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EntityManager by task

Last modified on February 21, 2013 17:25

The following is a summary of the methods available on the EntityManager arranged by task. For a complete list of methods, please see the EntityManager API documentation EntityManager API documentation .


Note: the terms "manager" and "EntityManager" are interchangeable here as they are almost everywhere in DevForce documentation.

Query

The EntityManager members related to querying entities, either from remote data sources or from its entity cache.

Many of the members that can fetch entities from the server come in both synchronous and asynchronous versions. The asynchronous versions can be used on any client EntityManager. The synchronous versions are only available for regular .NET clients and also can be used by custom server methods calling into a server-side EntityManager. You cannot use (or even see) these synchronous methods on an EntityManager used in other client application environments which do not support synchronous communications.

Members that read exclusively from the entity cache are always synchronous and are available to all EntityManagers, including Silverlight, Windows Store and Windows Phone application EntityManagers.

MemberSummary
ExecuteQuerySynchronously executes its IEntityQuery query argument, returning an untyped IEnumerable of entities. 
ExecuteQuery<T> Synchronously executes its strongly typed IEntityQuery<T> query argument, returning an IEnumerable<T> of T-type entities
ExecuteQueryAsyncExecutes asynchronously its IEntityQuery query argument. An untyped IEnumerable of entities is returned in the completed task.
ExecuteQueryAsync<T>  Executes asynchronously its strongly typed IEntityQuery<T> query argument. An IEnumerable<T> of "T" entities is returned in the completed task.
FindEntities<T> Searches the entity cache for entities of type "T" which also have an entitystate that matches one of the flag values in the EntityState argument.
FindEntitiesSearches the entity cache for all entities whose entitystate matches one of the flag values the EntityState argument. Can optionally limit the search to entities of a specified type.
FindEntitySearches the entity cache for an entity with a given EntityKey. By default the search would not return a deleted entity with that key but you can indicate with a boolean flag that you want the entity if it is deleted.
FindEntityGraphSearches the entity cache for the entity "roots" passed as arguments to the method and also returns the entities related to those root entities. The "entity graph" is the combination of a root and its related entities. The extent of the graph is defined by the relationships identified in the EntitySpan argument.
GetNullEntity<T> Get the "null entity" (aka, the "nullo") for the entity type "T" that represents the "entity not found". Reference navigation from an entity-in-cache (e.g., anOrder.Customer) returns the "nullo" rather than null if the entity can't be found.  
GetNullEntityThe untyped variant of GetNullEntity<T>.
GetQuery<T> Returns an EntityQuery<T> that, if executed, would query for all entities of type "T". The statement, manager.GetEntity<Customer>()), returns a query that, if executed, would retrieve all customers in the database. It is typically the foundation query to which the developer adds filter clauses to narrow the search.
RefetchEntitiesRefreshes the entities identified in the method arguments with the most recent data available from the database. 
RefetchEntitiesAsyncThe asynchronous version of RefetchEntities.
TryExecuteQuerySynchronously executes its IEntityQuery query argument, returning an untyped QueryResult containing the retrieved entities and other information about the processed query. 
TryExecuteQuery<T> Synchronously executes its strongly typed IEntityQuery<T> query argument, returning a QueryResult<T> containing the retrieved entities and other information about the processed query. 
TryExecuteQueryAsyncExecutes asynchronously its IEntityQuery query argument. An untyped QueryResult is returned in the completed task.
TryExecuteQueryAsync<T>  Executes asynchronously its strongly typed IEntityQuery<T> query argument. A QueryResult<T> is returned in the completed task.

Some EntityManager members notify subscribers about query activity.

MemberSummary
QueryingA cancellable event raised when the manager is about to process a query. The manager has not yet determined if it will satisfy the query from its entity cache or will have to go to the server for entities. It is raised before Fetching.
OnQuerying The virtual method that a derived EntityManager can override to raise the Querying event.
FetchingA cancellable event raised when the manager, while processing a query, has determined that it must go to the server for entities. It is raised before sending a query to the server. It won't be raised if the manager expects to satisfy the query entirely from its entity cache. Compare to Querying.
OnFetchingThe virtual method that a derived EntityManager can override to raise the Fetching event.
QueriedAn event raised by the manager after it has processed a query request.  The event is raised even if the query was cancelled or failed.  The query may or may not have fetched data from the server. If it did, the event is raised after entities were retrieved successfully and merged into the entity cache. The EventArgs can tell you whether the query involved a trip to the server and, if so, which of the entities retrieved from the server (including related entities) resulted in changes to the entity cache.
OnQueried The virtual method that a derived EntityManager can override to raise the Queried event.

Finally, a few query-control members.

