I'm new to neo4j and to web java programming.
I'm trying to use neo4j in a servlet application and for performance reasons I prefer to java-embed it rather than using the REST APIs.
The question is: ok, if I use REST then there will be a service listening on a certain porta that manages all the database stuff and execute my query and I'm ok, like mysql and other services. But what's the meaning of "embed" it ? where is the database manager? is it all in the jars?
second question. What is the "database path" I'm specifying when I load databases? is it a logical path that the database uses or it is a real path in which db data will be saved?
last one: I'm thinking to put the database creation in init() method so as to load it once per same-prcess-threads and I put the shutdown in destroy() for the same reason. am i doing correctly?
But on the website I've read that no two instances pointing to the same database can exist at same time. But what for two servlets sharing the same database? I start servlet A and it load database DB and then I start B and what happens?
I think if you are new to Neo4j and Java (Web) programming, you should start with the server and graph modeling.
Stick to Cypher and use it via one of the drivers. Eg. the JDBC driver.
After you have acquainted yourself with Neo4j, Cypher your graph data model etc. and only if you run into performance issues you can look into writing an unmanaged server extension for those use-cases.
Related
I am new to PACT and trying to use pact-net for contract testing for a .net microservice. I understand the concept of consumer test which generates a pact file.
There is the concept of a provider state middleware which is responsible for making sure that the provider's state matches the Given() condition in the generated pact.
I am bit confused on the following or how to achieve this:
The provider tests are run against the actual service. So we start the provider service before tests are run. My provider service interacts with a database to store and retrieve records. PACT also mentions that all the dependencies of a service should be stubbed.
So we run the actual provider api that is running against the actual db?
If we running the api against actual db how do we inject the data into the db? Should we be using the provider api's own endpoints to add the Given() data?
If the above is not the correct approach then what is?
All the basic blog articles I have come across do not explain this and usually have examples with no provider states or states that are just some text files on the file system.
Help appreciated.
I'm going to add to Matt's comment, you have three options:
Do your provider test with a connected environment but you will have to do some cleanup manually afterwards and make sure your data is always available in your db or/and the external APIs are always up and running. Simple to write but can be very hard to maintain.
You mock your API calls but call the real database.
You mock all your external dependencies: the API and the DB calls.
For 2) or 3) you will have to have test routes and inject the provider state middleware in your provider test fixture. Then, you can configure provider states to be called to generate in-memory data if solution 3) or add some data-init if you are in solution 2)
You can find an example here: https://github.com/pact-foundation/pact-net/tree/master/Samples/EventApi/Provider.Api.Web.Tests
The provider tests are run against the actual service
Do you mean against a live environment, or the actual service running locally to the unit test (the former is not recommended, because of (2) above).
This is one of the exceptions to that rule. You can choose to use a real DB or an in-memory one - whatever is most convenient. It's common to use docker and tools like that for testing.
In your case, I'd have a specific test-only set of routes that respond to the provider state handler endpoints, that also have access to the repository code and can manipulate state of the system.
I would like to understand an Axon feature.
Currently, we are developing an application using microservice architecture.
We want to store all service events in a central RDBMS database, like for example PostgreSQL.
Is it possible to use such a store?
We have used the below configuration to store events in same domain DB:
#Bean
public AggregateFactory<UserAggregate> userAggregateFactory() {
SpringPrototypeAggregateFactory<UserAggregate> aggregateFactory =
new SpringPrototypeAggregateFactory<>();
aggregateFactory.setPrototypeBeanName("userAggregate");
return aggregateFactory;
}
Now we want to store events in a central Event Store DB, not with domain DB.
Firstly, the AggregateFactory within any Axon application does not define where or how your events are stored at all.
I instead suggest to read the Event Bus & Event Store section of the Axon Framework reference guide on the matter to explain how you can achieve this.
The short answer to your question is by the way yes, you can have a single Event Store backed by a RDBMS, like PostgreSQL, to store all your events in.
Between duplicated instances of a given application it is actually highly recommended to use the same storage location.
As soon as you are going to span different Bounded Context's, I would suggest to define different Event Stores per context though.
Concluding, you are using an old version of Axon Framework.
I would highly recommend to move the at least the latest Axon 3 release, being 3.4.3, but ideally you start using 4.1.2.
Note that there is no active development taking place on Axon 3 any more, hence the suggestion.
I'm trying to refactor an existing project into PureMVC. This is an Adobe AIR desktop app taking advantage of the SQLite library included with AIR and building upon it with a few other libraries:
Paul Robertson's excellent async SQLRunner
promise-as3 implementation of asynchronous promises
websql-js documentation for good measure
I made my current implementation of the database similar to websql-js's promise based SQL access layer and it works pretty well, however I am struggling to see how it can work in PureMVC.
Currently, I have my VOs that will be paired with DAOs (data access objects) for database access. Where I'm stuck is how to track the dbFile and sqlRunner instances across the entire program. The DAOs will need to know about the sqlRunner, or at the very least, the dbFile. Should the sqlRunner be treated as singleton-esque? Or created for every database query?
Finally, how do I expose the dbFile or sqlRunner to the DAOs? In my head right now I see keeping these in a DatabaseProxy that would be exposed to other proxies, and instantiate DAOs when needed. What about a DAO factory pattern?
I'm very new to PureMVC but I really like the structure and separation of roles. Please don't hesitate to tell me if this implementation simply will not work.
