Develop Reference

How to access connection string & connect to database

So I'm working on a project involving an external API and a database. This API uses an API specific project type called an Add In and is compiled as a library, then added to the API's source program. This way, I can create self-created 'actions' within in the Add in for the program and call them remotely from a MVC web project. This action contains code also related to updating a database uploaded on a server. When I tried to call this action remotely, I would get this error within the application the add in was added to:
A network-related or instance-specific error occurred while establishing a connection to SQL server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)
I've gotten help with my mentor and troubleshooted the connection string inside the Add Ins app.config. It's verified to be correct (I can access the database directly from the web MVC project). I tried reading the connection string using var connectionString = ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString; in the project, and it just can't be found. When the action is called I get a null object reference error.
Here's my app config for the Add In:
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<connectionStrings>
<add name="DefaultConnection" connectionString="Data Source=PROD4W\PROD4W;Initial Catalog=EplanInterfaceDb;user id = SomeID; password=SomePassword;Integrated Security=False" providerName="System.Data.SqlClient"/>
</connectionStrings>
</configuration>
Here's my code related to the database inside my add In project:
//Here is where my mentor tried to pull the connection string from the //app.config.This is where the object reference error
var connectionString = ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;
//Output the connection string to the screen on outside app
new Decider().Decide(EnumDecisionType.eOkDecision, "Connection: " + connectionString, "", EnumDecisionReturn.eOK, EnumDecisionReturn.eOK);
//Access the database and add a test
using (var context = new DataContext())
{
//Throws network related error mentioned above
context.Macros.Add(new Macro { Name = "test" });
context.SaveChanges();
//Output to the screen if the savechanges was successful
new Decider().Decide(EnumDecisionType.eOkDecision, "Save Changes Called ", "", EnumDecisionReturn.eOK, EnumDecisionReturn.eOK);
}

Using what Mason recommended below you can simply hard code your connection string instead of pulling it from the app.config if it is giving you issues.. Here is an example:
var connectionString = "Hard code connection string";
//Make sure your DataContext has a constructor that takes in a connection string
using (var context = new DataContext(connectionString))
{
context.Macros.Add(new Macro { Name = "test" });
context.SaveChanges();
//Output to the screen if the savechanges was successful
new Decider().Decide(EnumDecisionType.eOkDecision, "Save Changes Called ", "", EnumDecisionReturn.eOK, EnumDecisionReturn.eOK);
}

Entity Framework: The context is being used in Code First mode with code that was generated from an EDMX file

I am developing an WPF application with EF 6 database first approach, I am have 1 project in my solutions, if i run my project this error always appear.
The context is being used in Code First mode with code that was generated from an EDMX file for either Database First or Model First development. This will not work correctly. To fix this problem do not remove the line of code that throws this exception. If you wish to use Database First or Model First, then make sure that the Entity Framework connection string is included in the app.config or web.config of the start-up project. If you are creating your own DbConnection, then make sure that it is an EntityConnection and not some other type of DbConnection, and that you pass it to one of the base DbContext constructors that take a DbConnection. To learn more about Code First, Database First, and Model First see the Entity Framework documentation here: http://go.microsoft.com/fwlink/?LinkId=394715

My mistake was using standard connection string in constructor
(Server = test\test; Database = DB; User Id = test_user;Password = test),
but Entity Framework needs different format
(metadata=res://*/DBModel.csdl|res://*/DBModel.ssdl|res://*/DBModel.msl;provider=System.Data.SqlClient;provider connection string="data source=test\test;initial catalog=DB;integrated security=True;MultipleActiveResultSets=True;App=EntityFramework""" providerName = ""System.Data.EntityClient)
Edit: Changed code to be formatted as code so it's easier to read.

EF makes assumptions based on the presence or absence of a metadata section in the connection string. If you receive this error you can add the metadata section to the connection string in your config file.
E.g. if your connection string looks like this:
<add name="MyModel" connectionString="data source=SERVER\INSTANCE;initial catalog=MyModel;integrated security=True;MultipleActiveResultSets=True;App=EntityFramework" providerName="System.Data.SqlClient" />
Prepend metadata=res://*/MyModel.csdl|res://*/MyModel.ssdl|res://*/MyModel.msl; so that it looks like this:
<add name="MyModel" connectionString="metadata=res://*/MyModel.csdl|res://*/MyModel.ssdl|res://*/MyModel.msl;data source=SERVER\INSTANCE;initial catalog=MyModel;integrated security=True;MultipleActiveResultSets=True;App=EntityFramework" providerName="System.Data.SqlClient" />

One thing you can do is... (if is Database first)
Open the .edmx[Diagram] -> right click -> "Update Model from database"
And see if the will appear the "Add", "Refresh" and "Delete" tabs.
If doesn't... probably your connection is broken and the dialog for VS creates a new connection string will appear instead. =)

