I need to query a property of Saga Data class to get a list. It is stored on SqlPersistance table [Data] column as a serialized object.
Think about a scenario that my SagaData has a property called UserName, so I want to query every saga related to that user.
In a sloppy way, I can query the column content, get the list and can create Saga objects out of the content, by querying like:
SELECT [Id]
,[Correlation_TaskId]
,[Metadata]
,[Data]
,[PersistenceVersion]
,[SagaTypeVersion]
,[Concurrency]
FROM [myWonderfulDb].[dbo].[MyWonderfulPeristanceTable]
where JSON_VALUE(Data,'$.Username') = 'arthur'
but I am looking for an elegant way to do it by possibly using NserviceBus API's.
There is a SagaFinder implementation described in ParticularSoftware documentation (link: https://docs.particular.net/persistence/sql/saga-finder) but this returns only one object which does not perfectly fit into my scenario.
Here how it is implemented in the documentation:
class SqlServerSagaFinder :
IFindSagas<MySagaData>.Using<MyMessage>
{
public Task<MySagaData> FindBy(MyMessage message, SynchronizedStorageSession session, ReadOnlyContextBag context)
{
return session.GetSagaData<MySagaData>(
context: context,
whereClause: "JSON_VALUE(Data,'$.PropertyPathInJson') = #propertyValue",
appendParameters: (builder, append) =>
{
var parameter = builder();
parameter.ParameterName = "propertyValue";
parameter.Value = message.PropertyValue;
append(parameter);
});
}
}
Any ideas appreciated. Thank you!
We have guidance about querying saga state available at
https://docs.particular.net/nservicebus/sagas/#querying-saga-data
In short, you can query the saga data, there is no out of the box way provided by NServiceBus because we recommend using a different approach instead:
the saga to publish events containing the required data and have handlers that process these events and store the data in one or more read model(s) for querying purposes.
The major points why we don't recommend it is in my viewpoint these two
By exposing the data outside of the safeguards of the business logic in the saga the risk is that the data is not treated as
read-only. Eventually, a component tries to bypass the saga and
directly modify the data.
Querying the data might require additional indexes, resources etc. which need to be managed by the component issuing the query.
Those additional resources can influence saga performance.
The only purpose of the SagaFinder is to find a single instance of a certain saga that correlates with the incoming message. I'm not aware of any framework functionalities to query saga (data) instances.
Related
I am learning a course topic reflection and metadata from nest documentation. They used #setmetadata('roles') but I don't know metadata come from and when they are used?
I don't know metadata come from
First lets explain what metadata generally means.
Metadata in general means data about data. Its a description of the data in more simpler terms (for e.g data about an image). Taking an example from here.
They used #setmetadata('roles').
Nest provides the ability to attach custom data to route handlers through #SetMetadata. Its a way to declaratively define and store data about your controller(endpoint).
#SetMetadata stores the key value pairs. For example,
SetMetadata('IS_PUBLIC_KEY', true)
findAll(#Query() paginationQuery: PaginationQueryDto) {
return this.testService.findAll(paginationQuery);
}
Here I am setting a key IS_PUBLIC_KEY with a value set to true.
In this scenario you are defining a key named role (most probably and it seems it may be missing a value) which will define what certain types or role can access this controller.
When they are used?
You can use it when you want to define the Guards. For instance, I am using the above findAll controller as a public api. In my guard implementation, I check and see if the value of IsPublic is true then allow any consumer to consume the API.
canActivate(
context: ExecutionContext,
): boolean | Promise<boolean> | Observable<boolean> {
const isPublic = this.reflector.get('IS_PUBLIC_KEY', context.getHandler());
if (isPublic) {
return true;
}
}
Hope this answers your question.
https://docs.nestjs.com/fundamentals/execution-context#reflection-and-metadata:
The #SetMetadata() decorator is imported from the #nestjs/common package.
Using Camunda as the tool for orchestration of the microservices. At later time, I find the process_instances_id generated necessary for continuing a particular process by using it in messageEventReceived(). Code as follows:
val processid = getProcessID(key1, key2)
val runtimeService = processengine.getRuntimeService
val subscription = runtimeService.createEventSubscriptionQuery
.eventType("message")
.eventName(eventname)
.processInstanceId(executionid)
.singleResult
runtimeService.messageEventReceived(subscription.getEventName, subscription.getExecutionId)
As of this moment the processid is saved and then retrieved from the database using the getProcessID(...) function when necessary. Is this proper?
Does camunda already have the list of process_ids in its own database? If so, how do I retrieve a particular process instance id just giving composite key(s)? Is that even possible?
It is the common way. You can also use the public api to get the process instance and his id via the process definition key.
