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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.

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);

Parameters
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 (out parameter) Information about the streaming query (amount of results, which index was queried, etc.)  
Return Value
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;
}
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);
}

Remarks

Information

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

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.

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