Typically in PureMVC you would use a Proxy to fetch remote data and populate the VOs used by your View, so in that respect your proposed architecture sounds fine.
DAOs are not a pattern I've ever seen used in conjunction with PureMVC (which is not to say that nobody does or should). However, if I was setting out to write a crud application in PureMVC, I would probably think in terms of a Proxy (or proxies) to read information from the database, and Commands to write it back.
I use Fluent NHibernate code to create a MySQL database SessionFactory. No config files (just one value for the connection string in configuration - connectionStrings section of configuration file).
The SessionFactory creation code is contained in a Data tier class: SessionFactoryManager, which implements a singleton internal SessionFactory which is used by the Data and Business tiers to get all the sessions via SessionFactoryManager.OpenSession().
Some of my Business tier methods internally call SessionFactoryManager.OpenSession() to create sessions in a way that is transparent to the Presentation layer. So, when calling this methods there is no parameter or return value involving a session (to keep the Presentation layer "session-agnostic" when using those Business tier methods).
My problem comes when I write the integration tests for the Business layer: I would like to make them run on a SQLite in-memory database. I create a SessionFactoryManager which uses Fluent configuration to configure the SQLite database.
But when testing those methods that internally create the session, I can not tell them to use my testing SessionFactory (configured to use SQLite). So the "real" SessionFactory is called, and so the MySql database is used, not the SQLite.
I'm thinking of several possible solutions, but none of them seems right.
I could migrate the NHibernate configuration in Data layer to config files, and make different NHibernate config files for development/production and test environments, but I really would prefer to keep on with Fluent code.
I could also modify my Data layer to use a single configuration value, databaseMode or similar, that sets the database to be used: testing in-memory or the real one. And write some switch(databaseMode) statements like "case inMemory: { ... fluent code for in-memory SQLite... } case standard: { ... fluent code for standard database ... }". I don't like this approach at all, I don't want to modify my Data tier code functionality just for testing purposes.
Notice that I'm not testing Data layer, but Business layer. Not interested in testing NHibernate mappings, Dao or similar functionality. I already have unit tests for that, running OK with SQLite database.
Also, changing database is not a requirement of my application, so I'm not quite interested in implementing significant changes that allow me to dynamically change the DBMS, I only came to this need in order to write the tests.
A significant point: when using in-memory SQLite the database connection must be the same for all new sessions, otherwise the database objects are not available to the new sessions. So when creating a new session with SessionFactory.OpenSession() a parameter "connection" must be provided. But this parameter should not be used with non in-memory database. So the switch(databaseMode) should be used for any single session creation! Another Data layer code change that I don't like at all.
I'm seriously considering giving up and running my tests with the real database, or at least on an empty one, with its objects created and dropped for any test execution. But with this the test execution will surely be slower. Any ideas? Thanks in advance.
Finally my solution was Inversion Of Control: I changed my data tier so I can inject a custom SessionFactoryBuilder class that makes the Fluently.Configure(...) magic.
In my data tier I use the "real" MySqlSessionFactoryBuilder, in my test projects I write TestMySqlFactoryBuilder or TestSQLiteSessionFactoryBuilder classes, or whatever I need.
I still have problems with SQLite feature that requires that the same connection is used for all sessions, and must be passed as a parameter in every ISession.Open() call. By the moment I have not modified my data tier to add that feature, but I would like to do it in the future. Probably by adding to my SessionFactory singleton a static private member to store the connection used to make SchemaExport, and a static private boolean member like PreserveConnection to state that this connection must be stored in that private member and used in every ISession.Open(). And also wrap ISession.Open() and make sure that no session is opened directly.
I have a web service that executes a task that may take hours to finish (asynchronously)
I would like to share the status of that task by all the clients that connects to the server (I'm using a web application for this)
For example, the first client that calls the page http://localhost/process.aspx
will instantiate the web service and it will call a method to start executing the task. A percentage number will be displayed showing the status of completion. I can do this by polling the web service using AJAX.
If there is another client that tries to opens that page, it should get the same percentage information so no new instances of the web service are created.
How is the best way of doing this?
I thought about different solutions but sooner or later I find new problems.
These are some of the possible alternatives:
Create an static object of the Web service.
Create the object in the global.asax file.
Do you guys have any other ideas? I'm not too familiar designing web sites and this is driving me crazy. I would appreciate if you guys could provide some code snippets.
Thanks
The issue is ensuring that the information pertaining to the single instance of a process is stored in exactly one place.
Your initial thinking can be applied, for instance, by using the Application object, but that will break down in a clustered IIS scenario.
I am not posative that a database is the absolute best solution, but I believe it would give you what you want.
If 100 clients try to start the process at the same time, only one can succeed, right? The databases locking facility will help you make that happen.
There's a method (I'm assuming WCF for the web service) that allows you to have exactly one instance of the service run... link
I think this is what you are trying to accomplish.
Assuming I have understood your requirements correctly. Your webservice should not be creating the instance of the “worker” object.
Your webservice request should log to either a database (as the other poster noted) or a messagequeue of somesort. At this point your “worker” processer (probably some type of service) should take over the job as it requires.
Basically you want to break up your application into something like this
| Webservice | ---------- | Datastore |-----------| Worker |
Any further requests regarding the batch should be managed by the webservice querying the datastore.
Remember webservices are NOT DESIGNED TO DO WORK.