Why am I getting this error: The ConnectionString property has not been initialized

I have searched and tried everything but can’t figure this one out. I am trying to do something simple but it seems as though I am doing something wrong. Basically, any user that has made a deposit, I want to return true, if they have not, I want to return false. This should be easy I suppose but I am stumped on this.

Here is the error:

The ConnectionString property has not been initialized.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.InvalidOperationException: The ConnectionString property has not been initialized.

Source Error:

Line 59:         Cmd.Parameters.AddWithValue("@UserID", userId);
Line 60:         con.Open();
Line 61: 
Line 62:         result = (int)Cmd.ExecuteScalar();

Here is the top of the stack trace:
[InvalidOperationException: The ConnectionString property has not been initialized.]
System.Data.SqlClient.SqlConnection.PermissionDemand() +4879939
System.Data.SqlClient.SqlConnectionFactory.PermissionDemand(DbConnection outerConnection) +20
System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory) +117
System.Data.SqlClient.SqlConnection.Open() +122
Here is my method for returning true or false:

public static bool HasDeposit(int userId)
{
    int result = 0;
    //since executeScalar is intended to retreive only a single value
    //from a query, we select the number of results instead of the email address
    //of each matching result.
    string queryTransaction = "SELECT COUNT(UserID) FROM Transaction WHERE TransactionTypeID = 6 AND UserID = @UserID";
    string constr = System.Configuration.ConfigurationManager.AppSettings["ConnectionString"];
    SqlConnection con = new SqlConnection(constr);

    SqlCommand Cmd = new SqlCommand(queryTransaction, con);

    Cmd.Parameters.AddWithValue("@UserID", userId);
    con.Open();

    result = (int)Cmd.ExecuteScalar();

    //returning a boolean comparator works like this :
    //will return true if the result is greater than zero, but false if it is not.
    con.Close();
    return result > 0;
}

Any help / guidance on this would be much appreciated.

Answers:

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Method 1

If you have your connection strings in your configuration like this

<connectionStrings>
    <add name="ConnectionString" connectionString="data source=.;Initial Catalog=MyDatabase;Integrated Security=SSPI" providerName="System.Data.SqlClient" />
</connectionStrings>

Then you will need to use this method to access it System.Configuration.ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString

You should also wrap your data access in using statements so that you don’t leak connections and flood the pool. Here’s an updated example with using statements.

public static bool HasDeposit(int userId)
{
    //since executeScalar is intended to retreive only a single value
    //from a query, we select the number of results instead of the email address
    //of each matching result.
    const string queryTransaction = "SELECT COUNT(UserID) FROM Transaction WHERE TransactionTypeID = 6 AND UserID = @UserID";

    var constr = System.Configuration.ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;

    using (var con = new SqlConnection(constr))
    {
        using (var cmd = new SqlCommand(queryTransaction, con))
        {
            cmd.Parameters.AddWithValue("@UserID", userId);
            con.Open();

            var result = (int)cmd.ExecuteScalar();

            //returning a boolean comparator works like this :
            //will return true if the result is greater than zero, but false if it is not.
            return result > 0;
        }
    }
}

Method 2

In web.config :

<appSettings>
    <add key="ConnectionString" value="Data Source=.SQLEXPRESS;AttachDbFilename=|DataDirectory|Database.mdf;Integrated Security=True;User Instance=True"/>
</appSettings>

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0