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Re: Using database objects in different schemas
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Re: Using database objects in different schemas


  • Subject: Re: Using database objects in different schemas
  • From: André Rothe <email@hidden>
  • Date: Wed, 13 Dec 2017 08:10:20 +0100

Hello Jean,

The problem with the "slave" accounts is, that I don't have the passwords for them. So I cannot create a connection to every account except the "master" account.

Within the "master" there is a table, which holds the account names of the "slaves". So it is possible to get the account names and build within the database some queries like:

sql := 'select * from' || get_a_slave_name() || '.table1';
execute_immediate sql;

But I need such a thing within WebObjects. I looked around in the API and I found a theoretical solution, which I will try today.

* get the "master" model (EOModel), it has a valid database connection
* get the database context of that model
* from the database context get:
  dc.availableChannel().adaptorChannel()

* there is a method describeModelWithTableNames(tablenames), which
  creates an EOModel from the given tablenames

Maybe it is possible, to set full-qualified tablenames there, so I could build EOModels for every "slave" dynamically. The names of the "slaves" I can get from my "master" account with a simple query (this table will be filled by another application). Also I could rename the models, to get better access from the defaultModelGroup (maybe the name of the "slave" account per model).

The questions would be, whether or not the method above will accept full-qualified table names, and whether or not the method is not an abstract method for the Oracle database plugin.

Best regards
André

Am 2017-12-13 00:40, schrieb Jean-François Veillette:
Hmmm … reading your email a few times again, it seems that I didn’t
understand your problem at first and that my answer was off-topic.
I’m still not sure I really understand enough to be of any help, but
let me try again with (I hope) a better answer.

It seems that you would need a new jdbc connection to access the slave DB.
As described in my previous email, you could create a new EOF stack,
listen for the notification to update the model’s connection
dictionary, adjust it to connect to the desired slave DB, then use the
stack at will.

In hope that this is at least a closer attempts to answer your question,

jfv

On Dec 12, 2017, at 10:49 AM, Jean-François Veillette <email@hidden> wrote:

You might need to create a new jdbc connection for every user.
If I understand your situation correctly, I would try to use a unique EOF stack for every session (user). In practice this can work well as long as you don’t have too many sessions (exhausting DB connection). You will have to change the ‘delegate’ that updates the connection dictionary so that it updates it specifically for the current user.

This might sound more complicated than it really is, here is the 2 things you have to do (in short):
1- make sure you create a new EOF stack for every user:
2- Make sure the connection dictionary is correctly set for every new stack

Now in Detail:
1-  make sure you create a new EOF stack for every user:
I would user the pattern of a ‘Provider' to assist me in doing so:
- create an editing context provider that will be responsible for giving you EOEditingContext instances (let’s name it: ECProvider) - have provider to require arguments like the current user’s id, or whatever you need to be able to set the correct connection dictionary. - give editing context from a new EOObjectStoreCoordinator (new/specific EOF stack).

2- Make sure the connection dictionary is correctly set for every new stack
Improve with the provider created in step 1
- the new stack will trigger the initialization of the database connection dictionary (by way of NSNotification), the object responding to that notification should be able to adjust the connection dictionary according to the ‘current user’. You want to update the connection dictionary here, as part of the notification dispatch. ps: Set a breakpoint on ‘ERXModelGroup.resetConnectionDictionaryInModel’ to better understand the mechanism (this is the default method that will update the database connection dictionary when a model is loaded in memory). ps: you can add yourself to receive such notification by “ NSNotificationCenter.defaultCenter().addObserver(this, aSelector, EOModelGroup.ModelAddedNotification, null);” Note that If many objects receive notification, the order is not predictable, so only one should be responsible for updating the connection dictionary.

ps: keep a cache of existing connection based on those users to avoid opening too many connections to the DB as this will most likely be a problem. ps: find a way to close those connections when they are no longer needed (when session dies)

Every time you need a new EOEditingContext, ask ECProvider for it.
If you use session default EC, set it from this provider, just so that you can simply use session.defaultEditingContext later.


I’ve never done this, but this is what I would try to achieve it.
Hope this help,

jfv



On Dec 12, 2017, at 5:59 AM, André Rothe <email@hidden> wrote:

Hi,

I use an Oracle database, which has a "master" schema/account. This aacount uses my Webobjects application. There are a lot of "slave" schemas/accounts, which grant privileges on their own objects (tables, views etc.) to the master. So the master can access these objects like:

select * from slave1.table1;
select * from slave2.table1;

The objects within the "slave" accounts are identical, so it could be possible to use one EO model for all slaves.

How can I access these objects, if the master don't know the user/password for every slave? I cannot change the credentials for the model within the application without the passwords, but I have to change the source of each object within a model to the specific slave before I execute any query. Or should I use rawSQL?

I have no idea, how I could solve this with WebObjects. Is it possible at all?

Best regards
André

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  • Follow-Ups:
    • Re: Using database objects in different schemas
      • From: Markus Ruggiero <email@hidden>
References: 
 >Using database objects in different schemas (From: André Rothe <email@hidden>)
 >Re: Using database objects in different schemas (From: Jean-François Veillette <email@hidden>)
 >Re: Using database objects in different schemas (From: Jean-François Veillette <email@hidden>)

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