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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);
Parameters
idstringIdentifier of a document that will be loaded.
Return Value
TResultInstance of TResult or null if a document with a given ID does not exist.

Example​

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

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
pathstring or ExpressionPath in documents in which the server should look for 'referenced' documents.
Return Value
ILoaderWithIncludeThe 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

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

Load - multiple entities​

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

Dictionary<string, TResult> Load<TResult>(IEnumerable<string> ids);
Parameters
idsIEnumerable<string>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"
});

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);
Parameters
idPrefixstringprefix for which the documents should be returned
matchesstringpipe ('|') separated values for which document IDs (after 'idPrefix') should be matched ('?' any single character, '*' any characters)
startintnumber of documents that should be skipped
pageSizeintmaximum number of documents that will be retrieved
excludestringpipe ('|') separated values for which document IDs (after 'idPrefix') should not be matched ('?' any single character, '*' any characters)
skipAfterstringskip document fetching until given ID is found and return documents after that ID (default: null)
Return Value
TResult[]Array of entities matching given parameters.
StreamOutput 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);

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);

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.

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);
ParameterTypeDescription
startsWithstringprefix for which documents should be streamed
matchesstringpipe ('|') separated values for which document IDs should be matched ('?' any single character, '*' any characters)
startintnumber of documents that should be skipped
pageSizeintmaximum number of documents that will be retrieved
skipAfterstringskip document fetching until a given ID is found and returns documents after that ID (default: null)
StreamQueryStatsstreamQueryStats (out parameter)Information about the streaming query (amount of results, which index was queried, etc.)
Return TypeDescription
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;
}

Example 2​

Fetch documents for a ID prefix directly into a stream:

using (var outputStream = new MemoryStream())
{
  session
      .Advanced
      .LoadStartingWithIntoStream("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
idstringEntity ID for which the check should be performed.
Return Value
boolIndicates 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