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What's the proper way to include Entity Framework connection string used in WCF service into a self hosting console application?

I'm doing my homework, a WCF service that uses SQL Server with Entity Framework, hosted through a console application, and using a WPF client.
There are 3 different projects, and the host and the service is in the same solution. I've included the Entity Framework connection string in the console hosts' app.config file from the web.config file from the service. This way the server and the host throw an exception when I try to make a query:
System.Data.Entity.Core.EntityException: 'The underlying provider failed on Open.'
The inner exception says:
SqlException: An attempt to attach an auto-named database for file C:\Users\username\source\repos\BlogAppWcf\BlogHost\bin\Debug\BlogDb.mdf failed. A database with the same name exists, or specified file cannot be opened, or it is located on UNC share.
So it basically searches for the .mdf file in it's own project folder, while it's inside the service's App_Data folder.
The original connection string looks like this, I copied this to the host's app.config from the web.config:
connectionString="metadata=res://*/BlogDbEntities.csdl|res://*/BlogDbEntities.ssdl|res://*/BlogDbEntities.msl;
provider=System.Data.SqlClient;
provider connection string="
data source=(LocalDB)\MSSQLLocalDB;
attachdbfilename=|DataDirectory|\BlogDb.mdf;
integrated security=True;
MultipleActiveResultSets=True;App=EntityFramework""
I've tried modifying the AttachDbFilename attribute in the app.config, I gave it an absolute path like this:
attachdbfilename=C:\Users\username\source\repos\BlogAppWcf\BlogAppWcf\App_Data\BlogDb.mdf;
and this way it works like a charm! No more exceptions on queries.
But this isn't the right way to do it, especially because I have to send it to my teacher. I want to give it a relative path, just like this:
attachdbfilename=..\..\..\BlogAppWcf\App_Data\BlogDb.mdf;
but it doesn't work this way.
Has anyone got any suggestions, maybe I'm doing or thinking something completely wrong?

According to your description and the issue you encountered, I think the problem boils down to the fact that the attached database is not properly attached to VS built-in database server instance. For this reason, I think we could configure the EntityFramework with VS built-in database instance string.
Data Source=(localdb)\MSSQLLocalDB;Initial Catalog=MyStore;Integrated
Security=True;Connect
Timeout=30;Encrypt=False;TrustServerCertificate=False;ApplicationIntent=ReadWrite;MultiSubnetFailover=False
And then override the seed method of the DropCreateDatabaseAlways/DropCreateDatabaseIfModelChanges class to provide the seed data.
Feel free to let me know if there is anything I can help with.

Using a SQL Server Database File from a Class Library in C#

So I have a basic 3-tier application:
Data Access
Business Logic
Presentation
My Data Access layer is a class library, and I'm using Entity Framework and a SQL Server Database File
Say my solution is structured as such
MySolution
\MySolution.Data
\MySolution.Data\App_Data\MySolutionDB.mdf
\MySolution.BusinessLogic
\Presentation
The problem I am trying to solve is that I need to get a folder relative path to the database for the connection string because this project will not always be deployed in into the same folder structure, therefore it is imperative that the connection string is created dynamically based on the relative path.
Could someone offer some assistance on this. please?
P.S. I tried this, but it's not working:
string.Format("Data Source=(LocalDB)\v11.0;AttachDbFilename={0}\\MySolutionDB.mdf;Integrated Security=True", AppDomain.CurrentDomain.GetData("DataDirectory"))
EDIT: Getting this error message, which may be unrelated to the issue...
Connection to the database failed. The connection string is configured
with an invalid LocalDB server name. This may have been set in
'global.asax' by a pre-release version of MVC4. The default connection
factory is now set in web.config so the line in 'global.asax' starting
with 'Database.DefaultConnectionFactory = 'should be removed. See
http://go.microsoft.com/fwlink/?LinkId=243166 for details

Thanks to wdosanjos for pointing out my stupid mistake.
string.Format("Data Source=(LocalDB)\v11.0;AttachDbFilename={0}\\MySolutionDB.mdf;Integrated Security=True", AppDomain.CurrentDomain.GetData("DataDirectory"))
I did not escape \v11.0; it should have been \\v11.0;

Firebird 1.5 / Asp net VS 2010 (legacy database .CDB extension)

I have an old system which generated me a database in .CDB extension (i run on Firebird-1.5.6.5026-0-Win32) and i can access this database in IBExpert to query and stuff. But i need to write an application in .NET (VS 2010 4.0 framaework) so i can read this database and access some of the data to insert into a table inside SQLServer.
I tried many things, changed the server version and other things but i now all i get is ''Cannot find fbembed.dll'' exception error while trying to open the connection. My FB server doesnt have this file since he uses the 'fbclient.dll' already.
Any thoughts on how to connect my application to this .CDB database?
(this firebird version is the same that the legacy system is running, so i used the 1.7RC firebird .net provider within this server)
The connection string used is:
<add name="FirebirdConnectionString" connectionString="User=SYSDBA;Password=masterkey;
Database=localhost:C:\temp\BD\E‌​CLECTIC.CDB;DataSource=localhost;Port=3051;
Dialect=3;Charset=NONE;Role=;Connectio‌​n lifetime=15; Pooling=false;
MinPoolSize=0; MaxPoolSize=50; Packet Size=8192; ServerType=1;"
providerName="FirebirdSql.Data.FirebirdClient"/>

Unless you really want to use Firebird embedded (which you don't as you also specify localhost), you should not specify ServerType=1, but either leave it out entirely or set ServerType=0.
As to your other problem you mention in the comments, I suggest you check if this solves it and otherwise create a new question with more information.

Part of my project started using incorrect connection string - how do I fix that?