MemberSummary
DefaultQueryStrategyGet and set the QueryStrategy the manager should use if the query itself does not specify a QueryStrategy.
QueryCacheGet the manager's QueryCache, the special cache that remembers previously issued queries. The manager may decide to fulfill a new query request entirely from its entity cache if the manager finds the query in its QueryCache. Adding and removing queries from the QueryCache is largely automatic but you can manipulate it directly once you gain access to it through this property.

Save

The EntityManager members related to saving cached entities with pending changes.

MemberSummary   
DefaultSaveOptions Gets or sets the SaveOptions to be used as a default for any save with unspecified SaveOptions.
HasChanges Get whether the manager's entity cache contains a changed entity. More specifically whether the entitystate of any cached entity is other than Unchanged.
SaveChanges Save synchronously all changed entities in cache. Overloads accept optional parameters such as /SaveOptions.  
SaveChangesAsync Save asynchronously all changed entities in cache. Same overloads as SaveChanges. 
TrySaveChanges Save synchronously all changed entities in cache. Overloads accept optional parameters such as SaveOptions.  The returned SaveResult provides information about success or failure and the entities that were saved. 
TrySaveChangesAsync Save asynchronously all changed entities in cache. Same overloads as SaveChange. The returned SaveResult provides information about success or failure and the entities that were saved. 

Some EntityManager members notify subscribers about save activity.

MemberSummary
Saving  A cancellable event raised when the manager is about to save. The manager provides the handler with a list of entities it intends to save.
OnSaving The virtual method that a derived EntityManager can override to raise the Saving event.
Saved  Raised when the manager has completed save processing.  Will also be raised if the save failed or was cancelled.  The event args provide information about success or failure and the entities that were saved.  
OnSaved The virtual method that a derived EntityManager can override to raise the Saved event.

Finally, a few save-control members for special situations.

MemberSummary
ForceIdFixup Immediately replace the temporary ids of newly-created entities with server-generated permanent ids for entities whose keys are generated by a custom method. The save process performs this "fix-up" automatically but you can force it to happen sooner. 
ForceIdFixupAsync  The asynchronous version of ForceIdFixup.

Access the entity cache

Some EntityManager members yield insights into the manager's entity cache.

MemberSummary 
IsEntityLoaded(key)  Whether an entity with given EntityKey is in the manager's cache.
CacheStateManager Get the manager's CacheStateManager through which you can save and restore a copy of the entity cache in the form of an EntityCacheState.
GetEntityGroup,T>  Get the EntityGroup  inside the cache that holds the cached instances of type "T".
GetEntityGroup The non-generic version of GetEntityGroup<T> takes the entity type as a parameter.
GetEntityGroupsGet an array of all EntityGroups  in the cache. There will be a group for every type the cache has ever seen.  

Many operations move entities into and out of a manager's entity cache automatically. You can manipulate this cache directly using these EntityManager members.

MemberSummary
AddEntitiesAdd entities to the cache as if they were new, Added entities that do not exist in the database and will be inserted if saved.
AddEntityAdd an entity to the cache as if it were a new, Added entity that does not exist in the database and will be inserted if saved.
AttachEntities Attach entities to the cache as if they were pre-existing, Unchanged entities that might have been queried from the database.
AttachEntity Attach an entity to the cache as if it were a pre-existing, Unchanged entity that might have been queried from the database.
Clear Clear the cache, emptying it of all entities. Also clears the QueryCache described in the Query section above.
Cleared Event raised when Clear is called.
RemoveEntities
(entityState, ...) 
 
Remove all entities with the given entitystate, optionally clearing the QueryCache
RemoveEntities
(entities, ...) 
 
Remove the entities in the argument, optionally clearing the QueryCache.
RemoveEntities
(entityType, entityState) 
 
Remove entities of a particular and entitystate, optionally clearing the QueryCache.
RemoveEntity Remove the entity, optionally clearing the QueryCache.
ImportEntities Import shallow copies of the entities into the cache, merging them according to the provided MergeStrategy.

Create, modify and delete

These methods assist the developer in the course of creating, modifying and deleting entities.

