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Call connection string into another connection string in web.config

I have two connections in the web.config basically they are calling the same database. I want to manage this in a better manner because change in one config also needs to change the second connection string as well.
<add name="DefaultConnection" connectionString="Data Source=.\SQLEXPRESS;persist security info=True;user id=test;password=test123;database=db-AUTH" providerName="System.Data.SqlClient" />
<add name="dbEntities" connectionString="metadata=res://*/InsuranceFinderModel.csdl|res://*/InsuranceFinderModel.ssdl|res://*/InsuranceFinderModel.msl;provider=System.Data.SqlClient;provider connection string="data source=.\SQLEXPRESS;initial catalog=db-AUTH;persist security info=True;user id=test;password=test123;MultipleActiveResultSets=True;App=EntityFramework"" providerName="System.Data.EntityClient" />
My question is, is there any way i can call the connection string into the other connection string.
For example. default connection connection string into db entities something like
<add name="dbEntities" connectionString="metadata=res://*/InsuranceFinderModel.csdl|res://*/InsuranceFinderModel.ssdl|res://*/InsuranceFinderModel.msl;provider=System.Data.SqlClient;provider connection string= DefaultConnection" providerName="System.Data.EntityClient" />
Any suggestions would be appreciated thanks.

You are not obliged to use connection string defined inside app.config(web.config) file for entity connection. You can change entity connection string at runtime. Read this article for that: http://www.c-sharpcorner.com/UploadFile/dacca2/pass-connection-string-in-run-time-to-entity-framework/ .
Also you can get another connnection string and separete every part of connection string( DataBase,DataSource and etc.) using StringConnectionBuilder class https://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlconnectionstringbuilder.initialcatalog.aspx.
The solution is: Get DefaultConnection string and change entity connection at runtime.

Connection string has quotation mark, how to pass it to SqlConnection

I have created a LocalDB database in my project and its connection string is :
Data Source=(LocalDB)\v11.0;AttachDbFilename="E:\Projects\visual studio 2013\Projects\sqlce\mydb.mdf";Integrated Security=True;Connect Timeout=30
How should I pass it to SqlConnection()?
Note that it has an address within quotation marks. Have I done anything wrong?
I guess even if I program it correctly it won't work in another computer which doesn't have that .mdf file in that exact place. Isn't it so?
How can I have a program with a portable database so I can easily publish my pp?

Add the mdf file to your solution and and change the property "Copy to Output Directory" to Copy Always. Don't hardcode the mdf file path in connection string. Add the connection string in app.config or web.config file like below:
<connectionStrings>
<add name="DefaultConnection" connectionString="Data Source=(LocalDb)\v11.0;AttachDbFilename=|DataDirectory|\myDB.mdf;Initial Catalog=MyDatabaseName;Integrated Security=True"
providerName="System.Data.SqlClient" />
</connectionStrings>
Then you can access the connection string in your C# code as below:
string conStr = System.Configuration.ConfigurationManager.ConnectionStrings["DefaultConnection"].ToString()
If you face any error regarding accessing the mdf file, the you can set the DataDirectory in your C# code using AppDomain.CurrentDomain.SetData() method.

<connectionStrings>
<add
name="NorthwindConnectionString"
connectionString="Data Source=serverName;Initial
Catalog=Northwind;Persist Security Info=True;User
ID=userName;Password=password"
providerName="System.Data.SqlClient"
/>
</connectionStrings>
you can access by
connString =rootWebConfig.ConnectionStrings.ConnectionStrings["NorthwindConnectionString"];
More about connection string
SqlConnection con = new SqlConnection(connstring);
or you can go in this way like
SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["NorthwindConnectionString"].ConnectionString);

