I try to sync data via GraphQL from my backend. Therefore I use the artemis package to generate my classes. However I then want to cache the data localy and therefore use the sqfentity_gen package to generate classes to safe my data via sql. I can use a json constructor with each framework to convert the data between.However I want to encapsulate certain functionality since I dont want to just safe changed data localy but sync it to the backend and handle certain errors like merge conflicts or missing network. Therefore I am thinking about wrapping the classes with an other one since I cant change the generated code. Is this a good idea or are there other solutions which work better? Would you use a completly diffrent setup? Glad for any suggestions
Instead of generate and/or re-generate (update) classes which are based on db-tables (I assume), you can use solution from the box, in example, NReco.GraphQL
It allows you set db-schema in the json file and just set db-connection. If you have a lot of tables, you can just generate that json file based on metatable info.
Storing and updating classes, from my point of view is useless.
Related
We are developing a CMS based on JCR/Sling/JSP/Felix/etc.
What I found so far is using Nodes are very straight forward and flexible. But my concern is over time it could become too hard to maintain and manage.
So, is it wise to invest in using a OCM? Would it be just an extra layer of complexity? What's the real benefit in OCM if there's any? Or it's better for us to stick to Nodes instead?
And lastly, is Jackrabbit OCM the best option for us if we are to go down that path?
Thank you.
In my personal experience I can say it severly depends on your situation if OCM is a useful tool for your project or not.
The real problem in using OCM (in my personal experience) is when the definition of a class used in existing persisted data (as objects) in the repository has changed. For example: you found it necessary to change some members and methods of a class to match with functionality changes. By this I mean that the class definition of the persisted data object in the repository no longer matches the definition of actual class. When a persisted data is saved to the jcr repository it is usually saved in a format that java understands in terms of serialization. Which means that when something changes to the definition of the used class, the saved data in the repository can no longer be correctly interpreted by java. This issue tends to lead to complex deployment where you need to convert old persisted data objects to the new definition and save them again in the repository to make sure you can still use "old" but still required persisted data.
What does work (in my opinion) is using a framework that allows to map nodes and node properties to java objects directly (for example by using annotations) and the other way around (persist a java object to the repository as a JCR node where the java member fields are actual node properties). This way you stick to the data representation of jcr (nodes with properties) and can still map them to the members of a java class.
I've used a framework like this in a cms called AEM (of Adobe) before, although I must mention this is in a OSGI context (but the prinicipe still stands). The used framework basically allowed maximum flexibility and persists the java object as a JCR node and the other way around. Because it mapped directly to the jcr definition, code changes in the class and members ment just changing annotations, and old persisted data was still usuable without much effort.
I have a project with an existing database which was initially created for a legacy application. It works fine, but over time quite a few of the tables / fields have been lost or under-utilized, but the historical data MAY be useful someday so they're not going anywhere.
Enter 2012 ('13) and Entity Framework 5, an ORM with built in POCO generation (Nice Add!). So bang.. Get a connection to the Oracle Database, gen. up a context and some POCO's.. suh-weet!! But wait.. my POCO's arent really the POCO's I would like to deal with... There's a bunch of fields which i dont need anymore (not to say I'll NEVER need them, but i can't know for sure), so now i've got these POCO's which are basically bloated table mappers... So what should I do.
I see a few solutions here..
1). I could throw them around and only use the fields that I need.
2). I could get into the Model Surface and start axing the unused fields.
3). "Code-First" approach and tie the objects into the existing DB, it's a large DB though (i'm pretty sure this is possible, right?)
4). Create my own POCO / DTO's in it's own model project and these will essentially become my "domain model", but the mapping back into the context could be painful..
Lastly, do these POCO's / DTO's need to be in their own project?? What is there REALLY to gain.. seeing things like "YAGNI", i feel like it can sit right under the .edmx and never bother anyone..
On a side note, i will be needing a few of these via JSON too, so the whole serializable ability needs to be considered..
Can i just partial class the generated POCO's and only "Attribute" the properties I'll be needing?
anyhow, it'd be great to hear from past experience, or thoughts on the matter..
I could see this being in Programmers, but i figured I'd start it here.
We have a very similar situation, a large legacy DB2 database of which we need small portions of specific tables for our applications.
To do this we used entity framework code first models for the relevant subsections of data we were interested in. This meant we could do a few important things:
remove irrelevant data from the model to make code more discoverable
rename fields inside our model and map them to names that make sense in the app rather than existing column names
reduce the volume of data pulled back by queries (ie our selects dont grab all the extra bits)
where 2 formats of data exist use the modern standard rather than historical format
This works out really well for us, however a couple of things to note:
if you are writing make sure you include all required fields in the model
you can generate you CF classes but you will have to trim them a bit
generating from non mssql can sometimes be more tricky
In terms of json serialisation we do this too however we use a different model for this and use automapper to translate. You should in most cases be able to serialise without needing to add extra attributes but if they are required you can just add them to your pocos alongside any ef attributes.
I know that core data should not be considered as ORM but it still offers the functionality that is similar to ORM. Just curious, is it implementing data mapper pattern? I know "The Data Mapper is a layer of software that separates the in-memory objects from the database. Its responsibility is to transfer data between the two and also to isolate them from each other." (Martin Fowler). IMHO context manager handles all SQL stuff into one transaction, so it's very performance wise design and IMHO core data might be considered implementing data mapper pattern.
One year latter, I will contribute with my two cents
I am not an ORM expert and just recently started something using a Data Mapper, but as a long time Core Data user I can say that no. The main objective of this pattern is having a clear cut of a domain object from all database related operations.
Once I start writing unit tests, the first thing I notice is that I must load a database, even if it is just some in memory store, but I do must load one. Also there are no mappers for each class, I have no control about how each relation is stored.