You shouldnt use generated connection string, now you have all metadata files included in your solution. Instead try use in connection string section of app.config:
"data source=localhost\sqlexpress; initial catalog=sample; integrated security=True;MultipleActiveResultSets=True;"

None of the above solutions worked for me. But I did find the SqlConnectionBuilder class here which did work: https://learn.microsoft.com/en-us/dotnet/api/system.data.entityclient.entityconnectionstringbuilder?view=netframework-4.8
Its the same as specifying the string as some of the other suggestions here but it builds the string for you.
// Specify the provider name, server and database.
string providerName = "System.Data.SqlClient";
string serverName = ".";
string databaseName = "AdventureWorks";
// Initialize the connection string builder for the
// underlying provider.
SqlConnectionStringBuilder sqlBuilder =
new SqlConnectionStringBuilder();
// Set the properties for the data source.
sqlBuilder.DataSource = serverName;
sqlBuilder.InitialCatalog = databaseName;
sqlBuilder.IntegratedSecurity = true;
// Build the SqlConnection connection string.
string providerString = sqlBuilder.ToString();
// Initialize the EntityConnectionStringBuilder.
EntityConnectionStringBuilder entityBuilder =
new EntityConnectionStringBuilder();
//Set the provider name.
entityBuilder.Provider = providerName;
// Set the provider-specific connection string.
entityBuilder.ProviderConnectionString = providerString;
// Set the Metadata location.
entityBuilder.Metadata = #"res://*/AdventureWorksModel.csdl|
res://*/AdventureWorksModel.ssdl|
res://*/AdventureWorksModel.msl";
Console.WriteLine(entityBuilder.ToString());
using (EntityConnection conn =
new EntityConnection(entityBuilder.ToString()))
{
conn.Open();
Console.WriteLine("Just testing the connection.");
conn.Close();
}

I also faced this exact same message, but workig with a web MVC project. This message is fired when I try to auto generate the Controller from the imported model. It seems that it is not working because "that was generated from an EDMX file".
The good news is that it works if I generate the model based in the "Code First" instead of "EF Designer". The bad news is that I can't use the EF Designer if I want that the automatically controller generation works. Does not matter which from those two ways you generates your model. Once the model is generated, you use it in the same way.
Tries to remove all your emdx objects from your project and recreate the model based in the Code First instead of EF Designer. Worked for me!

Very much late but still helpful. I got stuck in a similar problem. Posted a question about on SO and was able to find a solution. You can refer to Connection String errors in C# Web Api.
My situation was I had two connection strings in web.config (you'll get to know why when go to the link). Commenting one string was raising the error you got while commenting the other one was raising error as below:
An error occurred when trying to create a controller of type 'AccountController'. Make sure that the controller has a parameterless public constructor.
what i did was: I named my first connection string as DefaultConnection and in ApplicationDbContext class constructor I gave this DefaultConnection. Now my AccountController uses this connection string and all other controllers use second connection string.
This solved my problem.

I have two projects:
One is for the generated EDMX file and all related models.
The other one is the ASP.NET MVC Web.
I encountered this issue since the connection string that I am using on the ASP.NET MVC Web project is the normal string that I use using ADO.NET connection. So what I did is the following:
Open the app.config on your EDMX project files.
Copy its connection string.
Paste it on the WEB project since this will be used when you start
the application.

How is location of |Data Directory| in connection strings resolved?

If I create an asp.net project and use entity framework to create a database, something like this is automatically added to the connection strings in the web.config:
<add name="DefaultConnection" connectionString="data source=(LocalDb)\v11.0;AttachDbFilename=|DataDirectory|\WebAppName.mdf;initial catalog=WebAppName;integrated security=True;MultipleActiveResultSets=True;App=EntityFramework" providerName="System.Data.SqlClient" />
Note that instead of a fully qualified file path, it uses |Data Directory| which, in this case, points to the 'App_Data` folder. Here's how some of the documentation explains it:
The presence of User Instance=true and AttachDBFilename=|DataDirectory| cause SqlConnectionHelper to conclude that the connection string targets SQL Server Express and triggers the database's creation. (The presence of data source=.\SQLEXPRESS in the connection string does not factor into the decision, because SqlConnectionHelper supports non-default as well as default instances of SQL Server Express.) The |DataDirectory| portion of the connection string specifies that the MDF file is located inthe App_Data directory. SqlConnectionHelper derives the database name from the MDF file name. It also creates an App_Data folder to hold the MDF if the folder doesn't already exist.
Except, if I use Entity Framework in, say, a console application, none of that is true--you'll just get an exception saying there's no file at the specified path, and it will both ignore any App_Data folder you created and fail to create one if there is none. If you remove the AttachDBFilename section altogether, it will work, but will create the database in the local output bin where the .exe file is located. Google tells me you can manually set |Data Directory| using AppDomain.SetData but apparently that's still not true for a console application (get compile error saying "An object reference is required").
So my question is, how exactly does the location of |Data Directory| get resolved? As far as I know, the fact that it differs between console apps and Asp.net apps means the resolution can't be happening solely in SQL Server Express as both are using the same installation. So is it happening in the asp.net server? Or is there a hidden settings file that gets created in asp.net projects?

