Session : Loading entities

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

T Load<T>(string id);

T Load<T>(ValueType id);

TResult Load<TResult>(
	string id,
	string transformer,
	Action<ILoadConfiguration> configure);

TResult Load<TResult>(
	string id,
	Type transformerType,
	Action<ILoadConfiguration> configure = null);

TResult Load<TTransformer, TResult>(
	string id,
	Action<ILoadConfiguration> configure = null)
	where TTransformer : AbstractTransformerCreationTask, new();

Parameters
id	string or ValueType	Identifier of a document that will be loaded.
transformer or transformerType	string or Type	Name or type of a transformer to use on a loaded document.
configure	Action	Additional configuration that should be used during operation e.g. transformer parameters can be added.

Return Value
TResult	Instance of TResult or null if document with given Id does not exist.

Example I

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

Example II

// loading 'employees/1'
// and transforming result using 'Employees_NoLastName' transformer
// which returns 'LastName' as 'null'
Employee employee = session.Load<Employees_NoLastName, Employee>("employees/1");

Non string identifiers

The above examples show how to load a document by its string key. What if a type of your entity's identifier is not a string? You need to use an overload of the Load method that takes a parameter which type is ValueType.

Example III

If you have an entity where an identifier is an integer number:

public class EntityWithIntegerId
		{
c int Id { get; set; }
			/*
			...
			*/
		}

you can load it by specifying an integer value as the identifier:

EntityWithIntegerId entity = session.Load<EntityWithIntegerId>(1);

Converting to string identifier

Even if the identifier is a string, you can use the Load<T>(ValueType) overload. The client is aware of the ID generation conventions (collectionName/number), so you could load the entity with key employees/1 by using the code:

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

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

ILoaderWithInclude<object> Include(string path);

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

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

Parameters
path	string or Expression	Path in documents in which server should look for a 'referenced' documents.

Return Value
ILoaderWithInclude	Include method by itself does not materialize any requests, but returns loader containing methods such as Load.

Example I

// 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

Example II

// 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 III

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

Supplier supplier = session.Load<Supplier>(product.Supplier); // this will not make server call

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

TResult[] Load<TResult>(IEnumerable<string> ids);

TResult[] Load<TResult>(IEnumerable<ValueType> ids);

TResult[] Load<TResult>(params ValueType[] ids);

TResult[] Load<TResult>(
	IEnumerable<string> ids,
	string transformer,
	Action<ILoadConfiguration> configure = null);

TResult[] Load<TResult>(
	IEnumerable<string> ids,
	Type transformerType,
	Action<ILoadConfiguration> configure = null);

TResult[] Load<TTransformer, TResult>(
	IEnumerable<string> ids,
	Action<ILoadConfiguration> configure = null)
	where TTransformer : AbstractTransformerCreationTask, new();

Parameters
ids	IEnumerable or IEnumerable or ValueType[]	Enumerable or array of Ids that should be loaded.
transformer or transformerType	string or Type	Name or type of a transformer to use on a loaded documents.
configure	Action	Additional configuration that should be used during operation e.g. transformer parameters can be added.

Return Value
TResult[]	Array of entities in the exact same order as given ids. If document does not exist, value at the appropriate position in array will be null.

Example I

Employee[] employees = session.Load<Employee>(new List<string> { "employees/1", "employees/2" });
Employee employee1 = employees[0];
Employee employee2 = employees[1];

Example II

// loading 'employees/1' and 'employees/2'
// and transforming results using 'Employees_NoLastName' transformer
// which returns 'LastName' as 'null'
Employee[] employees = session
	.Load<Employees_NoLastName, Employee>(new List<string> { "employees/1", "employees/2" });
Employee employee1 = employees[0];
Employee employee2 = employees[1];

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

TResult[] LoadStartingWith<TResult>(
	string keyPrefix,
	string matches = null,
	int start = 0,
	int pageSize = 25,
	string exclude = null,
	RavenPagingInformation pagingInformation = null,
	string skipAfter = null);

