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How to write query with prefix for table name in entity framework

I have WPF app with Oracle DB. I use Entity Framework. Connection string:
DATA SOURCE=localhost:1521/ora;PASSWORD=1;PERSIST SECURITY INFO=True;USER ID=user
I need to connect to new DB with the same namespace, but another USER ID and PASSWORD. I can't create new connection string because USER ID and PASSWORD are unique for each user of the app. I need to run only two queries to new DB. For example
SELECT t.column1, t.column2 FROM "USER ID".tableName t;
What is the best way to do this?
Thanks

You can create a new connection string dynamically at runtime and use this one to connect to the database and run your two queries.
How to: Build an EntityConnection Connection String: https://learn.microsoft.com/en-us/dotnet/framework/data/adonet/ef/how-to-build-an-entityconnection-connection-string
SqlConnectionStringBuilder Class: https://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlconnectionstringbuilder(v=vs.110).aspx

Distributed transaction the same connection

Hi I noticed that if I use two edmx , and each one has it's own connection string, but they point to the same database, and server, user and password is the same, then distributed transaction is created. Is it any way to avoid it ?

You have to tell EF about the single Database connection. You can do it simply by openning the connection yourself after creating the context.
Like this :
using (var ctx = new YourEntities())
{
((IObjectContextAdapter)ctx).ObjectContext.Connection.Open();
//your other code
}

How to create connection string that independent on instance and server name?

i want my application can run on every device that maybe have different server name and instance. my connection string is below:
DBDataContext db = new DBDataContext(#"Data Source=(LocalDB)\v11.0;AttachDbFilename=|DataDirectory|\App_data\DB.mdf;Integrated Security=True;User Instance=False");

If I understand you correctly and the Data Source is always on the local server, why don't you get the ip address of the server with System.Web.HttpContext.Current.Request.ServerVariables["LOCAL_ADDR"];
string myLocalserverIP = System.Web.HttpContext.Current.Request.ServerVariables["LOCAL_ADDR"];
then use that in your Data Source string.

System Data Entity. The underlying provider failed on Open

I am creating 2 projects that have the same database (it's an MDF database). The first one is the map editor, and I use XNA 4 and Web Services to connect to it. The second one is the game itself and uses XNA 3.1 and Entity Data Model to connect database.
When I run the map editor and access the database, it runs properly. Bbut when I run the game and access the database, it shows an error "The underlying provider failed on Open"
I think the connection from the web service is not closed yet. But I don't know where I should close the connection.
Here is my code from the web service:
public Map AddNewMap(string username, string mapName, int sizeX, int sizeY)
{
using (BaseModelDataContext context = new BaseModelDataContext())
{
Map newMap = new Map()
{
Username = username,
Name = mapName,
SizeX = sizeX,
SizeY = sizeY,
Upload_Date = DateTime.Now,
Status = 0
};
context.Maps.InsertOnSubmit(newMap);
context.SubmitChanges(System.Data.Linq.ConflictMode.FailOnFirstConflict);
context.Dispose();
return newMap;
}
}
EDIT:
Here is the entity data model code :
using (MazeEntities ent = new MazeEntities())
{
ent.Connection.Open();
return (from map in ent.Map
select map).ToList<Map>();
}
This code runs properly if I did not use the web service before. If I use the web service first, it shows an error at ent.Connection.Open();
Here is the inner exception:
Cannot open user default database. Login failed.\r\nLogin failed for user 'erkape-PC\erkape'.
Connection string for web service :
connectionString="Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\3DMapDatabase.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True"
Connection string for the game:
"metadata=res:///MazeDataModel.csdl|res:///MazeDataModel.ssdl|res://*/MazeDataModel.msl;provider=System.Data.SqlClient;provider connection string="Data Source=.\SQLEXPRESS;AttachDbFilename=D:\eRKaPe\DropBox\TA\Program\3D_Map_Editor\3DMapEditorServices\App_Data\3DMapDatabase.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True;MultipleActiveResultSets=True"" providerName="System.Data.EntityClient" />

For a quick check, can you try adding the following line after the using:
using (BaseModelDataContext context = new BaseModelDataContext())
{
context.Connection.Open();
OR
context.Database.Connection.Open();
// your code here

Finally I found a way to solve my problem after reading some articles.
The connection from the web service doesn't close automatically after I close the map editor. That is why I can't access my database from the game.
I have to change the connection string from both application, I set the User Instance to False. The game can access the database this way.

Please check the following post
http://th2tran.blogspot.ae/2009/06/underlying-provider-failed-on-open.html
Also please Enable for 32 Bit application in the APplication Pool of that application.
This may resolve.

You are trying to return an object (Map) which is associated with the Context. This object has the context information which can't be returned to the client.
You will need to create your own DataContract (a type having necessary properties) that you want to expose to the client.
Or you can use the POCO implementation As described here

Asp.net MVC2 - Multiple databases

I have a database called
"Config" where I have a table called "Customer"
In the Customer table I hold the login credentials, along with a connection String to the client's database.
Inside of my controller I'm checking to see what customer database i'm querying
String connectionString = "";
if (id == 1)
connectionString = #"Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\Client1.mdf;Integrated Security=True;User Instance=True";
else if (id == 2)
connectionString = #"Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\Client2.mdf;Integrated Security=True;User Instance=True";
using (TestDbaseDataContext db = new TestDbaseDataContext(connectionString))
{
var searchRecords = db.SearchRecords;
return View(searchRecords.ToList());
}
There will be an undetermined number of client's using separate databases, these connection strings will change based on archived status, and other factors. I don't think hard coding these strings in app.config will do what I need.
I have a "Master" database, that holds all of the client's configuration settings, along with the client's database connection string. The mater database is only used to mitigate which client database to search. I store the connection strings in the master database so I can pass that connection string for the logged in customer to query the correct database. It is a requirement to have each client in it's own database
How would you store this connection string so I can pass to my datacontext when needed?
Should it be stored in a session variable, or should I query the Config database Customer table in each controller method?

I've set up a similar "siloed" multi-client application before. This is a good case for a session variable. Each user relates to a client, which has its own database. On login, each user should get a "context" object in Session state containing all necessary identifying data, including database connection string.