Get connection string from App.config

问题:

var connection = ConnectionFactory.GetConnection(
    ConfigurationManager.ConnectionStrings[\"Test\"]
    .ConnectionString, DataBaseProvider);

And this is my App.config:

<?xml version=\"1.0\" encoding=\"utf-8\" ?>
<configuration>
    <connectionStrings>
        <add name=\"Test\" connectionString=\"Data Source=.;Initial Catalog=OmidPayamak;Integrated Security=True\" providerName=\"System.Data.SqlClient\" />
    </connectionStrings>
</configuration>

But when my project runs this is my error:

Object reference not set to an instance of an object.

回答1:

Can\'t you just do the following:

var connection = 
    System.Configuration.ConfigurationManager.
    ConnectionStrings[\"Test\"].ConnectionString;

Your assembly also needs a reference to System.Configuration.dll

回答2:

Since this is very common question I have prepared some screen shots from Visual Studio to make it easy to follow in 4 simple steps.

回答3:

string str = Properties.Settings.Default.myConnectionString; 

回答4:

Also check that you\'ve included the System.Configuration dll under your references. Without it, you won\'t have access to the ConfigurationManager class in the System.Configuration namespace.

回答5:

First Add a reference of System.Configuration to your page.

using System.Configuration;

Then According to your app.config get the connection string as follow.

string conStr = ConfigurationManager.ConnectionStrings[\"Test\"].ToString();

That\'s it now you have your connection string in your hand and you can use it.

回答6:

//Get Connection from web.config file
public static OdbcConnection getConnection()
{
    OdbcConnection con = new OdbcConnection();
    con.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings[\"con\"].ConnectionString;
    return con;     
}

回答7:

Try this out

string abc = ConfigurationManager.ConnectionStrings[\"CharityManagement\"].ConnectionString;

回答8:

1) Create a new form and add this:

Imports System.Configuration
Imports Operaciones.My.MySettings

Public NotInheritable Class frmconexion

    Private Shared _cnx As String
    Public Shared Property ConexionMySQL() As String
        Get
            Return My.MySettings.Default.conexionbd
        End Get
        Private Set(ByVal value As String)
            _cnx = value
        End Set
    End Property

End Class

then when you want to use the connection do this in ur form:

 Private Sub frmInsert_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

Dim cn As New MySqlConnection(frmconexion.ConexionMySQL)
cn.open()

and thats it. You will be connected to the DB and can do stuff.

This is for vb.net but the logic is the same.

回答9:

Have you tried:

var connection = new ConnectionFactory().GetConnection(
    ConfigurationManager.ConnectionStrings[\"Test\"]
    .ConnectionString, DataBaseProvider);

回答10:

I had the same Issue. my solution was built up from two projects. A Class library and a website referencing to the class library project. the problem was that i was trying to access the App.config in my Class library project but the system was searching in Web.config of the website. I put the connection string inside Web.config and ... problem solved!

The main reason was that despite ConfigurationManager was used in another assembly it was searching inside the runnig project .

回答11:

string sTemp = System.Configuration.ConfigurationManager.ConnectionStrings[\"myDB In app.config\"].ConnectionString;

回答12:

You can fetch the connection string by using below line of code -

using System; using System.Configuration;

var connectionString=ConfigurationManager.ConnectionStrings[\"MyConnectionString\"].ConnectionString;

Here is a reference : Connection String from App.config

回答13:

It seems like problem is not with reference, you are getting connectionstring as null so please make sure you have added the value to the config file your running project meaning the main program/library that gets started/executed first.

回答14:

It is possible that the OP in this question is trying to use an App.Config within a dll.

In this case, the code is actually trying to access the App.Config of the executable and not the dll. Since the name is not found, you get a Null returned, hence the exception shown.

The following post may be helpful: ConnectionString from app.config of a DLL is null

回答15:

First you have to add System.Configuration reference to your project and then use below code to get connection string.

_connectionString = ConfigurationManager.ConnectionStrings[\"MYSQLConnection\"].ConnectionString.ToString();

回答16:

This worked for me:

string connection = System.Configuration.ConfigurationManager.ConnectionStrings[\"Test\"].ConnectionString;

Outputs:

Data Source=.;Initial Catalog=OmidPayamak;IntegratedSecurity=True\"

回答17:

I referenced System.Configuration library and I have the same error. The debug files had not their app.config, create manually this file. The error is, I solved this copying the file \"appname.exe.config\" in debug folder. The IDE was not create the file.

回答18:

I solved the problem by using the index to read the string and checking one by one. Reading using the name still gives the same error.
I have the problem when I develop a C# window application, I did not have the problem in my asp.net application. There must be something in the setting which is not right.