I have one solution with one project in it. This project is an asp.net mvc web application with xsockets.net websocket server (everything merged inside single project).
Everything was working for a few months, until today. Today I decided to update entity framework and xsockets.net. There were few errors on the way, but I solved almost all of them... almost.
Well, the part of my project that runs websocket server is not using correct connection string. I mean, I can login to my web application, and move around it (so asp.net mvc is using correct connection string), but my websocket server (which is using the same database) cannot gather any data from database, since it's throwing incorrect connection string exception.
And since everything is in the single project, with single web.config file, I don't know what to do next. I don't believe that this is websocket related error, maybe entity framework update has changed something? Anyways, is there any way to explicitly use connection string inside of a class? What else I can do to fix that?

When Entity Framework connects to create the entity objects it also establishes the connection string to that database. This usually isn't a problem since that project is referenced by another program that is overriding the server connection string with their own app config (or web config).
Typically in code when connecting to an instance of Sql Server, you write your code:
using ( MyServer context = new MyServer(myconfig.ConnectionStrings["MyServerName"]))
{
}
If you exclude providing he connection string when creating the instance of your context, you risk catching the default value created when you updated entity framework. So this probably answers both your questions: the why is it changed your connection string. The explicit use is the code example above.

Odbc connection string format, not finding files

This is kind of a 'double' question that might have a single answer.
I'm working with an Odbc Connection with an AS/400, with my connection string as follows:
driver={iSeries Access ODBC Driver}; system={0}; uid={1}; pwd={2}; DefaultLibraries=*USRLIBL;
I'm able to connect to the system fine.
*USRLIBL contains all the necessary libraries from the user (which is of the type 'API only' which has access to all user libraries).
However, when I try to access certain ERP libraries, it says they can't be found, while other ones can.
So as an extremely basic walkthrough:
1. Open Connection - Query File 1 from Library A: OK! - Close Connection
2. Open Connection - Query File 2 from Library A: OK! - Close Connection
3. Open Connection - Query File 1 from Library B: Exception SQL0204 - in UserName type *FILE not found
Ok, so I added in the specific library that the ERP files would be in, making the connection string as follows, just to test the program:
driver={iSeries Access ODBC Driver}; system={0}; uid={1}; pwd={2}; DefaultLibraries=*USRLIBL, LibraryB;
But then I start getting a different problem (another extremely basic walkthrough)
1. Open Connection - Query File 1 from Library A: OK! - Close Connection
2. Open Connection - Query File 2 from Library A: OK! - Close Connection
3. Open Connection - Query File 1 from Library B: OK! - Close Connection
4. Open Connection - Query File 1 from Library A again: Exception SQL0202 - in LibraryB type *FILE not found.
So my question(s) are:
Why doesn't the odbc connectionstring DefaultLibraries=*USRLIBL not return the correct libraries? (Note: I also tested this using an iDB2Connection which in fact works fine... however, the iDB2Connection can not be deployed as it literally crashes the server)
Why does the second walkthrough throw an exception, it just seems to 'skip past' *USRLIBL after reading from LibraryB even once.
Any thoughts?
Begin Edit:
There are actually two users, DEV and PROD
The *USRLIBL gets all the necessary Libraries from the Environment itself, so if when opening the connection, it detects a localhost environment, or anything that's unsecure (plus a few other caveats), it defaults to DEV log in credentials before creating the connection. This is why the system, uid, and pwd are designated as parameters in the connection (and not just stackoverflow I-dont-want-to-give-out-data placeholders)
The *USRLIBL then pulls the necessary libraries from the API user.
To Clarify, the way it's set up does work using the iDB2 Connector, but because of the limitations of our ERP system (we think), using it with an IIS 7 server causes a catastrophic failure, so we're working with the ODBC connector.
End Edit:

You can qualify your table names as library.filename and not have to deal with any library list issues.
For more information:
Client Access ODBC: Default Libraries Setting
ODBC connection string keywords
Excerpts of the relevant parts are:
With SQL naming convention, the operating system does not perform a library list search to locate an unqualified object. If a default collection is defined, the default collection is used to resolve unqualified SQL statements.
...
With the SYS naming convention, the unqualified SQL statements go to the default collection. If there is no default collection, the current library is used. If no current library is specified, the library list is used.
...
Default Collection
A job attribute set by ODBC that determines the library used when processing SQL statements that contain unqualified SQL names. When a default collection is set all unqualified objects except procedures, functions and types must reside in the default collection, regardless of naming convention.
...
How can I get ODBC to search the library list?
As explained above, edit the ODBC data source and set system naming to SYS. The default library must be empty, or on versions older than R510, the default libraries setting must start with a comma so that no default collection is defined (for example, ",MYLIB1, MYLIB2").
Try this connection string to enable system naming and to not set a default library:
driver={iSeries Access ODBC Driver}; system={0}; uid={1}; pwd={2}; naming=1; DefaultLibraries=,*USRLIBL,LibraryB;

If anyone runs into this post and is using the IBM.Data.DB2.iSeries .NET data provider as I am, the key point taken from above was using the naming=1 and not specifying a "Default Collection". I was finally successful when using the following portion in my connection string
LibraryList= MyLibrary1,MyLibrary2,MyLibrary3,MyLibrary4;naming=1;

An alternative is to set up a separate user profile for each environment. Since the *USRLIBL is set by the job description, this would entail setting up a separate job description as well. For example:
user: WEB job desc: WEB library list: CUSTPROD, ITEMPROD, UTILITY
user: WEBTEST job desc: WEBTEST library list: CUSTTEST, ITEMTEST, UTILITY
The C# code does not change except for using the test or production user ID to authenticate.