MemberSummary
AcceptChangesTreat all entities with pending changes as if they had been saved. They should appear as if they had been freshly retrieved from the database. Added and Modified entities become Unchanged, their current version values overwrite their original version values. Deleted entities are removed from cache, becoming Detached.
RejectChangesRollback all entities with pending changes. They should appear as if they had been freshly retrieved from the database. Deleted and Modified entities become Unchanged, their current version values restored from their original version values. Added entities are removed from cache, becoming Detached.
CreateEntity<T> Create new entity of type "T"; the entity remains detached although the entity retains the inaccessible memory of the manager that created it.
CreateEntityCreate an entity dynamically with this non-geneneric version of CreateEntity.
EntityChanging Cancellable event raised when a cached entity is about to change, e.g., an entity is about to be added, modified, attached, queried, imported, deleted, detached, committed or rolled back.
EntityChanged Event raised when a cached entity has changed, e.g., an entity was added, modified, attached, queried, imported, deleted, deEtached, committed or rolled back.
GenerateIdGenerate a temporary id for a newly created entity that requires custom Id generation; that temp id becomes permanent during save as result of an id fix-up process.

Configure

The EntityManager members with which to configure a new EntityManager and learn about its current configuration. Constructors have been omitted.

A few members you can set or attach to:

MemberSummary
AuthorizedThreadIdGet and set the id of the thread on which this manager can run.  See the topic on thread safety for more information.
EntityManagerCreatedStatic event raised whenever a new EntityManager is created. Useful for tracking and uniformly configuring the managers created in multiple EntityManager scenarios.
EntityServerError Event raised when the EntityServer returns an exception for any reason.
DefaultEntityReferenceStrategy Gets or sets the EntityReferenceStrategy to be used as a default for any navigation properties with an unspecified EntityReferenceStrategy
DefaultQueryStrategy Gets or sets the QueryStrategy to be used as a default for any queries with an unspecified QueryStrategy.
DefaultSaveOptions Gets or sets the SaveOptions to be used as a default for any save with unspecified SaveOptions.
Options Access to the EntityManagerOptions  controlling miscellaneous aspects of the EntityManager's behavior. 
Tag Get and set an arbitrary object. Useful for distinguishing one manager from another in multiple EntityManager scenarios.
VerifierEngineGet and set the DevForce validation engine assigned to this manager. This is the validation engine used by automatic property validation within a cached entity.

Many of the configuration members you can only read:

MemberSummary
CompositionContext Gets the CompositionContext instance that helps determine how MEF will compose some of the components that support this manager, a key part of the DevForce extensibilty story. You establish the manager's CompositionContext when you construct it.
DataSourceExtension Get the string that identifies the data source targeted by this manager. You set the manager's DataSourceExtension when you construct it.
EntityServiceOption The enumeration indicating whether the manager connects to a remote service (n-Tier), a local service (2-tier) or uses the setting from the configuration file.  You establish the manager's EntityServiceOption when you construct it.
IsClient Whether the manager is running on a client or on the server. The valus is usually true - meaning the manager is running on the client - but a number of processes on the server are provided with a server-side EntityManager; the EntityServer interceptor classes and your custom remote service methods are good examples.  The value would be false for these server-side EntityManagers.
MetadataStore Get the application-wide EntityMetadataStore,  the store of metadata about all currently known entity types in the application.
UsesDistributedEntityServiceGet whether this EntityManager communicates with a remote server as it must for a Silverlight, Windows Store or Windows Phone application EntityManager. It is false for 2-tier deployments.

Miscellaneous server calls

The EntityManager is often the application's sole channel for all communications with the server. Most communications concern data.  Security and other kinds of server communications are addressed by the following members.

Connectivity

By default, the EntityManager automatically and immediately tries to connect to the server upon construction. But you may want to connect and disconnect for a variety of reasons with a method listed here:

MemberSummary
Connect Connect to the EntityServer explicitly and synchronously. 
ConnectAsync Connect to the EntityServer explicitly asynchronously. 
Disconnect Disconnect the manager deliberately and continue running offline.
IsConnected Get whether this manager believes it is connected to the server.
ConnectionStateChanged Event raised when the connection state of the manager to the EntityServer changes.

Secure

We devote a full topic to security elsewhere. In brief, all DevForce EntityManager instances must have acquired a local security context before performing most server operations. 

MemberSummary
AuthenticationContext Get or set the security context used by this manager.
IsLoggedIn Get whether this manager is currently authenticated.  

Remote Service Method

The client may call a custom application method on the application server using one of these two Invoke... methods. These methods are untyped, affording the developer the ultimate luxury of sending almost anything as parameters and receiving almost any kind of result. The developer should consider wrapping these commands in a type-safe manner before exposing them to higher level application layers.

MemberSummary
InvokeServerMethod Call a remote server method synchronously, passing in optional service method parameters of any type. The parameters must be both serializable and understood by the server method. InvokeServerMethod returns the object result that was itself returned by the remote server method. The client may cast the result or otherwise interpret it as best it can. 
InvokeServerMethodAsync The asynchronous variant of InvokeServerMethod, available on all .NET clients. 


Created by DevForce on February 22, 2011 18:29

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