I was going through HiveMetastoreBridge code in Apache Atlas and encountered few doubts.Pardon me if these questions are very naive.
HiveMetastoreBridge code
Why are we clearing relationships in findEntity method?
What does add referred entity does exactly in the background ? To be clear in toTableEntity method we are adding ObjectId of related entites as attributes as well calling addReferredEntity method of AtlasEntity.
In registerInstance method why are we creating references from first entity to other referred entities in else if statement. When will multiple entities be created and why will the first have reference to others?
In importTable method why after creating AtlasEntity processInst we are again creating AtlasEntitiesWithExtInfo createTableProcess and adding process entity and path entity to it? Why not Table entity too?
Related
I'm using Symfony2 and Doctrine 2.0. I'm trying to read data from an XML feed and map this to new or existing entities in the database. When data in the XML feed changes I need update existing entities, but when the data is added I should create new entities.
In my entity classes I'm using the following denormalize methods to map the XML data to the entity's properties:
function denormalize(SerializerInterface $serializer, $data, $format = null)
(Defined in Symfony\Component\Serializer\Serializer called inside my Entity classes)
The docs for this method state that "It is important to understand that the denormalize() call should denormalize recursively all child objects of the implementor." and this is what I'm trying to do. However entities should not know about the EntityManager so how do I check, inside the denormalize() method if a related/child entity already exists or not?
Kind regards,
Matthew
It is indeed a bad idea to call the EntityManager in an entity (and, as far as I know, outside a controller).
I've never faced that problem, but if I were you I'd try to denormalize in one of your controllers, or if it really bothers you, in a service that you call in a controller, and to which you give your EntityManager (here again, best do it in the controller itself, or simply send your objects to the service so it can denormalize the xml "into" the objects).
Best would be to write a controller that works no matter the entity given.
Hope that helps!
I think my problem was in my approach and not really my code!!
Originally, each time I found an entity represented in the XML I would check (using the EntityManager) to see if it was new or existing BEFORE denormalizing it. I took this route because there is duplication in the XML and I was worried about creating duplicate entities in the EntityManager. Cheacking to see if an entity already existed meant I could update the existing entity rather than create a duplicate. Now with my new approach every time I find an entity represented in the XML I denormailze it into a new entity. Of course this creates duplication in the EntityManager, just as there is in the XML, but this can be handled later, hopefully..!
So far this is proving to be a better solution, although I am experiencing some issues when trying to merge the duplicate entities in the EntityManager using $em->merge(); and cascade={"persist", "merge"}. I've posted a new question about this here: Doctrine 2.1 - Relation Lost After ManyToMany Cascade Merge - Symfony2
Matthew
I'm using CoreData and was wondering if I could somehow extend my NSManagedObjects to do custom stuff (like deleting files belonging to this instance).
In my case I have a couple of CoreData entities and each entity may have a folder or file path stored in a property. If the entity gets deleted I want this entity to take care of deleting the referenced files on its own.
Such behavior would be particularly helpful in combination with the "Cascade" deletion rule as removing an entity removes all child entities and their files.
If there is no such mechanism I would write a Category for each entity containing a custom deletion method, including cascading behavior for entities that may have children.
What would you do, is there an elegant solution to my problem? Has this been discussed before and I just haven't found it?
Thanks a lot!
Paul
You can do additional cleanup just before an object is deleted by overriding the prepareForDeletion method in your NSManagedObject subclass.
I am new to Core Data modeling, and I am having a hard time understanding how one-to-many relationships work.
I have a parent entity called Task, which can have several instances of Comment entity. I modeled it like this: on Comments, a relationship to Task called task with the Task entity a destination. On Task, a relationship called comments, with Comment as its destination, and both relationships are each others inverse.
Not defining an inverse results in either warnings or error messages. While modeling this way works, I've noticed that once I create a second comment for a given Task, the first is replaced (one-to-one relationship).
What would be the correct way to tell the Core Data Model that this relationship allows many comments in one Task?
Also, since CoreData seems to manage primary keys on its own, how would I create an NSPredicate to retrieve all comments for a given Task?
Thanks for any suggestions!
First of all you need to set the plural option in the Task entity, select it in your .xdatamodeled and select the relationship property of Task entity to comments you should be able to see this
there is a plural option be sure to check that out. You must recreate your NSManagedObject if your using generated classes and also if your using sqlite store you must delete and rebuild so it will not complain about the new schema not being the same with the old one.
To check if you have a one to many relationship your Task entity should have a property called comments which is a class type of NSSet not Comments.
If you want to retrieve all comments for a given task you need to iterate the NSSet(comments) property of that task.
And here goes yet another question on NHibernate.
This one most likely doesn't have a desired answer, but still - let's give it a try.
I'm currently putting all the efforts into mapping a domain model onto the database using NHibernate. This domain model comes from a framework which is heavily obfuscated. (Not that I have worked a lot with obfuscated code before, but this one in most of the places can be translated neither by Reflector, nor by Resharper.)
Everything went more or less fine until I faced an entity with a required many-to-one relationship represented by a property with no setter with obfuscated backed field.
Is it possible to reference this obfuscated field somehow? A very special IPropertyAccessor?
If not, how can I load a fully constructed entity? The only option to inject a related object is by using a constructor that accepts it. But at the time of instantiating of an entity being loaded, neither IInstantiator nor IInterceptor has any data of it apart from the key. Any other extension points that suit my need?
To allow NHibernate to access your field instead of property you can use this in your mappings:
access="field"
I want to programmatically (without Lightweight Migration) create a mapping model between two models that are exactly the same, except one of the entities (there are a bunch of entities) has different attributes. Let's call this entity "Person". And let's say the destination model has
1) added a new attribute called "address"
2) deleted an attribute called "eyeColor"
3) kept (i.e. not done anything with) an attribute called "name"
How would you create an NSMappingModel between these models programmatically? I happen to have some explicit questions that might help me do this by myself:
Q1) Do I have to create NSEntityMapping objects for all of the entities other than "Person", even if they remain unchanged?
Q2) How do I deal with the "address" attribute in "Person", which is a new one being created? Should I create an NSPropertyMapping for that somehow, that turns nothing into something ("address")?
Q3) How do I deal with the "name" attribute in "Person"? Do I have to create an NSPropertyMapping for that, even though it simply stays the same?
Q4) For the NSEntityMapping corresponding to "Person", is not creating any NSPropertyMapping for "eyeColor" a proper way to get it deleted? Or should I create an NSPropertyMapping for "eyeColor"? If yes, how would this object be created, i.e. what would determine that its purpose is to get rid of "eyeColor"?
Thank you in advance, and I apologize not being able to answer these questions myself, as the documenation really has no good example of how to create NSMappingModels programmatically. Note again that I'm not allowed to use Lightweight Migration. I must do this manually.
I've always used the automatic mapping feature of Xcode but it seems to me you can learn a lot from that as well. Make a model of (parts of) the source model, add a version, modify it to reflect the destination model and generate a Mapping Model (menu Design >> Mapping Model). If you then control-click the .xcmappingmodel Xcode has generated for you and tell the Finder to show you the contents of the package, you'll find an XML file inside that lists all the mappings. You can use the xml as a guide to help you recreate the process in code. Good luck.