How to connect multiple database in a single app?

hi ppl,
Im being asked to provide a application which is database independent.
I need ur ways to approach this issue.
if u have a solution, do drop in here.
Thanks & Regards,
intelnbril

on the paper, the hibernate persistence framework can achieve that.
In the reality its a bit more complicated as your app becomes more complex.
anyway i'd say it is the best solution

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How to add multiple databases for a single frontend

We have a project based on distributed databases and we have to workout on .Net framework.I want to know some information of connecting multiple databases for a single frontend and how can we access them.
If so we have connected 2 databases for a single frontend in future if I want add one more database to it how it will be possible to do it without disturbing the current connectivity.
Please help me in resolving this problem.
Thanks......

hi,
what do you mean by connecting 2 databases? can you explain further?
using entityframework you can connect to different databases
public class CustomerContext : DbContext
public ReportContext()
: base("DefaultConnection")
public DbSet<Customers> Customers { get; set; }
and your connectionstring (config file)
<connectionStrings>
<add name="DefaultConnection" connectionString="Data Source=(LocalDB)\v11.0;AttachDbFilename=D:\\Database\Project.mdf;Integrated Security=True" providerName="System.Data.SqlClient" />
</connectionStrings>
you can add more connection strings on it.
https://msdn.microsoft.com/en-us/library/vstudio/cc716756(v=vs.100).aspx
https://msdn.microsoft.com/en-us/library/ms254978(v=vs.110).aspx
Please remember to mark the replies as answers if they help and unmark them if they provide no help.

How to access multiple database present in single instance

Hi Team,
In oracle 11.2, can there be multiple databases in an instance??? In one of our environment, I could see multiple databases in an instance. Could you please help me in giving the data dictionary or query to access those databases?
Actually, querying v$database, I could see only one database which is same as instance name. But in inventory, there are multiple database in an instance?
I am still not exactly clear about this. Can someone help me with this?
Thanks!
Vidhya

In Oracle one instance manages one (1) database. A database consists of multiple *schemas*.
Other vendors erroneously call a schema 'database'.
So, no, you didn't see multiple databases.
There is also one datadictionary, consisting of a set of views.
All views beginning with dba_ list the entire database, all schemas.
All views beginning with all_ list the objects you have access to.
All views beginning with user_ list your own objects.
The view DICT show you the contents of the datadictionary.
Oracle also has online documentation at http://docs.oracle.com
From your question it is clear you should read the document called the 'Oracle Concepts Manual'.
You can find all documentation for 11gR2 here Oracle Database Online Documentation 11g Release 2 (11.2)
Too many people here don't make any effort to read it. This is probably the reason why you got no response.
Sybrand Bakker
Senior Oracle DBA

How to connect multiple databases

Hi all,
This is my situation , i need to set the max number of connections to one database , if the connection exceeds then i need to connect to another database , is there any way to solve it? please help me

Sounds like you want to write your own load balancer. Sweet!!
As was already stated, this would be best handled by clustering your database servers.
If it's not done at that level, what's the next best option? How are your users currently connecting to the database? Is it through a web server or from stand-alone clients? If it's a web server, the server should have some facility for creating datasources and pooling connections. If you are dead set on switching to a different database when the number of connections in the pool has been maxed out, then you might have to write your own singleton class to manage the connection pool(s).
If your users are connecting through stand-alone clients, you have to force the client applications to connect through a single server that controls the connections.
There's one major problem with switching databases...if a user saves some data there is no guarantee that they will connect to the same database when they want to read the data at some later point. Maybe if there is replication between the two databases in the cluster, they might be able to do that.
Edited by: user9221846 on Feb 11, 2011 8:04 AM
Edited by: user9221846 on Feb 11, 2011 8:05 AM

How can I connect multiple clients to a single client ?

I am currently developing an instant messaging program.I created a server and connected multiple clients to it by using thread logic.However I do not know how to connect multiple client to a single client.
What shall I do for that?Does anybody know a good tutorial or sample program?Or shall anybody explain me what I shall do for building the Instant Messaging part of my chat program?
Thank u in advance.

You may use UDP multicast socket. But since you are using the UDP protocol you might risk losing the data that you send since UDP does not guarantee the safe transfer of data.
Alternately, you might create a server that allows multiple client to connect to it whose connection Socket objects are then stored in a Vector <Socket> object. The server then sends back data to the connected client about the other clients connected to it. Now when the client wants to send data (like an IM) to another connected client, it has to send a request to the server specifying the client login name and the server in turn streams that particular client's Address and Port to the requesting client. The requesting client then initiates the connection with the other client and then starts a conversation. One more thing, when the client communicates it needs to send information to the server like the name by which it likes to be referenced. In this scenario the server acts like a central repository for clients to query the existence of other clients in the chat room. Each client here runs a thread that listens to incoming connections and when a connection is established, may be opens a IM window or something.
The third option is to make the server to relay the information from one client to another. Like say, I'm connected to whoopy server and i want to send "Hello" to jackson, then i send the message (ie, Hello) along with the name of the client to which i wish to send it to (ie, jackson). The server then performs a lookup in its Vector <Socket> object and then initiates a connection with jackson and sends the information. However, this method is pretty costly in that you will be wasting a lot of processing behind the server.
--Subhankar
P.s. If you stumble upon any other brilliant ideas let me know.

