up to 128 entities with Id that starts with 'employees/' 
// and rest of the key begins with "1" or "2" e.g. employees/10, employees/25
Employee[] result = session
    .Advanced
    .LoadStartingWith<Employee>("employees/", "1*|2*", 0, 128);
    // return up to 128 entities with Id that starts with 'employees/' 
// and rest of the key begins with "1" or "2" e.g. employees/10, employees/25
Employee[] result = (await asyncSession
    .Advanced
    .LoadStartingWithAsync<Employee>("employees/", "1*|2*", 0, 128))
    .ToArray();

    Stream

    Entities can be streamed from the server using one of the following Stream methods from the Advanced session operations.

    Streaming query results does not support the include feature. Learn more in How to Stream Query Results.

    Information

    Entities loaded using Stream will be transient (not attached to session).

    IEnumerator<StreamResult<T>> Stream<T>(IQueryable<T> query);

IEnumerator<StreamResult<T>> Stream<T>(IQueryable<T> query, out StreamQueryStatistics streamQueryStats);

IEnumerator<StreamResult<T>> Stream<T>(IDocumentQuery<T> query);

IEnumerator<StreamResult<T>> Stream<T>(IRawDocumentQuery<T> query);

IEnumerator<StreamResult<T>> Stream<T>(IRawDocumentQuery<T> query, out StreamQueryStatistics streamQueryStats);

IEnumerator<StreamResult<T>> Stream<T>(IDocumentQuery<T> query, out StreamQueryStatistics streamQueryStats);

IEnumerator<StreamResult<T>> Stream<T>(string startsWith, string matches = null, int start = 0, int pageSize = int.MaxValue, string startAfter = null);
    Task<IAsyncEnumerator<StreamResult<T>>> StreamAsync<T>(IQueryable<T> query);

Task<IAsyncEnumerator<StreamResult<T>>> StreamAsync<T>(IQueryable<T> query, out StreamQueryStatistics streamQueryStats);

Task<IAsyncEnumerator<StreamResult<T>>> StreamAsync<T>(IDocumentQuery<T> query);

Task<IAsyncEnumerator<StreamResult<T>>> StreamAsync<T>(IRawDocumentQuery<T> query);

Task<IAsyncEnumerator<StreamResult<T>>> StreamAsync<T>(IRawDocumentQuery<T> query, out StreamQueryStatistics streamQueryStats);

Task<IAsyncEnumerator<StreamResult<T>>> StreamAsync<T>(IDocumentQuery<T> query, out StreamQueryStatistics streamQueryStats);

Task<IAsyncEnumerator<StreamResult<T>>> StreamAsync<T>(string startsWith, string matches = null, int start = 0, int pageSize = int.MaxValue, string startAfter = null);
    Parameter Type Description
    startsWith string prefix for which documents should be streamed
    matches string pipe ('|') separated values for which document IDs should be matched ('?' any single character, '*' any characters)
    start int number of documents that should be skipped
    pageSize int maximum number of documents that will be retrieved
    skipAfter string skip document fetching until a given ID is found and returns documents after that ID (default: null)
    StreamQueryStats streamQueryStats (out parameter) Information about the streaming query (amount of results, which index was queried, etc.)
    Return Type Description
    IEnumerator<StreamResult> Enumerator with entities.
    streamQueryStats (out parameter) Information about the streaming query (amount of results, which index was queried, etc.)

    Example I

    Stream documents for a ID prefix:

    IEnumerator<StreamResult<Employee>> enumerator = session
    .Advanced
    .Stream<Employee>("employees/");

while (enumerator.MoveNext())
{
    StreamResult<Employee> employee = enumerator.Current;
}
    Raven.Client.Util.IAsyncEnumerator<StreamResult<Employee>> enumerator = await asyncSession
    .Advanced
    .StreamAsync<Employee>("employees/");

while (await enumerator.MoveNextAsync())
{
    StreamResult<Employee> employee = enumerator.Current;
}

    Example 2

    Fetch documents for a ID prefix directly into a stream:

    using (var outputStream = new MemoryStream())
{
    session
        .Advanced
        .LoadStartingWithIntoStream("employees/", outputStream);
}
    using (var outputStream = new MemoryStream())
{
    await asyncSession
        .Advanced
        .LoadStartingWithIntoStreamAsync("employees/", outputStream);
}

    IsLoaded

    To check if an entity is attached to a session, e.g. it has been loaded previously, use the IsLoaded method from the Advanced session operations.

    IsLoaded checks if you've already tried to load a document during the current session.
    If you try to load a document that no longer exists with the Load method (perhaps it has been deleted),
    IsLoaded will then return true because IsLoaded shows that you've already tried to load the non-existent document.

    bool IsLoaded(string id);
    Parameters
    id string Entity ID for which the check should be performed.
    Return Value
    bool Indicates if an entity with a given ID is loaded.

    Example

    bool isLoaded = session.Advanced.IsLoaded("employees/1"); // false
Employee employee = session.Load<Employee>("employees/1");
isLoaded = session.Advanced.IsLoaded("employees/1"); // true
    bool isLoaded = asyncSession.Advanced.IsLoaded("employees/1"); // false
Employee employee = await asyncSession.LoadAsync<Employee>("employees/1");
isLoaded = asyncSession.Advanced.IsLoaded("employees/1"); // true

    see on GitHub

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