Dynamics Connection SQL Server C#

I would like some explanations on how to create and set up a dynamic connection to SQL Server DB engine in a C # project

if you want connection string in config and read it than you need to do like this , put possible connectionstring in config
<connectionStrings>
<add name="CharityManagement"
connectionString="Data Source=.;Initial Catalog=CharityManagement;Integrated Security=True"/>
<add name="CharityManagement_two"
connectionString="Data Source=.;Initial Catalog=CharityManagement_two;Integrated Security=True"/>
</connectionStrings>
and than read it base on condition using configurationmanager class
//to read first connection string
var connectionString=ConfigurationManager.ConnectionStrings["CharityManagement"].ConnectionString;
//to read second connection string
var connectionString=ConfigurationManager.ConnectionStrings["CharityManagement_two"].ConnectionString;

This is what you're after
In the config file
<connectionStrings>
<add name="myConnectionString" connectionString="server=localhost;database=myDb;uid=myUser;password=myPass;" />
</connectionStrings>
Then to read the connection string in your code you will do
string connStr = ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;
Don't forget to use using System.Configuration;
Further reading here

How to set a proper connection string for EF DB First?

I have an ArgumentException : Keyword not supported: 'metadata'.
I tried many things, read many posts. I dont know what to do...
This is my CS :
<add name="CDPContext"
connectionString="metadata=res://*/CDP_Model.csdl|
res://*/CDP_Model.ssdl|
res://*/CDP_Model.msl;
provider=System.Data.SqlClient
provider connection string='Data Source=(LocalDb)\v11.0;
AttachDbFilename=\CDP.mdf;
Initial Catalog=CDP;
Integrated Security=True;
MultipleActiveResultSets=True;
App=EntityFramework'"
providerName="System.Data.SqlClient" />
Thanks.

the connection string you provided above is for model first.
to use connection string for code first you could write your connection string as below
<add name="CDPContext" connectionString="Data Source=(LocalDb)\v11.0;
AttachDbFilename=\CDP.mdf;
Initial Catalog=CDP;integrated security=True;MultipleActiveResultSets=True;" providerName="System.Data.SqlClient" />
and also go to you context, if there is a throw exception in it, just remove it.

providerName="System.Data.SqlClient" is the wrong provider for DB First
instead use providerName="System.Data.EntityClient" to access the db using the EDM...

How to solve database initialization error?

I have been testing out different things and have concluded that the following error is the reason my database will not initialize and throws an exception. The exception occurs when I reference the database and initialize it. My Web.config connection string is fine as you can see. I am using Entity Framework 6, MSSQL, and C#. Any help would be appreciated.
Exception:
Cannot open database \"xxx\" requested by the login. The login failed.\r\nLogin failed for user 'xxxx'.
Connection String:
<add name="WebDBContext" connectionString="Data Source=(LocalDb)\v11.0;Initial Catalog=WebDB;Integrated Security=SSPI;" providerName="System.Data.SqlClient"/>
Code:
private SchoolContext db = new SchoolContext();
public ViewMethod Method()
{
var students = from s in db.Students select s; //EXCEPTION IS THROWN HERE
}

You should mention userid and password in connection string
<add name="WebDBContext" connectionString="Data Source=(LocalDb)\v11.0;Initial Catalog=WebDB;Integrated Security=SSPI;User ID=xyz;pwd=top$secret;" providerName="System.Data.SqlClient"/>

Your connection string is not in the format required by EF, it should actually look similiar to this:
<add name="XYZ" connectionString="metadata=res://*/ModEntity.csdl|res://*/ModEntity.ssdl|res://*/ModEntity.msl;provider=System.Data.SqlClient;provider connection string="Data Source=SomeServer;Initial Catalog=SomeCatalog;Persist Security Info=True;User ID=Entity;Password=SomePassword;MultipleActiveResultSets=True"" providerName="System.Data.EntityClient" />

Also use linq query.
var students = db.Students;
<connectionStrings>
<add name="WebDBContext" connectionString="metadata=res://*/Models.ModelName.csdl|res://*/Models.ModelName.ssdl|res://*/Models.ModelName.msl;provider=System.Data.SqlClient;provider connection string="data source=servername;initial catalog=databasename;user id=username;password=password;MultipleActiveResultSets=True;App=EntityFramework"" providerName="System.Data.EntityClient" />
</connectionStrings>
replace the ModelName to your Model and change connections on your db.