How to configure multiple databases in single listener

Hi,
I want to configure upto 8 standby databases in a server. But I do not know how to configure multiple databases within the listener.
Also can I use the same port number for all the databases.
please give your suggestions.
thankyou
satyanag

Please check (http://download.oracle.com/docs/cd/B10501_01/network.920/a96580/toc.htm)
Jonathan Ferreira
http://oracle4dbas.blogspot.com

How to connect to database

Hi Experts,
i am using oracle 10g (10.2),linux4.6 .my databae server contain multiple databases how can connect one database to another database and how can i put this all environment variable in single parameter file

tmadugula wrote:
Hi Experts,
i am using oracle 10g (10.2),linux4.6 .my databae server contain multiple databases how can connect one database to another database and how can i put this all environment variable in single parameter fileYou can see from the responses two very different sets of advice. To know what applies to your situation, you need to clarify what you need to do.
If you are talking about choosing which database you connect to from sqlplus, follow the advice about changing the environment variable ORACLE_SID.
If you are talking about having one database being able to access another (one db acts as the client to another) follow the advice about db links.

JDBC - Connecting Multiple Databases

Hi JDBC's
I would like to know if it is possible to retrive a data from different tables and from different databases using a single query, which mean can I retrive data from multiple tables multiple databases in a single JDBC connection?
If not, How do I implement it?
Any Ideas or please point me to any related solution if you have.
Thanks.

Although theoretically possible in fact a single JDBC connection cannot work with several databases. To implement this feature somebody has to write another aggregating JDBC driver which parse SQL statement and work with other databases in background. I like this idea, but currently there is no such driver available.
Scriptella ETL (http://scriptella.javaforge.com) offers an interesting solutions for cross-database operations. See example on how -to copy a table from oracle to hsqldb: http://snippets.dzone.com/posts/show/3511
If you want to join 2 tables from different databases and copy the result to a third database use the following code:
<query connection-id="db1">
SELECT * FROM Table1
<query connection-id="db2">
SELECT * FROM Table2 WHERE Table2_ID=?Table1_ID
<script connection-id="db3">
INSERT INTO Table3 VALUES (?rownum, ?Table1_Field, ?Table2_Field);
</script>
</query>
</query>
Message was edited by:
ejboy

Multiple databases in a single query

I need to query multiple databases in a single query.
e.g.
Database d1 contains table t1 with column id
Database d2 contains table t2 with column id
I need a query like
SELECT * FROM t1, t2 WHERE t1.id = t2.id;
is this possible in jdbc? if yes can anyone help with some sample code?
thanks,
Ashish Saraf

It is not possible using the JDBC API to query tables in two or more databases using a single query. The reason is that a JDBC Connection is made to a single data source.
However, some databases support the idea of federations or linked tables. What you do is inside the database manager link or federate a table that is present in another DBMS. Then, pose a single JDBC query to the one DBMS which will have its own table and links to the external tables.
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As part of my research program, we have released a shareware version of the UnityJDBC driver that can query multiple databases using a single SQL query. For more information, see:
http://www.unityjdbc.com
http://www.cs.uiowa.edu/~rlawrenc/research/projects.html
Sincerely,
Dr. Ramon Lawrence
Assistant Professor
Department of Computer Science
University of Iowa
[email protected]

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How to connect one database in two threads?

Dear All,
If anyone can tell me how to connect one database concurrently?
I tried the following idea:
1.create a Hashtable to keep database objects(those databases have been opened)
2.Before openning(connecting) a database:first step is to check the hashtable.
If the the database object is in the hashtable, this object will be returned.
If the datatbase object is not in the hastable, open the database and store this opened database object into the hashtable.
I failed the test of this implementation. My test is:Create two threads (extend java Thread class).In each of these two threads, try to open the same database.Just like the following:
MyThread thread1 = new MyThread();
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thread1.start();
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Lu

um not sure i follow exactly but in your code add the word synchronise to it and this means only 1 tread can access it at any 1 time.
So your could have a class which is a singleton so it only opens the dbase once and then all other access share your connection.
so
public class foo{
foo INSTANCE = new foo();
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then all your methods use foo's internal dbase connection. Am i making sense

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Hi
How to connect sybase database in JDeveloper 11g using JConnect? Please help.

User,
It would help if you explained Sybase Jconnect instead of leaving us to google.
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How to connect multiple database in a single app?

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