Is there any best practice to bind database connection instances to INDY HTTP Server sessions?
I store usual session data in ARequestInfo.Session.Content.Values but this is only for strings. My current approach for database objects is (TDatabaseis just an example class):
Create a TDictionary<String,TDatabase>.
Create TDatabase instances for every session and store references along with the session id in the dictionary.
Access the dictionary enclosed in critical sections within the session processing to be thread safe.
Destroy TDatabase instances when sessions are destroyed.
I suspect that my approach is overhead and there are much more elegant ways to achieve what I want. If this is the case - Tips are very welcome.
The Session.Content property is a TStrings, which can hold strings AND TObject pointers. You don't need a separate TDictionary to map strings to objects, you can store them together in the Content itself.
Alternatively, you can derive a new class from TIdHTTPSession, add your database connection to that class, and then use the TIdHTTPServer.OnCreateSession event to create instances of that class. Then, to access the database connection, simply typecast any TIdHTTPSession object to your class type.
Related
In my program I need to share connection between many struct for updating data in database.
I use rusqlite for my database
and egui for my GUI
Here my source code.
I put a FIXME in the file counter.rs.
I implemented Widget for displaying data easily.
And when I click on a button I would like to perform a SQL UPDATE ... request but I cannot get database connection.
Thank for you help.
I think I found a solution with the singleton DP but I think it's a bad way to do it.
You may want to separate data from interface - create a separate struct for the Counter UI which holds a DB reference and a copy of the Counter data. Then you can straightforwardly construct such a Counter UI object when you instantiate your counter app, passing your DB connection onwards.
I'm creating a design for a Twitter application to practice DDD. My domain model looks like this:
The user and tweet are marked blue to indicate them being a aggregate root. Between the user and the tweet I want a bounded context, each will run in their respective microservice (auth and tweet).
To reference which user has created a tweet, but not run into a self-referencing loop, I have created the UserInfo object. The UserInfo object is created via events when a new user is created. It stores only the information the Tweet microservice will need of the user.
When I create a tweet I only provide the userid and relevant fields to the tweet, with that user id I want to be able to retrieve the UserInfo object, via id reference, to use it in the various child objects, such as Mentions and Poster.
The issue I run into is the persistance, at first glance I thought "Just provide the UserInfo object in the tweet constructor and it's done, all the child aggregates have access to it". But it's a bit harder on the Mention class, since the Mention will contain a dynamic username like so: "#anyuser". To validate if anyuser exists as a UserInfo object I need to query the database. However, I don't know who is mentioned before the tweet's content has been parsed, and that logic resides in the domain model itself and is called as a result of using the tweets constructor. Without this logic, no mentions are extracted so nothing can "yet" be validated.
If I cannot validate it before creating the tweet, because I need the extraction logic, and I cannot use the database repository inside the domain model layer, how can I validate the mentions properly?
Whenever an AR needs to reach out of it's own boundary to gather data there's two main solutions:
You pass in a service to the AR's method which allows it to perform the resolution. The service interface is defined in the domain, but most likely implemented in the infrastructure layer.
e.g. someAr.someMethod(args, someServiceImpl)
Note that if the data is required at construction time you may want to introduce a factory that takes a dependency on the service interface, performs the validation and returns an instance of the AR.
e.g.
tweetFactory = new TweetFactory(new SqlUserInfoLookupService(...));
tweet = tweetFactory.create(...);
You resolve the dependencies in the application layer first, then pass the required data. Note that the application layer could take a dependency onto a domain service in order to perform some reverse resolutions first.
e.g.
If the application layer would like to resolve the UserInfo for all mentions, but can't because it doesn't know how to parse mentions within the text it could always rely on a domain service or value object to perform that task first, then resolve the UserInfo dependencies and provide them to the Tweet AR. Be cautious here not to leak too much logic in the application layer though. If the orchestration logic becomes intertwined with business logic you may want to extract such use case processing logic in a domain service.
Finally, note that any data validated outside the boundary of an AR is always considered stale. The #xyz user could currently exist, but not exist anymore (e.g. deactivated) 1ms after the tweet was sent.
I currently have a C# winform application in which you enter data that is ultimately relational. The amount of data being stored isn't huge. The original version used SQL CE to store the information. However, I found it to be quite slow. Also, I wanted to be able to save application files using my own extension.