Core Data loads lots of meta information about your object graph and forces some structure to them. Although you can change the persistent store and bake something of your own, you will have lots of restrictions about how to do it, with a clear "relational" feeling to it.
The idea is good, we might say it is some variation of it. Something that I do love is that the save operation is done by the context, not the object itself. So there is some type of separation.
However look at those functions like "awakeFromFetch" or "didSave", both operations are related with the data store, not a plain domain object. A proper Data Mapper pattern would allow you to define those operations for each persistent store, not unified in a single object.
UPDATE:
Funny enough one day after my answer I had to deal with an old CoreData based project and must come back to improve this answer. To make things clear, I do consider that "seems like a pattern" is not enough. For example, implementation of the facade and adapter patterns is quite similar, but you name them differently depending on how you use them.
Is Core Data implementing data mapper?
I must say that my "not quite" should have been "definitely not!"
I have just been very angry because I needed to rename some fields and later add new ones. Although I do know quite well how auto-migrations work with Core Data I forgot how annoying these are.
How many times do you need some new field, rename something, experiment until you get it right.... and every single tiny change requires a full blown database migration? With Data Mappers this never happens because domain objects are perfectly decoupled. You only touch the database to catch up with the domain objects after you finish some new feature. Core Data forces you to bind at every single moment every single detail of your domain objects.
Boy, how sweet life was until I forgot that "tiny" annoyance of Core Data being the exact opposite of what you can achieve with data mappers.
We are using mongodb with c#. We are trying to figure out a way to keep our collection consistent seamlessly. Right now, if a developer make any changes to the class structure(add a field or change data type or changing the property within a nested class) he/she has to change the mongo collection manually.
Its a pain as our project is growing and the developers working on the project keeps increasing. Was wondering whether someone already have figured out a way to manage this issue.
Research
I found a similar question. however, couldn't find the solution.
Found a way to find all properties Finding the properties; however, datatype and nested documents becomes an issue.
If you want to migrate gradually as records are accessed you need to follow a few simple rules:
1) If you add a field it had better be nullable or have a default value specified.
2) Never rename fields, never change field types
- Instead always add new fields, add migration code, remove the old fields only when all documents have been migrated over.
For prototyping with MongoDB and C# I build a dynamic wrapper ... that lets you specify your objects using only interfaces (no classes needed), and it lets you dynamically add new interfaces to an existing object. Not ready for production use but for prototyping it saves a lot of effort and makes migration really easy.
I've just started learning Google Web Toolkit and finished writing the Stock Watcher tutorial app.
Is my thinking correct that if one wants to persist a business object (like a Stock) using JDO and send it back and forth to/from the client over RPC then one has to create two separate classes for that object: One with the JDO annotations for persisting it on the server and another which is serialisable and used over RPC?
I notice the Stock Watcher has separate classes and I can theorise why:
Otherwise the gwt compiler would try
to generate javascript for everything
the persisted class referenced like
JDO and com.google.blah.users.User, etc
Also there may be logic on the server-side
class which doesn't apply to the client
and vice-versa.
I just want to make sure I'm understanding this correctly. I don't want to have to create two versions of all my business object classes which I want to use over RPC if I don't have to.
The short answer is: you don't need to create duplicate classes.
I recommend that you take a look from the following google groups discussion on the gwt-contributors list:
http://groups.google.com/group/google-web-toolkit-contributors/browse_thread/thread/3c768d8d33bfb1dc/5a38aa812c0ac52b
Here is an interesting excerpt:
If this is all you're interested in, I
described a way to make GAE and
GWT-RPC work together "out of the
box". Just declare your entities as:
#PersistenceCapable(identityType =
IdentityType.APPLICATION, detachable
= "false") public class MyPojo implements Serializable { }
and everything will work, but you'll
have to manually deal with
re-attachment when sending objects
from the client back to the server.
You can use this option, and you will not need a mirror (DTO) class.
You can also try gilead (former hibernate4gwt), which takes care of some details within the problems of serializing enhanced objects.
Your assessment is correct. JDO replaces instances of Collections with their own implementations, in order to sniff when the object graph changes, I suppose. These implementations are not known by the GWT compiler, so it will not be able to serialize them. This happens often for classes that are composed of otherwise GWT compliant types, but with JDO annotations, especially if some of the object properties are Collections.
For a detailed explanation and a workaround, check out this pretty influential essay on the topic: http://timepedia.blogspot.com/2009/04/google-appengine-and-gwt-now-marriage.html
I finally found a solution. Don't change your object at all, but for the listing do it this way:
List<YourCustomObject> secureList=(List<YourCustomObject>)pm.newQuery(query).execute();
return new ArrayList<YourCustomObject>(secureList);
The actual problem is not in Serializing the Object... the problem is to Serialize the Collection class which is implemented by Google and is not allowed to Serialize out.
You do not have to create two versions of the domain model.
Here are two tips:
Use a String encoded key, not the Appengine Key class.
pojo = pm.detachCopy(pojo)
...will remove all the JDO enhancements.
You don't have to create separate instances at all, in fact you're better off not doing it. Your JDO objects should be plain POJOs anyway, and should never contain business logic. That's for your business layer, not your persistent objects themselves.
All you need to do is include the source for the annotations you are using and GWT should compile your class just fine. Also, you want to avoid using libraries that GWT can't compile (like things that use reflection, etc.), but in all the projects I've done this has never been a problem.
I think that a better format to send objects through GWT is through JSON. In this case from the server a JSON string would be sent which would then have to be parsed in the client. The advantage is that the final Javascript which is rendered in the browser has a smaller size. thus causing the page to load faster.
Secondly to send objects through GWT, the objects should be serializable. This may not be the case for all objects
Thirdly GWT has inbuilt functions to handle JSON... so no issues on the client end