Object reference not set to an instance of an object. - ConfigurationManager.ConnectionString

Question

I am trying to connect to my local database to select a sql database and print the column names but I keep getting this exception:

System.NullReferenceException: 'Object reference not set to an instance of an object.'

System.Configuration.ConnectionStringSettingsCollection.this[string].get returned null.

Can somebody help me?

    string constr = 
  ConfigurationManager.ConnectionStrings[@"Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Program Files\Microsoft SQL Server\MSSQL11.SQLEXPRESS\MSSQL\DATA\NORTHWND.MDF;Integrated Security=True;"].ConnectionString;

    SqlConnection con = new SqlConnection(constr);

You already have your connection string in the form of `constr`. The configuration manager's connection string is meant for retrieving a ConnectionString setting from a config file by name. You're currently using the entirety of a connection string as the name for lookup. — Jonathon Chase, Jan 08 '19 at 22:08
The variable `constr` is your connection string. You are using it as an index into the dictionary of connection strings that the `ConfigurationManager` maintains: `ConfigurationManager.ConnectionStrings[constr]`. Either use the connection string alone, or use the name of the string that you have in the config file — Flydog57, Jan 08 '19 at 22:08
Ok I tried fixing it a little and it still has the same result — Anthony Karounis, Jan 08 '19 at 22:51

Viggo Lundén · Answer 1 · 2019-01-08T22:13:44.343

0

You're initializing the SqlConnection a little goofy. Try this:

SqlConnection con = new SqlConnection(constr);

edited Jan 08 '19 at 22:13

answered Jan 08 '19 at 22:08

Viggo Lundén

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I have to use ConfigurationManager.ConnectionString because it's needed later on in the code. So you can understand better I'm trying to replicate the code from the GetData() method here: https://www.aspsnippets.com/Articles/Display-data-from-database-in-HTML-table-in-ASPNet.aspx – Anthony Karounis Jan 08 '19 at 22:32
It's hard to see what the problem is without seeing the rest of the code but try using: `ConfigurationManager.ConnectionStrings["constr"]` instead of `ConfigurationManager.ConnectionStrings[constr]` – Viggo Lundén Jan 08 '19 at 22:40
Ok I edited the code a little and it still has the same result – Anthony Karounis Jan 08 '19 at 22:54

score 0 · Accepted Answer · answered Jan 08 '19 at 22:56

If you need to use ConfigurationManager.ConnectionStrings then your connection string needs to be in your web.config in the configuration/connectionStrings section similar to this:

<configuration>
   <connectionStrings>
            <add name="db" connectionString="Data 
          Source=.\SQLEXPRESS;AttachDbFilename=C:\Program Files\Microsoft SQL 
          Server\MSSQL11.SQLEXPRESS\MSSQL\DATA\NORTHWND.MDF;Integrated Security=True;"/>
   </connectionStrings>
<configuration/>

You then access it by the value of the name attribute, like this:

var conn = new SqlConnection(ConfigurationManager.ConnectionStrings["db"].ConnectionString);

Yup I think that did the trick. Thanks! – Anthony Karounis Jan 08 '19 at 23:52 — Anthony Karounis, Jan 08 '19 at 23:52

Object reference not set to an instance of an object. - ConfigurationManager.ConnectionString

2 Answers2