I had changed my approach to basically keep my data loaded in-memory using class objects. To save, I simply serialize everything using ProtoBuf and deserialize when opening a file. This approach is lightning fast and changes are never persisted until a user clicks save. However, I find it a little cumbersome to query my hierarchical data. I query data using Linq-To-Objects. I'll have ClassA having a GUID key. I can reference ClassA in ClassB via the GUID. However, I can't really do an easy SQL join-type query to get ClassB properties along with ClassA properties. I get around it by creating a navigation property on ClassB to ClassA that simple returns ClassA via a LINQ query on the GUID. However, this results in a lot of collection scanning.
What options are out there that give me fast, single-user, relational file storage? I would still like to work in-memory where changes aren't persisted until a user uses File|Save. I would also like to be able to continue querying the data using LINQ. I'm looking at SQLite as an option. Are there better options or approaches out there for me?
UPDATE
I was unaware of the AsReference option in the ProtoMember attribute [ProtoMember(5, AsReference = true)]. If I abandon foreign keys in my classes and simply reference the related objects, then it looks like I'm able to serialize and deserialize using ProtoBuf while keeping my object references. Thus, I can easily use Linq-To-Objects to query my objects. I need to stop thinking from the database side of things.
If you have all your objects in some sort of hierarchical structure, you can also store the exact same objects in other structures at an overhead of 4 bytes/object (32bit machines).
Assuming you have a base object like:
public class HierarchyElement
{
public List<HierarchyElement> Children { get; set; }
public HierarchyElement Parent { get; set; }
}
So you have the root element in a local variable, which via the Children property, and the Children property of those first children, etc etc store an unknown number of objects in a hierarchy.
However, while you are building that object, or after deserialising it, you can add a reference to each HierarchyElement to a List (or other flat structure of your choice).
You can then use this flat list to do your Linq queries against.
Hello People of Stackoverflow, I am using a persistent SharedObject for Adobe Media Server to store and share date in real-time for multiple clients. I am using the SyncEvent to dispatch any event that has been updated.
Reading through the documerntation the SyncEvent contains numerous properties. What i want to achieve is to use remote shared object to store a list of people who are online when one client disconnects all the other clients listed will be updated of the disconnection.
Adobe docs unfortunately doesnt provide any examples how to do this.
Would the best approach be to create a changeList array that contains properties of all members then execute a loop?
Or can anyone suggest any other method?
Thanks
The changelist property of the event contains only the properties that got changed. So, if your shared object contains the list of ids, you should be able to get what you achieve.
Note, that the notification is done for the top level properties stored in the shared object. So, what you want would probably look like:
idSo.setProperty("1", true);
while adding. To remove the user, you should use:
idSo.setProperty("1", null);
To reassert, having
idSo.setProperty("ids", <array of ids>)
would send the whole array when it's updated. So, this would be a bad approach
This sync event would be sent to all the connected shared objects.
I have a very basic query. I am using WPF Binding to edit a object which is loaded by a ISession. If somebody edits this object in the form, because of two way binding and a stateful session, whenever I close the session, changes to the object made in the form are stored back in the database. Which is the best way to avoid this?
The methods I know:
Shadow copy the object and use the copied object as the DataContext (the method I am using as of now).
ISession.Clear
Use IStatelessSession.
Is there any way to reset the object to it's original form before closing the ISession?
If you look here: http://nhforge.org/wikis/howtonh/finding-dirty-properties-in-nhibernate.aspx
It is an example of finding dirty properties. NHibernate internally tracks a persistent object's state by way of the EntityEntry object.
This is useful for you, because with a little modification to the method above, you're able to get old values back ... which you can use to reset the properties.
As for closing your session causing the object to be flushed to the database, you can set the session FlushMode to FlushMode.Never. This will mean no database sync occurs until you call Session.Flush().
Alternatively, you can hook into IFlushEntityEventListener to reset the object state. There are a reasonable examples of using the NHibernate event system on google.
See Managing the caches on NHibernate Forge:
When Flush() is subsequently called, the state of that object will be synchronized with the database. If you do not want this synchronization to occur or if you are processing a huge number of objects and need to manage memory efficiently, the Evict() method may be used to remove the object and its collections from the first-level cache.
I think that sounds like what you want.
I would suggest the use of transactions. You just rollbackthe transaction if that is the case? what do you think?