See the following example from the documentation:
runtimeService.createProcessInstanceQuery()
.processDefinitionKey("invoice")
.list();
For your given example there is also a simpler way. It is possible to correlate the message via the runtime service.
See this example from the documenation:
runtimeService.createMessageCorrelation("messageName")
.processInstanceBusinessKey("AB-123")
.setVariable("payment_type", "creditCard")
.correlate();
You can use
runtimeService.createProcessInstanceQuery().list();
the query supports fluent criteria for filtering, for example on process_key, variables, businessKey ...
I am trying get a record updated from database with QueryOver.
My code initially creates an entity and saves in database, then the same record is updated on database externally( from other program, manually or the same program running in other machine), and when I call queryOver filtering by the field changed, the query gets the record but without latest changes.
This is my code:
//create the entity and save in database
MyEntity myEntity = CreateDummyEntity();
myEntity.Name = "new_name";
MyService.SaveEntity(myEntity);
// now the entity is updated externally changing the name property with the
// "modified_name" value (for example manually in TOAD, SQL Server,etc..)
//get the entity with QueryOver
var result = NhibernateHelper.Session
.QueryOver<MyEntity>()
.Where(param => param.Name == "modified_name")
.List<T>();
The previous statement gets a collection with only one record(good), BUT with the name property established with the old value instead of "modified_name".
How I can fix this behaviour? First Level cache is disturbing me? The same problem occurs with
CreateCriteria<T>();
The session in my NhibernateHelper is not being closed in any moment due application framework requirements, only are created transactions for each commit associated to a session.Save().
If I open a new session to execute the query evidently I get the latest changes from database, but this approach is not allowed by design requirement.
Also I have checked in the NHibernate SQL output that a select with a WHERE clause is being executed (therefore Nhibernate hits the database) but don´t updates the returned object!!!!
UPDATE
Here's the code in SaveEntity after to call session.Save: A call to Commit method is done
public virtual void Commit()
{
try
{
this.session.Flush();
this.transaction.Commit();
}
catch
{
this.transaction.Rollback();
throw;
}
finally
{
this.transaction = this.session.BeginTransaction();
}
}
The SQL generated by NHibernate for SaveEntity:
NHibernate: INSERT INTO MYCOMPANY.MYENTITY (NAME) VALUES (:p0);:p0 = 'new_name'.
The SQL generated by NHibernate for QueryOver:
NHibernate: SELECT this_.NAME as NAME26_0_
FROM MYCOMPANY.MYENTITY this_
WHERE this_.NAME = :p0;:p0 = 'modified_name' [Type: String (0)].
Queries has been modified due to company confidential policies.
Help very appreciated.
As far as I know, you have several options :
have your Session as a IStatelessSession, by calling sessionFactory.OpenStatelesSession() instead of sessionFactory.OpenSession()
perform Session.Evict(myEntity) after persisting an entity in DB
perform Session.Clear() before your QueryOver
set the CacheMode of your Session to Ignore, Put or Refresh before your QueryOver (never tested that)
I guess the choice will depend on the usage you have of your long running sessions ( which, IMHO, seem to bring more problems than solutions )
Calling session.Save(myEntity) does not cause the changes to be persisted to the DB immediately*. These changes are persisted when session.Flush() is called either by the framework itself or by yourself. More information about flushing and when it is invoked can be found on this question and the nhibernate documentation about flushing.
Also performing a query will not cause the first level cache to be hit. This is because the first level cache only works with Get and Load, i.e. session.Get<MyEntity>(1) would hit the first level cache if MyEntity with an id of 1 had already been previously loaded, whereas session.QueryOver<MyEntity>().Where(x => x.id == 1) would not.
Further information about NHibernate's caching functionality can be found in this post by Ayende Rahien.
In summary you have two options:
Use a transaction within the SaveEntity method, i.e.
using (var transaction = Helper.Session.BeginTransaction())
{
Helper.Session.Save(myEntity);
transaction.Commit();
}
Call session.Flush() within the SaveEntity method, i.e.
Helper.Session.Save(myEntity);
Helper.Session.Flush();
The first option is the best in pretty much all scenarios.
*The only exception I know to this rule is when using Identity as the id generator type.
try changing your last query to:
var result = NhibernateHelper.Session
.QueryOver<MyEntity>()
.CacheMode(CacheMode.Refresh)
.Where(param => param.Name == "modified_name")
if that still doesn't work, try add this after the query:
NhibernateHelper.Session.Refresh(result);
After search and search and think and think.... I´ve found the solution.