Here is the code which specifies where is |DataDirectory|
GetDataDirectory
[PermissionSet(SecurityAction.Assert, Unrestricted = true)]
internal static string GetDataDirectory() {
if (HostingEnvironment.IsHosted)
return Path.Combine(HttpRuntime.AppDomainAppPath, HttpRuntime.DataDirectoryName);
string dataDir = AppDomain.CurrentDomain.GetData(s_strDataDir) as string;
if (string.IsNullOrEmpty(dataDir)) {
string appPath = null;
#if !FEATURE_PAL // FEATURE_PAL does not support ProcessModule
Process p = Process.GetCurrentProcess();
ProcessModule pm = (p != null ? p.MainModule : null);
string exeName = (pm != null ? pm.FileName : null);
if (!string.IsNullOrEmpty(exeName))
appPath = Path.GetDirectoryName(exeName);
#endif // !FEATURE_PAL
if (string.IsNullOrEmpty(appPath))
appPath = Environment.CurrentDirectory;
dataDir = Path.Combine(appPath, HttpRuntime.DataDirectoryName);
AppDomain.CurrentDomain.SetData(s_strDataDir, dataDir, new FileIOPermission(FileIOPermissionAccess.PathDiscovery, dataDir));
}
return dataDir;
}

EF Connection string without App.Config in startup project

I'm trying to abstract EF in the DAL project of my solution. I've already reached the point that EF is only known in this project.
I've created a new Console.Test application which uses my BLL, which uses my DAL. Now this new console application requires an App.Config file which contains the EF connection string. My next step would be to get rid of this App.Config file aswell, since i would like to use my BLL on several platforms.
So i've created a partial class of my derived DbContext to add an extra constructor which accepts a full connection string. In my DAL i've also created a new static method for getting the connectionstring:
public static string GetSqlConnectionString(string serverName, string databaseName)
{
SqlConnectionStringBuilder providerCs = new SqlConnectionStringBuilder();
providerCs.DataSource = serverName;
providerCs.InitialCatalog = databaseName;
providerCs.IntegratedSecurity = true;
providerCs.UserID = "*****";
providerCs.Password = "******";
var csBuilder = new EntityConnectionStringBuilder();
csBuilder.Provider = "System.Data.SqlClient";
csBuilder.ProviderConnectionString = providerCs.ToString();
csBuilder.Metadata = "res://Prodomus.DAL/DataObjects.Entities.Model.csdl|res://Prodomus.DAL/DataObjects.Entities.Model.ssdl|res://Prodomus.DAL/DataObjects.Entities.Model.msl";
return csBuilder.ToString();
}
Now my problem is that i keep getting this error message stating: 'The underlying provider failed to open.'. I know for sure that the credentials i've used are correct, this also goes for the servername aswell as the databasename. Am i missing something here? Any help will be very much appreciated.
Thnx in advance!

You cannot mix Integrated security and username/password

Add a connection string to local user config file throws lock exception

I have developed a WinForm C# app that use ADO.NET Entity Framework for storing data.
I would like each user to have a database stored in their appdata\local folder but when I try to add the connection string to the users local app.config file I constantly get the error "ConfigurationSection properties cannot be edited when locked."
After I did some research I discovered the allowExeDefinition section setting.
I tried adding this setting for the connectionString section in the app.config file and at runtime (see code below) but I still get the same error whenever I try to save the configuration.
This is the code I use:
var connectionString = string.Format(ConnectionStringBase, dbLocation);
var exeConf = ConfigurationManager
.OpenExeConfiguration(ConfigurationUserLevel.PerUserRoamingAndLocal);
var connectionStringSettings =
new ConnectionStringSettings(
"DatabaseEntities",
connectionString,
ProviderName);
exeConf.ConnectionStrings
.SectionInformation
.AllowExeDefinition = ConfigurationAllowExeDefinition.MachineToLocalUser;
exeConf.ConnectionStrings.ConnectionStrings.Add(connectionStringSettings);
exeConf.Save(ConfigurationSaveMode.Minimal);
I have tried to search for a solution for this issue for days but I haven't been able to find anything usefull besides that I am considering storing the connection string in the users settings instead as a workaround but it feels kinda hackish.

Alright, instead of updating the app.config file I decided to create the connectionstring on runtime and pass it to the entity set constructor.
So when I initialize the entity set I use the following code instead:
var connectionString = string.Format(ConnectionStringBase, dbLocation);
var entities = new DatabaseEntities(connectionString);
The only thing to note is that if the connection string contains " you should replace these with single quotes ( ' ).