Session: Loading Entities
There are several methods with many overloads that allow users to download documents from the 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.
<T> T load(Class<T> clazz, String id);
Parameters | ||
---|---|---|
id | String |
Identifier of a document that will be loaded. |
Return Value | |
---|---|
T | Instance of T or null if a document with a given ID does not exist. |
Example
Employee employee = session.load(Employee.class, "employees/1");
Note
From RavenDB version 4.x onwards, 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. Learn more in
How To Handle Document Relationships.
See also including counters
and including time series.
ILoaderWithInclude include(String path);
<TResult> Map<String, TResult> load(Class<TResult> clazz, String... ids);
<TResult> Map<String, TResult> load(Class<TResult> clazz, Collection<String> ids);
<TResult> TResult load(Class<TResult> clazz, String id);
Parameter | Type | Description |
---|---|---|
path | String |
Path in documents in which the server should look for 'referenced' documents. |
ids | String |
Ids to load. |
Return Type | Description |
---|---|
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.class, "products/1");
Supplier supplier = session.load(Supplier.class, product.getSupplier()); // this will not make server call
Load - multiple entities
To load multiple entities at once, use one of the following load
overloads.
<TResult> Map<String, TResult> load(Class<TResult> clazz, String... ids);
<TResult> Map<String, TResult> load(Class<TResult> clazz, Collection<String> ids);
Parameters | ||
---|---|---|
ids | Collection |
Multiple document identifiers to load |
Return Value | |
---|---|
Map<String, T> | Instance of Map which maps document identifiers to T or null if a document with given ID doesn't exist. |
Map<String, Employee> employees
= session.load(Employee.class,
"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> T[] loadStartingWith(Class<T> clazz, String idPrefix);
<T> T[] loadStartingWith(Class<T> clazz, String idPrefix, String matches);
<T> T[] loadStartingWith(Class<T> clazz, String idPrefix, String matches, int start);
<T> T[] loadStartingWith(Class<T> clazz, String idPrefix, String matches, int start, int pageSize);
<T> T[] loadStartingWith(Class<T> clazz, String idPrefix, String matches, int start, int pageSize, String exclude);
<T> T[] loadStartingWith(Class<T> clazz, String idPrefix, String matches, int start, int pageSize, String exclude, String startAfter);
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 | |
---|---|
T[] | Array of entities matching given parameters. |
Example I
// return up to 128 entities with Id that starts with 'employees'
Employee[] result = session
.advanced()
.loadStartingWith(Employee.class, "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.class, "employees/", "1*|2*", 0, 128);
ConditionalLoad
The conditionalLoad
method takes a document's change vector.
If the entity is tracked by the session, this method returns the entity. If the entity
is not tracked, it checks if the provided change vector matches the document's
current change vector on the server side. If they match, the entity is not loaded.
If the change vectors do not match, the document is loaded.
In other words, this method can be used to check whether a document has been modified since the last time its change vector was recorded, so that the cost of loading it can be saved if it has not been modified.
The method is accessible from the session.advanced()
operations.
<T> ConditionalLoadResult<T> conditionalLoad(Class<T> clazz, String id, String changeVector);
Parameter | Type | Description |
---|---|---|
clazz | Class<T> |
The class of a document to be loaded. |
id | String |
The identifier of a document to be loaded. |
changeVector | String |
The change vector you want to compare with the server-side change vector. If the change vectors match, the document is not loaded. |
Return Type | Description |
---|---|
ConditionalLoadResult(Class<T>, String ChangeVector) |
If the given change vector and the server side change vector do not match, the method returns the requested entity and its current change vector. If the change vectors match, the method returns default as the entity, and the current change vector.If the specified document, the method returns only default without a change vector. |
Example
try (IDocumentSession session = store.openSession()) {
String changeVector;
User user = new User("Bob");
session.store(User.class, "users/1");
session.saveChanges();
changeVector = session.advanced().getChangeVectorFor(user);
}
User user = new User("Bob");
String changeVector = "a";
try (IDocumentSession session = store.openSession()) {
// New session which does not track our User entity
// The given change vector matches
// the server-side change vector
// Does not load the document
ConditionalLoadResult<User> result1 = session.advanced()
.conditionalLoad(User.class, "users/1", changeVector);
// Modify the document
user.setName("Bob Smith");
session.store(user);
session.saveChanges();
// Change vectors do not match
// Loads the document
ConditionalLoadResult<User> result2 = session.advanced()
.conditionalLoad(User.class, "users/1", changeVector);
}
Stream
Entities can be streamed from the server using one of the following stream
methods from the advanced
session operations.
<T> CloseableIterator<StreamResult<T>> stream(IDocumentQuery<T> query);
<T> CloseableIterator<StreamResult<T>> stream(IDocumentQuery<T> query, Reference<StreamQueryStatistics> streamQueryStats);
<T> CloseableIterator<StreamResult<T>> stream(IRawDocumentQuery<T> query);
<T> CloseableIterator<StreamResult<T>> stream(IRawDocumentQuery<T> query, Reference<StreamQueryStatistics> streamQueryStats);
<T> CloseableIterator<StreamResult<T>> stream(Class<T> clazz, String startsWith);
<T> CloseableIterator<StreamResult<T>> stream(Class<T> clazz, String startsWith, String matches);
<T> CloseableIterator<StreamResult<T>> stream(Class<T> clazz, String startsWith, String matches, int start);
<T> CloseableIterator<StreamResult<T>> stream(Class<T> clazz, String startsWith, String matches, int start, int pageSize);
<T> CloseableIterator<StreamResult<T>> stream(Class<T> clazz, String startsWith, String matches, int start, int pageSize, String startAfter);
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 | Reference streamQueryStats (out parameter) |
Information about the streaming query (amount of results, which index was queried, etc.) |
Return Value | |
---|---|
CloseableIterator<StreamResult |
Iterator 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:
try (CloseableIterator<StreamResult<Employee>> iterator =
session.advanced().stream(Employee.class, "employees/")) {
while (iterator.hasNext()) {
StreamResult<Employee> employee = iterator.next();
}
}
Example 2
Fetch documents for a ID prefix directly into a stream:
ByteArrayOutputStream baos = new ByteArrayOutputStream();
session
.advanced()
.loadStartingWithIntoStream("employees/", baos);
Remarks
Information
Entities loaded using stream
will be transient (not attached to session).
IsLoaded
Use the isLoaded
method from the advanced
session operations
To check if an entity is attached to a session (e.g. because it's been
previously loaded).
isLoaded
checks if an attempt to load a document has been already made
during the current session, and returns true
even if such an attemp was
made and failed.
If, for example, the load
method was used to load employees/3
during
this session and failed because the document has been previously deleted,
isLoaded
will still return true
for employees/3
for the remainder
of the session just because of the attempt to load it.
boolean isLoaded(String id);
Parameters | ||
---|---|---|
id | String |
Entity ID for which the check should be performed. |
Return Value | |
---|---|
boolean | Indicates if an entity with a given ID is loaded. |
Example
boolean isLoaded = session.advanced().isLoaded("employees/1");//false
Employee employee = session.load(Employee.class, "employees/1");
isLoaded = session.advanced().isLoaded("employees/1"); // true