The fix: It consist in open a new session, call QueryOver<T>() in this session and the data is succesfully refreshed. If you get child collections not initialized you can call HibernateUtil.Initialize(entity) or sets lazy="false" in your mappings. Take special care about lazy="false" in large collections, because you can get a poor performance. To fix this problem(performance problem loading large collections), set lazy="true" in your collection mappings and call the mentioned method HibernateUtil.Initialize(entity) of the affected collection to get child records from database; for example, you can get all records from a table, and if you need access to all child records of a specific entity, call HibernateUtil.Initialize(collection) only for the interested objects.
Note: as #martin ernst says, the update problem can be a bug in hibernate and my solution is only a temporal fix, and must be solved in hibernate.
People here do not want to call Session.Clear() since it is too strong.
On the other hand, Session.Evict() may seem un-applicable when the objects are not known beforehand.
Actually it is still usable.
You need to first retrieve the cached objects using the query, then call Evict() on them. And then again retrieve fresh objects calling the same query again.
This approach is slightly inefficient in case the object was not cached to begin with - since then there would be actually two "fresh" queries - but there seems to be not much to do about that shortcoming...
By the way, Evict() accepts null argument too without exceptions - this is useful in case the queried object is actually not present in the DB.
var cachedObjects = NhibernateHelper.Session
.QueryOver<MyEntity>()
.Where(param => param.Name == "modified_name")
.List<T>();
foreach (var obj in cachedObjects)
NhibernateHelper.Session.Evict(obj);
var freshObjects = NhibernateHelper.Session
.QueryOver<MyEntity>()
.Where(param => param.Name == "modified_name")
.List<T>()
I'm getting something very similar, and have tried debugging NHibernate.
In my scenario, the session creates an object with a couple children in a related collection (cascade:all), and then calls ISession.Flush().
The records are written into the DB, and the session needs to continue without closing. Meanwhile, another two child records are written into the DB and committed.
Once the original session then attempts to re-load the graph using QueryOver with JoinAlias, the SQL statement generated looks perfectly fine, and the rows are being returned correctly, however the collection that should receive these new children is found to have already been initialized within the session (as it should be), and based on that NH decides for some reason to completely ignore the respective rows.
I think NH makes an invalid assumption here that if the collection is already marked "Initialized" it does not need to be re-loaded from the query.
It would be great if someone more familiar with NHibernate internals could chime in on this.
I am using Raven to persist sagas and I want to implement IFindSagas, I need to find the saga based on 2 properties, SiteId & EmailAddress so ConfigureMapping won't work. The ISagaPersister interface only lets you look up a single saga by a single property.
I have implemented a saga finder like this
public class MySagaFinder : IFindSagas<MySagaData>.Using<ISomeMessage>
{
public ISagaPersister Persister { get; set; }
public MySagaData FindBy(ISomeMessage message)
{
var lookup = string.Format("{0}__{1}", message.SiteId, message.EmailAddress);
return Persister.Get<MySagaData>("SagaLookup", lookup);
}
}
So basically I've added a property on MySagaData called SagaLookup which is a concatenation of SiteId and EmailAddress. I can then look it up by this. This feels like a hack. Is there any way using the saga persister that I can either get a saga back by multiple properties or get a list of sagas back based on one property that I can then filter by the other property?
IMO it is best to look up by a single "key" property because then you don't need to implement a custom persister. Concatenating the site ID and email address may seem like a hack, but if you think of that as defining the ID of that specific saga then it makes sense. The saga data isn't part of your domain model, it is part of the infrastructure which has specific requirements. However, you should consider whether this definition of the saga ID is unique enough. For example, would it ever be possible for two saga's for the same user in the same site ID to execute at the same time?
I'm developing a WCF Data Service with self tracking entities and I want to prevent clients from inserting duplicated content. Whenever they POST data without providing a value for the data key, I have to execute some logic to determine whether that data is already present inside my database or not. I've written a Change interceptor like this:
[ChangeInterceptor("MyEntity")]
public void OnChangeEntity(MyEntity item, UpdateOperations operations){
if (operations == UpdateOperations.Add)
{
// Here I search the database to see if a matching record exists.
// If a record is found, I'd like to use its ID and basically change an insertion
// into an update.
item.EntityID = existingEntityID;
item.MarkAsModified();
}
}
However, this is not working. The existingEntityID is ignored and, as a result, the record is always inserted, never updated. Is it even possible to do? Thanks in advance.
Hooray! I managed to do it.
item.EntityID = existingEntityID;
this.CurrentDataSource.ObjectStateManager.ChangeObjectState(item, EntityState.Modified);
I had to change the object state elsewhere, ie. by calling .ChangeObjectState of the ObjectStateManager, which is a property of the underlying EntityContext. I was mislead by the .MarkAsModified() method which, at this point, I'm not sure what it does.