TResult[] LoadStartingWith<TTransformer, TResult>(
	string keyPrefix,
	string matches = null,
	int start = 0,
	int pageSize = 25,
	string exclude = null,
	RavenPagingInformation pagingInformation = null,
	Action<ILoadConfiguration> configure = null,
	string skipAfter = null);

Parameters
keyPrefix	string	prefix for which documents should be returned
matches	string	pipe ('|') separated values for which document keys (after 'keyPrefix') 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
pagingInformation	RavenPagingInformation	used to perform rapid pagination on server side
exclude	string	pipe ('|') separated values for which document keys (after 'keyPrefix') should not be matched ('?' any single character, '*' any characters)
configure	Action	Additional configuration that should be used during operation e.g. transformer parameters can be added.
skipAfter	string	skip document fetching until given key is found and return documents after that key (default: null)

Return Value
TResult[]	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>("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);

Example III

// return up to 128 entities with Id that starts with 'employees/' 
// and rest of the Id have length of 3, begins and ends with "1" 
// and contains any character at 2nd position e.g. employees/101, employees/1B1
// and transform results using 'Employees_NoLastName' transformer
Employee[] result = session
	.Advanced
	.LoadStartingWith<Employees_NoLastName, Employee>("employees/", "1?1", 0, 128);

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

IEnumerator<StreamResult<T>> Stream<T>(
    Etag fromEtag, 
    int start = 0, 
    int pageSize = int.MaxValue, 
    RavenPagingInformation pagingInformation = null, 
    string transformer = null, 
    Dictionary<string, RavenJToken> transformerParameters = null);

IEnumerator<StreamResult<T>> Stream<T>(
    string startsWith, 
    string matches = null, 
    int start = 0, 
    int pageSize = int.MaxValue, 
    RavenPagingInformation pagingInformation = null, 
    string skipAfter = null, 
    string transformer = null, 
    Dictionary<string, RavenJToken> transformerParameters = null);

Parameters
fromEtag	Etag	ETag of a document from which stream should start (mutually exclusive with 'startsWith')
startsWith	string	prefix for which documents should be streamed (mutually exclusive with 'fromEtag')
matches	string	pipe ('|') separated values for which document keys (after 'keyPrefix') 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
pagingInformation	RavenPagingInformation	used to perform rapid pagination on server side
skipAfter	string	skip document fetching until given key is found and return documents after that key (default: null)
transformer	String	name of transformer (default: null)
transformerParameters	Dictionary<string, RavenJToken>	parameters to pass to the transformer (default: null)

Return Value
IEnumerator<StreamResult>	Enumerator with entities.

Example I

IEnumerator<StreamResult<Employee>> enumerator = session.Advanced.Stream<Employee>("employees/");
while (enumerator.MoveNext())
{
	StreamResult<Employee> employee = enumerator.Current;
}

Example 2

Using the following transformer:

public class SimpleTransformer : AbstractTransformerCreationTask
{
    public class Result
    {
        public string Name { get; set; }
    }

    public override TransformerDefinition CreateTransformerDefinition(bool prettify = true)
    {
        return new TransformerDefinition
        {
            Name = "SimpleTransformer",
            TransformResults = "from r in results select new { Name = Parameter(\"Name\") }"
        };
    }
}

StreamDocs using the SimpleTransformer defined above and one supplied parameter:

var transformer = new SimpleTransformer();
transformer.Execute(store);

using (IEnumerator<StreamResult<SimpleTransformer.Result>> enumerator = session.Advanced.Stream<SimpleTransformer.Result>("people/", transformer: transformer.TransformerName, transformerParameters: new Dictionary<string, RavenJToken> { { "Name", "Bill" } }))
{
    while (enumerator.MoveNext())
    {
        StreamResult<SimpleTransformer.Result> result = enumerator.Current;
        string name = result.Document.Name;
        Assert.Equal("Bill", name); // Should be true
    }
}

Remarks

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

bool IsLoaded(string id);

Parameters
id	string	Entity Id for which check should be performed.

Return Value
bool	Indicates if entity with 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